That sounds like a plot device for a murder mystery show. Stupid detective: "Why didn't he escape the fire, the smoke detectors were working?" Smart CSI: "Yes but the killer removed the battery and blew smoke into the detector setting the new baseline tolerance higher than a fire." Killer: "And I would have gotten away with it too if it weren't for you meddling kids" ROLL CREDITS
I expect that unless you did that immediately before setting the fire, or maybe took the battery out, set the fire, blew a mouthful of smoke in and reconnected the battery immediately before scooting, they would eventually reset and recalibrate down to a lower set point. The way you would sensibly program something like that is to take the differential of the detected reflection level, as well as considering the DC level itself. Signal value rising faster than a certain cutoff rate, or the level simply being higher than a particular set point anyway (indicating an environment already so smoky or dusty that your detector hasn't a chance of working as intended) = set off the alarm. That then protects both against fires that are close by (causing the internal smoke density to rise quite fast), with the alarm going off even before the smoke actually reaches a dangerous level, and the more insidious case of a slower or more distant burn filling the air with smoke too slowly to set the detector off by rise rate alone, but reaching a dangerous enough level that if you haven't already picked it up by smelling it building up, or being awoken with a coughing fit, at a point where you could still safely escape, then you definitely need an audible jolt to get you out before you suffocate. With the additional case that if you connect the battery and the environment is already dangerously smoky, it will go off immediately... with the user then having the option of just taking the battery back out (as the alarm will trigger before you've even properly clicked the terminals into the connector, let alone put the lid back on), or taking heed of the warning and vacating the area.
And, well, if you had the opportunity to do such a thing, you could probably have just took the battery out, set the fire, then snuck back in afterwards to reconnect the battery. Or cut one of the cables right where it's soldered to the board (or desoldered it?), set the fire almost immediately underneath, and let the flames destroy - or at least heavily distort and disguise - the evidence for you...
@@markpenrice6253 Or just stick something to the ceiling with wax, enclosing the detector. Set fire, it's well established by the time the wax melts and drops the cover, and shortly any remnant wax will be vaporizing and the cover will be a nondescript patch of melted plastic on the floor, possibly intermingled with the remnant plastics from the detector body itself.
@@dutchdrifter8740 no, they don’t. Manufacturers make the name brand ones for about 5 bucks each, they then charge people 20-30 bucks for that same item. (statement is true for everything actually). Life saving equipment should be forced to be sold at reasonable markups. But this is a greedy capitalist society, so that’s not gonna happen.
That's actually a poor design. What happens is there's a weak battery, the device detects smoke and starts alarming for a while, then the voltage drops underneath the operating threshold and it resets. Then it will remain silent rather than trying to alarm again.
@@volo870 Most people are too lazy to. That's why California banned smoke detectors with removable batteries; they have to be 10 year permanent lithium type. Poor people were apparently not replacing and worse taking the batteries out.
@@straightpipediesel Why the hell would you buy a smoke detector then? It's better to rely on your smell and guts than on a malfunctioning device. In my neck of the woods smoke detectors are VERY rare. But those installed are being taken care of.
The volunteer fire department I am on has always installed smoke detectors for free for the elderly and folks who can’t afford it. Otherwise we sell them for $5 US, which is our cost from Kidde Company. In America the first week in October is Fire Prevention Week and it’s suggested to change the battery out every 6 months which normally is around daylight savings time where we change the time of day either by falling back 1 hour or moving ahead by 1 hour. The new dual smoke detectors we got earlier this year is touted as both photoelectric and ionization. I should send you one to dismantle and test.
The fire department here says test once a year and change the battery 6 months later. Also, you are supposed to replace your smoke detector every 10 years minimum. Kidde (pronounced kid-uh for those that care) now sells 9V batteries that they guarantee for 10 years in their smoke detectors. One detector, one battery, one decade. I also use a carbon monoxide alarm in my room and between my furnace and water heater.
I really appreciate all the great information and explanations, I have always enjoyed taking stuff apart to see how it works, the circuit boards and what not are so confusing but i'm slowly understand how all the little do-dads work, great video! :)
+Experimental Fun "I have always enjoyed taking stuff apart to see how it works" For many years I did the same, and invariably ended up breaking stuff; but in due course I learned how to fix stuff and then how to make stuff.
Yup. I've taken apart tons of stuff I got for free from the local thrift store. If you find somewhere local that is already tossing stuff that doesn't power on, it's a great source for random parts and repair/troubleshooting/circuit lessons. Some second hand stores are even paying for hazmat recycling just to throw out electronics stuff. So your actually saving them money by taking the e-junk off their hands. Eventually it dawned on me that my time is better spent learning with intentionally selected components where I know what I have, know that it works, and have spares readily available -if- or rather when I make a mistake. It's still handy to have a bunch of junk boards laying around to reference to though. Personally, I limit playing with junk box components mostly by the datasheet. If the DS is a page or few, it's worth goofing around with. If the DS is longer, that's the kind of thing I want new spares for. There's nothing quite as annoying as spending a bunch of time troubleshooting a broken part or breaking something after spending time on it without a spare on hand. I also highly recommend trying to remove and reattach some more advanced surface mounted packages like QFN's on junk boards. It's very easy to assume "I'll fix this easily" just to learn the reason why rework stations are a thing. I think the best stuff to salvage and study are power supplies. There are lots of cool things you can learn, and no matter your field of interest your going to need at least one power supply. -Jake
Back in the mid 70s I had a school holiday job working for a company that among other things made a photoelectric smoke detector. It was based on a tiny incandescent lamp, 2 CDS cells and an old 741 op-amp in a round metal can. This was before microcontrollers or dedicated chips. From memory it compared the detected light from 2 sensors via different paths in a black chamber. Motorola made a dedicated chip back in the early-mid 80s MC14466 - a later version may still be available. I now work with a smoke detector that used a dedicated chip until a year or two back when the manufacturer changed to a 14-pin PIC micro. An op-amp circuit connects the IR sensor to the PIC. A lot more parts than the detector shown here, but still relatively low cost from the source.
"cap tolerances are always negative" - false. It depends on the manufacturer, and even then, expect 10% to be outliers. Source: I measured about 200 caps just to see for myself.
I believe the 4.7R is an emitter swamping resistor to keep the transistor gain constant over a wide temperature range, the B-E junction forward drop is quite temperature sensitive and would cause the LED brightness to vary with temperature. I would expect that would complicate the sensing threshold (and battery drain). A Mosfet would be a better choice, but needs more voltage. I just bought a number of smoke detectors and did a little research to find, surprisingly, the Photoelectric type are actually superior in aggressive fires, where the Ionization type often take several minutes to respond in these conditions. They are also less likely to false with cooking vapors and such than the ionization models. The Ionization detectors are the response time winners for smoldering fires however. It seems a combination of the two might be ideal. Thanks for all the great videos
If you have the money buy a more costly one but as a student i.e. a cheap one is better than none at all. You saw the circuit they came a long way and chinese slave markets made it possible to have quiete good ones for 10 bucks or less
Cool video! I take apart old/faulty ionization type detectors for the Americium-241 sealed sources. I have a lot of sources, because radioactivity is my favorite hobby. Am-241 is a great alpha particle and low energy gamma source. Many modern ionization type detectors also have a photoelectric chamber too. Older industrial ionization type detectors used a higher activity of Am-241, usually with two separate Am-241 sources. One stronger source would detect smoke from early fires, and a second weaker source in an enclosed chamber for intense smoldering fires. Anything that passes between the Am-241 source, such as a gas leak, or even very high humidity has the potential to attenuate the alpha particles, causing a drop in the current and triggering the alarm circuit.
Fife Council considers smoke detectors an investment - better value than sending out the fire-brigade - and will install them in your house free, so "cheap" isn't needed here.
Many of the fire departments have teams that will fit them free too. But the downside of that is that if they reduce the number of fires they get their funding cut. Because that's the mentality of politicians.
It is still the same number of fires with a lower amount of fatal casualties. Stopping funding would be mad. Certain British politicians do not seem to be interested in serving the public interest or common good.
Come to rural America where you have to pay a yearly fee or the Fire department will just let your house burn down. www.npr.org/sections/thetwo-way/2010/10/08/130436382/they-didn-t-pay-the-fee-firefighters-watch-tennessee-family-s-house-burn
Even if you don't need them as actual life saving measures, you could use them for... Let's say hacking in some smoke-triggered automation. Wouldn't mind adding this and a latch relay to a 3D printer or something.
It works very similar to how a surface scatter turbidimeter works. They create a smooth pool of flowing water, a light shines on the surface and is reflected off into a cone of non-reflective paint. Only particulates in the water reflect light into the sensor. The beam shines at the water at about a 60 degree angle, so the light reflecting off the water goes equal and opposite. The sensor is 45 degrees off the water however, so it only sees particulate reflections, not water reflections.
Surface scatter turbidity monitors are routinely found in clean water treatment plants where they are used to monitor drinking water quality, which in Britain is tightly regulated. Turbidity can be loosely described as cloudiness, which at high levels is unsightly, and can indicate contamination.
You're actually the best youtuber to learn the basics of these things thank you!! Sad that i didn't find someone like you in the past 8 years of experience in electronics...
I used to work in that industry. The MSP430 family was actually a common ish choice for optical smoke detectors due to its great low power modes and rich ADC options. However at least the engineers I knew of eventually moved back to an ASIC solution - so the cost benefit is right on the edge. BTW in some instances the device may not go to lobat mode unless it sees VBat sag when load is turned on - in this case, the emitter LED.
Good video! It was a big relief when my local council installed mains operated smoke and heat detectors. You do sleep better, what with so many lithium based products laying around, many on charge while we sleep too!
The year 1921: Cinema fire caused by motion picture film. The year 2021: House fire caused by lithium ion battery in thermal runaway... One step forward, one step back... The thing in common is both have their own oxidizer.
I have 2 FireAngel ST-622 alarms supplied by my fire brigade. These are supposed to have a 10 year battery life. Both now are giving a low battery alarm after only a year or so. The batteries are not replaceable. Took one apart and the battery was still good. Contacted the manufacturer and was told to contact the seller.
11:01 the lines in a transformer symbol are supposed to indicate the magnetic core material (iron or ferrite). The odd power rail routing may be an abandoned plan to detect board damage or just incompetence.
John Francis Doe It really does not matter in this case as it is just a rough and dirty drawing to convey the basic logic behind the circuit, which is all that is really of importance in these discussions. What surprises me far more in this example is that they got away with the far off filter capacitor as most low dropout regulators tend to be very particular about placement location and the ESR of their filter capacities lest they go into oscillation.
Clive, the big scare is that so little is said about the fact that even the best ionization detectors (which are fastet to respond) go dead in 7-10 years, and just changing the battery won't fix that. New detectors with a built-in 10 year battery fix that, toss and replace the whole thing. It costs less than 10 battery changes and won't wake you up 10x in the middle of the night. Canned smoke, for a real test, is worthwhile for all of them. Photodetector alarm for 4 bucks? Priceless!
If you want the alarm to be sent out over bt or wifi, it only needs power once when you configure it, and once more when there's a fire. But the radio chips add $5 even to cell phones, which means $10-20 more in the retail price. Ante up.
I've got the BRK ones with an RF base wired into the house lighting circuits they all have 10 year lives, and Li batteries for backup. They are the ionisation and optical ones. Since I had to fit mains interlinked alarms when I built a new house extension to meet building regs it was easiest to do it this way and I can fit extra ones or replacements in a matter of seconds. Recently bought 2 spare bases from a closing Homebase for £7 each. Newer UK houses will all have mains detectors so these battery driven ones will be of little or no use in them.
I recommend changing smoke detectors completely every five years. They do accumulate dust. In greasy or dusty areas they should be changed sooner or a rate of rise detector fitted.
I'll admit, there's an elegance to the design that appeals, in much the same way there's elegance (if you know where to look) in a Trabant. Elegant or not, I'll still not entrust either with my children's wellbeing! Cheers Clive!
Buying smoke detectors in bulk, we spend about $300 for about 15 of them, minus batteries. They're good for 10 years (again, minus batteries), so for about $50 a year for all of them (including batteries every year) ... it's well worth the price for the safety!!! Ours are also hardwired with battery backup, so they normally run off the mains. And they have an alarm wire, so when one goes off, the rest of them also start beeping. Makes quite a racket, LOL.
The zener diode that is missing is meant for the micro controller to get more of an accurate voltage reference of the battery state and sound a low battery alarm even when ran on stable the mains power, this smoke alarm can't because it has a voltage regulator blocking the actual voltage reference of the battery.
Normally test benches are used for simulating logic controllers, so you dont have to programm the chip itself, but you test your code in the testbench and if you tested it throughly you can start with your prototype in the hardware. Same way it is done with using field programmable logic arrays for describing the hardware, simulating and testing it in a testbench and then you can put that into a one time programmable chip
There is a RUclipsr named David McLuckie who did a teardown video covering an even cheaper smoke alarm he found online (On AliExpress). That one was tested with a simulated fire and appeared to fail to operate. What he found inside was a much smaller circuit board than the one looked at here which looked as if the only thing on it was the detector itself until David pointed out a tiny buzzer. The scary thing is, apart from a lack of battery cover, it looked just like the one torn down in this video and the detector Clive tore down in 2015.
Irrespective of your negative comments the engineering design is very interesting and represents a totally different take on design and minimising costs. Just think, no dangerous radioactive isotopes around. I design PCBs using Cadence /Orcad and when I think I have optimised the design we send it to a Chinese design house that reviews our work. It is amazing the cost savings they come up with. We save a fortune every year implementing their suggestions. Chinese designers have different criteria to other cultures - which is why so many leading Western countries do initial designs and, ultimately, production there.
The optical detectors are widely available, but often use a dedicated chip that can test the chamber for functionality by detecting low reflections of test pulses. It also differentiates between temporary dust reflections and smoke, and also has proper low battery warnings. The cheap units (only marginally cheaper that the real thing) have debatable detecting ability, can drain the batteries fast and not warn about low voltage. Some have sounders that are as loud as your microwave oven beeper. They're basically fake smoke detectors.
Clive, I think the purpose of the 10uF and 1K resistor is to have a low current charge and high current discharge. The life of an alkaline battery can be 2x to 4x longer at lower current discharge rates.
Surprisingly the standards do not allow a mute function. If it's done properly the sampling can be done less than 10s. Smoke should be detected before it is visible. This circuit does not have enough gain to allow to much contamination build up. Cheap chambers can melt with heat before the smoke is detected.
For some reason this video reminds me of the time I was stapling up a cloth on a wall. On the other side of the wall was a smoke detector. The vibration from the stapling must have done something but the smoke detector caught fire, but luckily alarmed itself before it died. It's very ironic when smoke detectors catch fire.
I have a dual-mode detector and I change the whole unit every year. I love my life and its worth the $25-$30 a year for me. I pretend I spent that money having a few beers in a pub, and I don't even drink!
I would add another every year if I was that paranoid just because it would be fun to cover the entire fucking celling with those red eyed blinking boys.
You can see the flashes from the LED again at 16:38 for a few seconds... and a couple more times later on... so the camera may be shifting around a bit with the focus, etc. Interesting little unit... and nice to see those 3c micros in the wild! Hopefully more people start talking about them and see them become a thing of interest for DIYers... no excuse not to use a micro for 3c! ;)
This makes me think that the free smoke alarm the fire brigade put on the landing a couple years back is an optical one, cos it triggered when I was messing about with my smoke machine, the old alarm didn't do such things cos it was a nuclear reactor type, or whatever it is with the little Americium bit in it... :)
twocvbloke The other type is an ionizing detector. The best smoke detectors contain both optical and ionizing units as each has its strength and weaknesses, what one detects earlier the other takes longer and vice-versa. But most of the less expensive detectors are optical and they are very good at detecting fires that produce a lot of smoke while the ionizing detectors are better at detecting slow smoldering fires and the combustible gasses they give off well before they have produced much detectable smoke - so one is great at detecting slow simmering fires and the other fires that are fast burning and/or produce a lot of smoke (or steam, even).
Ethan Poole the landlord put a small rubbish battery powered one on the ceiling in the kitchen a few years ago, what is that one? Its over my gas cooker, it's fine if I use the oven but when I boil things in water on the hob the bloody thing goes off, it's done so twice this week once with rice and once with a boiled egg, I had to take the battery out with the egg as flapping a towel at it didn't shut it up. Is that the steam or the burned gas
I was working in a hospital once. The builders had covered up all the smoke detectors to prevent dust ingress. On the day of recommisioning, the had reenabled the zone detection. As they were removing the covers, the elasticated cover flicked dust up into the detector and set of the alarm!
NB I have no clue of what I'm talking about but I was thinking that maybe the idea behind the detour to connect that capacitor was to keep an option open for connecting multiple smoke alarms in a network. Where the electrolytic capacitors would be an endpoint for the transmission line.
If you have enough memory , after your first program you can overwrite everything to 0 , usually means NOP and program new application from there on. Not having to just bin it straight away.
At 10:40 that should be a thyristor and not a bipolar transistor. As this should be a latching circuit, although there is no reset switch for some reason.
I wonder if fast pulsing is because it;s looking for a rise in light from pulse to pulse rather than absolute level. Probably not good for battery life though
A previous unit based on a dedicated chip pulsed slower, but woke and increased the sample rate if it detected something suspicious. Maybe this one was in a heightened alert mode. I might wire in an extra LED with suitable resistor to allow monitoring of sample rate in a more realistic way.
I would suggest it's looking for a high degree of match to that pulse in order to weed out false positives, changing up the rate would only help that aspect.
Nobody buys a 4$ smoke detector for their own home. Landlords buy them. I'll bet that besides Big Clive, most people who buy these buy them in packs of fifty.
In my experience landlords just don't replace them even 50 years later as long as they work. I did not trust the ones in my last apartment so old they made a buzz not beep which took us an hour to realize one was going off below us...and did not even have battery backup. Lease says they can not be removed or modified so I installed my own new name brand alarm adjacent to theirs.
Code will probably require hardwired interconnected systems for rental units. These are for people who want the security of a smoke alarm, but only want to put a fiver toward their fire safety budget. Oh, and the cost of a warranty is not included here. Even more expensive "cheap" smoke alarms have high failure rates. They come with a warranty though, which you are paying for in the price. Part of the $13/£10 you are paying is going toward sending you a new one when it breaks in 6 months.
Yep slum landlords. Dishonest landlords. Cheapskate landlords. Or people that just want to collect the insurance when the smoke detectors don't work. Need I say more don't think so.
Thankfully in Australia (or at least the state I am in) has laws requiring landlords to have proper smoke alarms (and my landlord recently send a guy out to check the smoke alarm for compliance)
Andy Lundell, if they do they probably take the batteries out the first time they false alarm, like when they've burned their toast. I have a full fledged commercial Fire alarm system, but that's only because I designed it when I worked for a company that made them.
My best was when I emptied a lunatic asylum accidentally. I was working on the alarm system and it went off. The system used a huge air-raid type siren on the roof and my legs literally went like jelly when it went off.
Air raid siren in a lunatic asylum? That's sounds like Broadmoor! They are talking about decommissioning their former WWII air raid sirens - it would be amazing if they could send one to you for a tear down.
@@bigclivedotcom Reminds me of the time when I was working overtime, during the weekend, alone in a data center. Which was not known to the guys who thought it would be empty during the weekend, for their test of the fire suppression system. I was not aware of them and they were not aware of me. The fire suppression system just flushes the room with CO2. The ingenious part is the acoustic alarm. The high pressure CO2 enters the room through a klaxon. Extremely simple, extremely effective and extremely right behind me. It was so shocking that I was paralyzed and couldn't muster any clear thought for a few seconds.
It could. It would depend on finding xrays with high enough energy to penetrate the plastic but not so much that it causes damage to other devices within the chip.
My landlord had a few smoke detectors mounted in my flat, since they are now required by law. I took one off to have a closer look, and it was also one of these optical jobbys. What surprised me was that it actually had a replaceable battery (of some weird uncommon format), while these devices were clearly rated for 10 years of battery life and then to be disposed of - not the battery changed. So I wonder if there are some things in such a smoke detector that age and make it so that it doesn't detect the smoke any more after such a long time, since if the battery is replaceable, you could just replace that and keep the unit?
You do get dust and dirt building up in them over time. Especially when near a steamy or oily area like a kitchen. It's a good idea to replace them fairly regularly.
Related to 13:00, while the circuit is not relying on the 4.7 ohm resistor being in the emitter for limiting the current, it seems to me it would not do much at all anyway in that role - assuming a 3V control signal from the CPU, by the time the emitter would raise to 2.4V, the LED would be passing a full 0.5 amps if the 1K wouldn't prevent all of that in the first place. Is 0.5A a typical absolute maximum pulse current rating for IR LEDs...? :)
Is the zener just extra protection for the microcontroller 3.3V supply (prevents overvoltage in the event of regulator issues or external EM interference) ?
The older style smoke alarms had some sort of dedicated 14 pin chip which monitors in pulses, the change in resistance between two terminals (plates) with a trace of uranium of some sort placed in between the plates that reacted to smoke.
Do you know why smoke detectors use relatively low capacity 9v batteries instead of higher capacity AA or AAA? Is there something about the sensor or buzzer that requires higher voltage?
There use to be 2 types. The ionisation kind which is interesting since it contains Americium 241, about 0.3 ug (I think), which comes out to 0.9 uCi. It is an artificial element. It is somewhat fissile, which means that you can make a nuclear bomb with it, if you can collect about 10 to 20 kg. The other type is the photodetector type. A new one on the market is heat detection.
Couldnt they have built it inverted? So the receiver always gets hit by the transmitters light, and the receiver measures the lights intensity. When there is smoke, less light is received and sound the alarm.
Does it have any low voltage warning mechanism or not? I also bought one of these. It didn't appear to have any low voltage warning, so I stopped using it.
i hired the "eh ehm... excuse me!!" lady you find everywhere while you light up a cig, no maintainance and honestly you need a really clever algorithm to tell if it's really smoke or whatever else, that transistor amplifier looks really lame, or maybe it beeps just when the heroes jump off, with an explosion on the back
Does the test button just send a signal to the microcontroller that turns on the peizo, or does it turn the LED in the chamber up to full brightness to check that it is detecting? (In the same way the test button on an RCD mimicks the fault condition, rather than just switching off)
Can't verify it, but the 10Meg resistor with the transistor (and the suspected photo diode)? My guess is that the transistor is actually a FET and the 10Meg guy is its pull-down. That would create a nice logic level (vs. an analog signal) at the output though.
Hmmm...the photo detector side has transistor-beta-dependent gain. So exact photo current required to make the “CPU” signal go LOW is dependent upon the transistor beta. That makes “zeroing” the residual light somewhat tricky. What am I missing? Perhaps “CPU” signal goes into an A/D converter and further analysis is performed by the microcontroller.
I've got A xiaomi smart smoke alarm. It's brilliant. Keep me upto date on if it's working or not, and let's me sail down the sensitivity when the kids are cooking, and it will ramp itself back up in a give time. Plusr it has a hub, that other smarts hang off, which I keep in the bedroom, at also sets of ab alarm, and flashes red. Probably a bit pricey if just being bought for a smoke alarm, but cis I wad already using the xiaomi mija hub, it took a punt, and been happy with it.
They cost less in a LOCAL store and it will be at least somewhat safe. Not that it matters because as soon as they start to warn the battery is empty they get pulled out and not replaced
At least this has a microcontroller. I have one on my possession, not autonomous but connects to a fire alarm panel, that the only IC it has is an HEF4013BT that appears to be a dual D-type flip-flop. It's diagram is much more complicated, with a lot more transistors but I don't think it has the required functionality. A lot of false alarms by these fire detectors and they are not made in China but in Spain.
It sounds like it may be based on simple voltage threshold or transition circuitry. A processor allows better filtering against nuisance alarms from slight transients of dust or smoke.
Here's wierd question,, it's seems like it would take a while to detect smoke, with optical sensors, because the smoke has to creep into the plastic housing then creep into the sensor housing. Like I would think you need a fan to suck smoke Into it?
@bigclivedotcom ohh ok, I was thinking like a stream of smoke at first, but in a closed room, I get it now. I'm only a amateur level tinkerer, so I find your videos are the best at explaining how all these electronics work. Thank you all the way from 🇨🇦.
If that is the chip that Dave showed the website for, or one of their models at least. It has a full blown development environment complete with documentation down to timing diagrams and translated engineer notes. When I seen that I was surprised by the level of support by the vendor right out the gate. Some of the info when he was flipping through on his video you don't need to use the chip but would want to know to really squeeze out a lot of work.
9:02 Maybe they needed some kind of inductance there? It doesn't make a lot of sense (why would you add an inductor?) but having such a roundabout wire might add some inductance.
I have the same but i change adjust potentiometer to multi turn for better sensitivity adjust and add switch in front to turn off and instant discharge electricity for alarm.
no mute button? so if you're coming out of the shower and that thing starts beeping you have to take it down and take the battery out. then you'd never hang that back
Most fire brigades in the UK will fit smoke detectors for free. They are the FireAngel devices which would otherwise cost around £10. They have a 10 year guaranteed life Li-ion battery which does not last 10 years. When the battery runs out and it starts chirping you phone FireAngel and they send you a new one.
+Do R/C! A lot of times people miss smoke detector failures because they don't test them often enough. Assuming that smart detectors can run a thorough self-test and report faults to the user right away, it's one of those few cases where having domestic tech connected to the network is a *good* thing! :-)
Everybody's on the 3c controller this week! ruclips.net/video/VYhAGnsnO7w/видео.html The manufacturer's website appears to have Multi-Time-Programmable controllers too, they're marked as MTP on the "Catalog" links. Can't find a supplier though.
I'm kind of curious as to what vaping device you're using to test the detector with? Seems to be something a bit more substantial than the EGO style devices you usually use.
Too late, my uncle's house already burned down just a few weeks ago. The investigation is not yet complete, but they are honing in on the photovoltaic solar system! I did get a picture of a very sad looking smoke detector that was partially melted by the hot smoke.
Good video. All I have seen of yours are very good. For whatever it's worth; "electrons" do NOT flow in the direction of the arrow on diodes and transistors. For electrons only flow from negative to positive. There is NO exception to this. Vacuum tubes proved this beyond a shadow of a doubt when they were first invented. What DOES flow in the direction of the arrow is "Hole Flow". This is a VERY hard concept to understand; when first learning solid state devices. Most of my students had a very hard time, when I taught this in technical school. But it is true. So what is "Hole Flow"? It is the opposite from electron flow. In that it flows from positive to negative. IE: it provides the "space" for the electrons to fill. No holes. no electrons can flow.. I write this, because in almost ALL videos concerning solid state devices; they show current going from positive to negative. That IS true but that is in reference to hole flow; NOT electron flow. For as above, electrons ALWAYS flow from negative to positive. Just the opposite of how the arrows are depicted on diodes and transistors. So in essence electrical "current" flows in BOTH directions. 1. Electrons from negative to positive. 2. Hole Flow from positive to negative. It is how one looks at it. For whatever it's worth. Keep up the excellent videos kind Sir and thank you.
I use conventional current flow theory since it's more confusing to people entering electronics when the diodes and other components point in the wrong direction.
You are absolutely correct. But it is sad that we must baby feed those who are not interested in the truth in this day and time. Again keep up the good work.
@@bigclivedotcom I support your policy and don't think it's dumbing down at all. A student may also struggle with the gravitational asymmetry when burger flipping at macdo....
That sounds like a plot device for a murder mystery show.
Stupid detective: "Why didn't he escape the fire, the smoke detectors were working?"
Smart CSI: "Yes but the killer removed the battery and blew smoke into the detector setting the new baseline tolerance higher than a fire."
Killer: "And I would have gotten away with it too if it weren't for you meddling kids"
ROLL CREDITS
I expect that unless you did that immediately before setting the fire, or maybe took the battery out, set the fire, blew a mouthful of smoke in and reconnected the battery immediately before scooting, they would eventually reset and recalibrate down to a lower set point. The way you would sensibly program something like that is to take the differential of the detected reflection level, as well as considering the DC level itself. Signal value rising faster than a certain cutoff rate, or the level simply being higher than a particular set point anyway (indicating an environment already so smoky or dusty that your detector hasn't a chance of working as intended) = set off the alarm. That then protects both against fires that are close by (causing the internal smoke density to rise quite fast), with the alarm going off even before the smoke actually reaches a dangerous level, and the more insidious case of a slower or more distant burn filling the air with smoke too slowly to set the detector off by rise rate alone, but reaching a dangerous enough level that if you haven't already picked it up by smelling it building up, or being awoken with a coughing fit, at a point where you could still safely escape, then you definitely need an audible jolt to get you out before you suffocate. With the additional case that if you connect the battery and the environment is already dangerously smoky, it will go off immediately... with the user then having the option of just taking the battery back out (as the alarm will trigger before you've even properly clicked the terminals into the connector, let alone put the lid back on), or taking heed of the warning and vacating the area.
And, well, if you had the opportunity to do such a thing, you could probably have just took the battery out, set the fire, then snuck back in afterwards to reconnect the battery. Or cut one of the cables right where it's soldered to the board (or desoldered it?), set the fire almost immediately underneath, and let the flames destroy - or at least heavily distort and disguise - the evidence for you...
@@markpenrice6253 Or just stick something to the ceiling with wax, enclosing the detector. Set fire, it's well established by the time the wax melts and drops the cover, and shortly any remnant wax will be vaporizing and the cover will be a nondescript patch of melted plastic on the floor, possibly intermingled with the remnant plastics from the detector body itself.
@@markpenrice6253 Or replace the battery with a totally depleted one.
Remember, life saving devices is ALWAYS the place where it makes sense to cheap out ...
Buy a dozen per room, for the same price 😭
And yet they have a place in poor countries.
That and military gear. Remember 'mil spec' means the same thing as 'built by the lowest bidder.'
Well it works better than none.
@@dutchdrifter8740 no, they don’t. Manufacturers make the name brand ones for about 5 bucks each, they then charge people 20-30 bucks for that same item. (statement is true for everything actually). Life saving equipment should be forced to be sold at reasonable markups. But this is a greedy capitalist society, so that’s not gonna happen.
I'm sitting on a couch at midnight watching a man take apart a smoke detector. WTF am I doing, who am I, and how did I get here. Great video, I think?
You’d probably enjoy more of Clive’s videos, they’re hilarious.
You're in the right place, at the right time. Just grab a whiskey and you'll be all set.
Well your name does your comment justice. Welcome.
@randonness productions: You're either really lame or wishing you had a better electronics understanding.
Something about long-form content with people talking over. I watch beekeeping videos for the same reason.
15:33 Do not change smoke alarm batteries while house is on fire.
That should be in the user manual :D
That's actually a poor design. What happens is there's a weak battery, the device detects smoke and starts alarming for a while, then the voltage drops underneath the operating threshold and it resets. Then it will remain silent rather than trying to alarm again.
@@straightpipediesel You ought to change batteries once per year. Furthermore, I'll assume blinkenlight pattern changes when battery goes low.
@@volo870 Most people are too lazy to. That's why California banned smoke detectors with removable batteries; they have to be 10 year permanent lithium type. Poor people were apparently not replacing and worse taking the batteries out.
@@straightpipediesel Why the hell would you buy a smoke detector then? It's better to rely on your smell and guts than on a malfunctioning device.
In my neck of the woods smoke detectors are VERY rare. But those installed are being taken care of.
The volunteer fire department I am on has always installed smoke detectors for free for the elderly and folks who can’t afford it. Otherwise we sell them for $5 US, which is our cost from Kidde Company. In America the first week in October is Fire Prevention Week and it’s suggested to change the battery out every 6 months which normally is around daylight savings time where we change the time of day either by falling back 1 hour or moving ahead by 1 hour.
The new dual smoke detectors we got earlier this year is touted as both photoelectric and ionization. I should send you one to dismantle and test.
Do it!
Thank you for your service.
Firefighters are heros.
The fire department here says test once a year and change the battery 6 months later. Also, you are supposed to replace your smoke detector every 10 years minimum. Kidde (pronounced kid-uh for those that care) now sells 9V batteries that they guarantee for 10 years in their smoke detectors. One detector, one battery, one decade. I also use a carbon monoxide alarm in my room and between my furnace and water heater.
Can't say I'd be wanting to trust my life to a 9volt battery anywhere near 10 years old.
If they're anything like our fire alarms the figure isn't far off, plus the thing doesn't die quietly. You will KNOW when the battery runs dry.
I really appreciate all the great information and explanations, I have always enjoyed taking stuff apart to see how it works, the circuit boards and what not are so confusing but i'm slowly understand how all the little do-dads work, great video! :)
Experimental Fun don't deal to bad, it's 3 A.M. were i'm at now. Try to go to bad early for work and this is what happens
+Experimental Fun
"I have always enjoyed taking stuff apart to see how it works"
For many years I did the same, and invariably ended up breaking stuff; but in due course I learned how to fix stuff and then how to make stuff.
Yup. I've taken apart tons of stuff I got for free from the local thrift store. If you find somewhere local that is already tossing stuff that doesn't power on, it's a great source for random parts and repair/troubleshooting/circuit lessons. Some second hand stores are even paying for hazmat recycling just to throw out electronics stuff. So your actually saving them money by taking the e-junk off their hands.
Eventually it dawned on me that my time is better spent learning with intentionally selected components where I know what I have, know that it works, and have spares readily available -if- or rather when I make a mistake.
It's still handy to have a bunch of junk boards laying around to reference to though.
Personally, I limit playing with junk box components mostly by the datasheet. If the DS is a page or few, it's worth goofing around with. If the DS is longer, that's the kind of thing I want new spares for. There's nothing quite as annoying as spending a bunch of time troubleshooting a broken part or breaking something after spending time on it without a spare on hand.
I also highly recommend trying to remove and reattach some more advanced surface mounted packages like QFN's on junk boards. It's very easy to assume "I'll fix this easily" just to learn the reason why rework stations are a thing.
I think the best stuff to salvage and study are power supplies. There are lots of cool things you can learn, and no matter your field of interest your going to need at least one power supply.
-Jake
@@infarno91 loop ll
Ah yes, this is the device that tells my wife when the toast is cooked!
That's probably the best use-case for it! i'm not quite sure i'd trust it as a safety device, but for analysing you wife's culinary talents, sure!
@@theafro well that does show it works so it's more like a reason to trust your smoke alarm.
Yep, the old *Cooking-Alarm!*
Back in the mid 70s I had a school holiday job working for a company that among other things made a photoelectric smoke detector. It was based on a tiny incandescent lamp, 2 CDS cells and an old 741 op-amp in a round metal can. This was before microcontrollers or dedicated chips. From memory it compared the detected light from 2 sensors via different paths in a black chamber.
Motorola made a dedicated chip back in the early-mid 80s MC14466 - a later version may still be available. I now work with a smoke detector that used a dedicated chip until a year or two back when the manufacturer changed to a 14-pin PIC micro. An op-amp circuit connects the IR sensor to the PIC. A lot more parts than the detector shown here, but still relatively low cost from the source.
If a ceramic cap measures 16uf it's probably 22uf "nominal" - cap tolerances are always negative,then you have the falloff of capacitance with DC bias
Or just reflow the solder on it and meassure "design" value?
"cap tolerances are always negative" - false. It depends on the manufacturer, and even then, expect 10% to be outliers. Source: I measured about 200 caps just to see for myself.
I believe the 4.7R is an emitter swamping resistor to keep the transistor gain constant over a wide temperature range, the B-E junction forward drop is quite temperature sensitive and would cause the LED brightness to vary with temperature. I would expect that would complicate the sensing threshold (and battery drain). A Mosfet would be a better choice, but needs more voltage.
I just bought a number of smoke detectors and did a little research to find, surprisingly, the Photoelectric type are actually superior in aggressive fires, where the Ionization type often take several minutes to respond in these conditions. They are also less likely to false with cooking vapors and such than the ionization models.
The Ionization detectors are the response time winners for smoldering fires however.
It seems a combination of the two might be ideal.
Thanks for all the great videos
So what if my house burns down? I saved $6!
If you have the money buy a more costly one but as a student i.e. a cheap one is better than none at all. You saw the circuit they came a long way and chinese slave markets made it possible to have quiete good ones for 10 bucks or less
Result !, Oh wait...….
benni5541 consumers prefer China slave labor products
How crazy simple does it get? I like that little chamber. Simple and cheap design.
bigClive: "I didn't want to put out too many similar videos" That is quite literally the opposite to most youtubers, THANK YOU!
all these "potential" dividers . . . how long do i have to wait for them to become real?
If you drop them, they become kinetic dividers.
Cool video! I take apart old/faulty ionization type detectors for the Americium-241 sealed sources. I have a lot of sources, because radioactivity is my favorite hobby. Am-241 is a great alpha particle and low energy gamma source. Many modern ionization type detectors also have a photoelectric chamber too. Older industrial ionization type detectors used a higher activity of Am-241, usually with two separate Am-241 sources. One stronger source would detect smoke from early fires, and a second weaker source in an enclosed chamber for intense smoldering fires. Anything that passes between the Am-241 source, such as a gas leak, or even very high humidity has the potential to attenuate the alpha particles, causing a drop in the current and triggering the alarm circuit.
Fife Council considers smoke detectors an investment - better value than sending out the fire-brigade - and will install them in your house free, so "cheap" isn't needed here.
Many of the fire departments have teams that will fit them free too. But the downside of that is that if they reduce the number of fires they get their funding cut. Because that's the mentality of politicians.
It is still the same number of fires with a lower amount of fatal casualties. Stopping funding would be mad. Certain British politicians do not seem to be interested in serving the public interest or common good.
Simple answer: Don't vote Tory.
Come to rural America where you have to pay a yearly fee or the Fire department will just let your house burn down.
www.npr.org/sections/thetwo-way/2010/10/08/130436382/they-didn-t-pay-the-fee-firefighters-watch-tennessee-family-s-house-burn
Even if you don't need them as actual life saving measures, you could use them for... Let's say hacking in some smoke-triggered automation. Wouldn't mind adding this and a latch relay to a 3D printer or something.
It works very similar to how a surface scatter turbidimeter works. They create a smooth pool of flowing water, a light shines on the surface and is reflected off into a cone of non-reflective paint. Only particulates in the water reflect light into the sensor. The beam shines at the water at about a 60 degree angle, so the light reflecting off the water goes equal and opposite. The sensor is 45 degrees off the water however, so it only sees particulate reflections, not water reflections.
turbidity is a good word
a what?
Surface scatter turbidity monitors are routinely found in clean water treatment plants where they are used to monitor drinking water quality, which in Britain is tightly regulated. Turbidity can be loosely described as cloudiness, which at high levels is unsightly, and can indicate contamination.
You're actually the best youtuber to learn the basics of these things thank you!! Sad that i didn't find someone like you in the past 8 years of experience in electronics...
Thanks Clive. You just reminded me to test all of our genuine UK British Standard smoke detectors.
I should have added that at the end. "Remember to test your smoke detectors."
"Take up smoking" doesn't resonate anymore.
change batteries once a year nuts if they need them or not...............with good quality ones
Love this channel Clive. Only just found it a few days ago. Very interesting, and it keeps me from doing what I should be doing at midnight; sleeping.
The red LED on my smoke detector pulsed when he mentioned it. Creepy!
4 $? ....they must be holding a fire sale!
::groan::
Get 'em while their hot.
A smokin' deal !
Ba-dum tish!
Baby You Light My Fire LOL
Fascinating! The most interested I've ever been in a smoke detector...
I used to work in that industry. The MSP430 family was actually a common ish choice for optical smoke detectors due to its great low power modes and rich ADC options. However at least the engineers I knew of eventually moved back to an ASIC solution - so the cost benefit is right on the edge.
BTW in some instances the device may not go to lobat mode unless it sees VBat sag when load is turned on - in this case, the emitter LED.
Good video! It was a big relief when my local council installed mains operated smoke and heat detectors. You do sleep better, what with so many lithium based products laying around, many on charge while we sleep too!
The year 1921: Cinema fire caused by motion picture film. The year 2021: House fire caused by lithium ion battery in thermal runaway... One step forward, one step back... The thing in common is both have their own oxidizer.
I have 2 FireAngel ST-622 alarms supplied by my fire brigade. These are supposed to have a 10 year battery life. Both now are giving a low battery alarm after only a year or so. The batteries are not replaceable. Took one apart and the battery was still good. Contacted the manufacturer and was told to contact the seller.
11:01 the lines in a transformer symbol are supposed to indicate the magnetic core material (iron or ferrite). The odd power rail routing may be an abandoned plan to detect board damage or just incompetence.
John Francis Doe It really does not matter in this case as it is just a rough and dirty drawing to convey the basic logic behind the circuit, which is all that is really of importance in these discussions. What surprises me far more in this example is that they got away with the far off filter capacitor as most low dropout regulators tend to be very particular about placement location and the ESR of their filter capacities lest they go into oscillation.
Clive, the big scare is that so little is said about the fact that even the best ionization detectors (which are fastet to respond) go dead in 7-10 years, and just changing the battery won't fix that. New detectors with a built-in 10 year battery fix that, toss and replace the whole thing. It costs less than 10 battery changes and won't wake you up 10x in the middle of the night.
Canned smoke, for a real test, is worthwhile for all of them.
Photodetector alarm for 4 bucks? Priceless!
Yeah, I like the idea of the decade smoke detector. Now if only they had energy budget for WiFi or BLE for ten years...
If you want the alarm to be sent out over bt or wifi, it only needs power once when you configure it, and once more when there's a fire. But the radio chips add $5 even to cell phones, which means $10-20 more in the retail price. Ante up.
I've got the BRK ones with an RF base wired into the house lighting circuits they all have 10 year lives, and Li batteries for backup. They are the ionisation and optical ones. Since I had to fit mains interlinked alarms when I built a new house extension to meet building regs it was easiest to do it this way and I can fit extra ones or replacements in a matter of seconds. Recently bought 2 spare bases from a closing Homebase for £7 each. Newer UK houses will all have mains detectors so these battery driven ones will be of little or no use in them.
I smashed my smoke detector nearly 20 year's ago.
I recommend changing smoke detectors completely every five years. They do accumulate dust. In greasy or dusty areas they should be changed sooner or a rate of rise detector fitted.
I'll admit, there's an elegance to the design that appeals, in much the same way there's elegance (if you know where to look) in a Trabant. Elegant or not, I'll still not entrust either with my children's wellbeing!
Cheers Clive!
Buying smoke detectors in bulk, we spend about $300 for about 15 of them, minus batteries.
They're good for 10 years (again, minus batteries), so for about $50 a year for all of them (including batteries every year) ... it's well worth the price for the safety!!!
Ours are also hardwired with battery backup, so they normally run off the mains. And they have an alarm wire, so when one goes off, the rest of them also start beeping. Makes quite a racket, LOL.
The zener diode that is missing is meant for the micro controller to get more of an accurate voltage reference of the battery state and sound a low battery alarm even when ran on stable the mains power, this smoke alarm can't because it has a voltage regulator blocking the actual voltage reference of the battery.
Normally test benches are used for simulating logic controllers, so you dont have to programm the chip itself, but you test your code in the testbench and if you tested it throughly you can start with your prototype in the hardware.
Same way it is done with using field programmable logic arrays for describing the hardware, simulating and testing it in a testbench and then you can put that into a one time programmable chip
Great video!
There is a RUclipsr named David McLuckie who did a teardown video covering an even cheaper smoke alarm he found online (On AliExpress). That one was tested with a simulated fire and appeared to fail to operate. What he found inside was a much smaller circuit board than the one looked at here which looked as if the only thing on it was the detector itself until David pointed out a tiny buzzer. The scary thing is, apart from a lack of battery cover, it looked just like the one torn down in this video and the detector Clive tore down in 2015.
Irrespective of your negative comments the engineering design is very interesting and represents a totally different take on design and minimising costs. Just think, no dangerous radioactive isotopes around.
I design PCBs using Cadence /Orcad and when I think I have optimised the design we send it to a Chinese design house that reviews our work. It is amazing the cost savings they come up with. We save a fortune every year implementing their suggestions.
Chinese designers have different criteria to other cultures - which is why so many leading Western countries do initial designs and, ultimately, production there.
The optical detectors are widely available, but often use a dedicated chip that can test the chamber for functionality by detecting low reflections of test pulses. It also differentiates between temporary dust reflections and smoke, and also has proper low battery warnings.
The cheap units (only marginally cheaper that the real thing) have debatable detecting ability, can drain the batteries fast and not warn about low voltage. Some have sounders that are as loud as your microwave oven beeper.
They're basically fake smoke detectors.
Clive, I think the purpose of the 10uF and 1K resistor is to have a low current charge and high current discharge. The life of an alkaline battery can be 2x to 4x longer at lower current discharge rates.
Surprisingly the standards do not allow a mute function. If it's done properly the sampling can be done less than 10s. Smoke should be detected before it is visible. This circuit does not have enough gain to allow to much contamination build up. Cheap chambers can melt with heat before the smoke is detected.
This meshes well with Tom Scott’s newest video today on the history of fire departments.
The algorithm working well and recommended this to me after watching Tom's video too
For some reason this video reminds me of the time I was stapling up a cloth on a wall. On the other side of the wall was a smoke detector. The vibration from the stapling must have done something but the smoke detector caught fire, but luckily alarmed itself before it died. It's very ironic when smoke detectors catch fire.
That's funny
Clive should start a podcast
I have a dual-mode detector and I change the whole unit every year.
I love my life and its worth the $25-$30 a year for me. I pretend I spent that money having a few beers in a pub, and I don't even drink!
I would add another every year if I was that paranoid just because it would be fun to cover the entire fucking celling with those red eyed blinking boys.
Perfect gift for your mother-in-law.
Classic Clives never age. They are as interesting now as they were when first aired. I enjoy watching them. 👍
You can see the flashes from the LED again at 16:38 for a few seconds... and a couple more times later on... so the camera may be shifting around a bit with the focus, etc. Interesting little unit... and nice to see those 3c micros in the wild! Hopefully more people start talking about them and see them become a thing of interest for DIYers... no excuse not to use a micro for 3c! ;)
This makes me think that the free smoke alarm the fire brigade put on the landing a couple years back is an optical one, cos it triggered when I was messing about with my smoke machine, the old alarm didn't do such things cos it was a nuclear reactor type, or whatever it is with the little Americium bit in it... :)
The nuclear reactor type is an Ionization smoke detector.
twocvbloke The other type is an ionizing detector. The best smoke detectors contain both optical and ionizing units as each has its strength and weaknesses, what one detects earlier the other takes longer and vice-versa. But most of the less expensive detectors are optical and they are very good at detecting fires that produce a lot of smoke while the ionizing detectors are better at detecting slow smoldering fires and the combustible gasses they give off well before they have produced much detectable smoke - so one is great at detecting slow simmering fires and the other fires that are fast burning and/or produce a lot of smoke (or steam, even).
Ethan Poole the landlord put a small rubbish battery powered one on the ceiling in the kitchen a few years ago, what is that one? Its over my gas cooker, it's fine if I use the oven but when I boil things in water on the hob the bloody thing goes off, it's done so twice this week once with rice and once with a boiled egg, I had to take the battery out with the egg as flapping a towel at it didn't shut it up. Is that the steam or the burned gas
All smoke detectors will detect fog. In theatres they have to use heat detectors or use a temporary bypass system during a show.
the latter sounds scary. I regularly visit Theatres
I was working in a hospital once. The builders had covered up all the smoke detectors to prevent dust ingress. On the day of recommisioning, the had reenabled the zone detection. As they were removing the covers, the elasticated cover flicked dust up into the detector and set of the alarm!
Adam Bryant see that in my hospital too usually stuck a rubber glove over them.
Interesting! It may work but your warning is correct. In the UK (and Europe) you should only install smoke alarms certified to EN14604 standards.
NB I have no clue of what I'm talking about but I was thinking that maybe the idea behind the detour to connect that capacitor was to keep an option open for connecting multiple smoke alarms in a network. Where the electrolytic capacitors would be an endpoint for the transmission line.
The spring on the LED is a brilliant bit of design for manufacturing.
If you have enough memory , after your first program you can overwrite everything to 0 , usually means NOP and program new application from there on. Not having to just bin it straight away.
I bought a Smoke Detector for $4.50 at a retail store Wal-Mart. Lit a fire on top of it, never went off until I poured water on it.
I test my smoke detectors by throwing then into a fire. They usually don't go off, so they were obviously no use to begin with.
At 10:40 that should be a thyristor and not a bipolar transistor. As this should be a latching circuit, although there is no reset switch for some reason.
What the heck is that symbol on the PCB? The circle NB with a dollar sign with devil horns?
I wonder if fast pulsing is because it;s looking for a rise in light from pulse to pulse rather than absolute level. Probably not good for battery life though
A previous unit based on a dedicated chip pulsed slower, but woke and increased the sample rate if it detected something suspicious. Maybe this one was in a heightened alert mode. I might wire in an extra LED with suitable resistor to allow monitoring of sample rate in a more realistic way.
I would suggest it's looking for a high degree of match to that pulse in order to weed out false positives, changing up the rate would only help that aspect.
What a great explanation. Very interesting. Thanks a lot.
Nobody buys a 4$ smoke detector for their own home. Landlords buy them.
I'll bet that besides Big Clive, most people who buy these buy them in packs of fifty.
In my experience landlords just don't replace them even 50 years later as long as they work. I did not trust the ones in my last apartment so old they made a buzz not beep which took us an hour to realize one was going off below us...and did not even have battery backup. Lease says they can not be removed or modified so I installed my own new name brand alarm adjacent to theirs.
Code will probably require hardwired interconnected systems for rental units. These are for people who want the security of a smoke alarm, but only want to put a fiver toward their fire safety budget.
Oh, and the cost of a warranty is not included here. Even more expensive "cheap" smoke alarms have high failure rates. They come with a warranty though, which you are paying for in the price. Part of the $13/£10 you are paying is going toward sending you a new one when it breaks in 6 months.
Yep slum landlords.
Dishonest landlords.
Cheapskate landlords.
Or people that just want to collect the insurance when the smoke detectors don't work.
Need I say more don't think so.
Thankfully in Australia (or at least the state I am in) has laws requiring landlords to have proper smoke alarms (and my landlord recently send a guy out to check the smoke alarm for compliance)
Andy Lundell, if they do they probably take the batteries out the first time they false alarm, like when they've burned their toast. I have a full fledged commercial Fire alarm system, but that's only because I designed it when I worked for a company that made them.
4:12
You sound like you're speaking from experience
Sounds like story time!
My best was when I emptied a lunatic asylum accidentally. I was working on the alarm system and it went off. The system used a huge air-raid type siren on the roof and my legs literally went like jelly when it went off.
@@bigclivedotcom ohhh god that sounds horrible XD I'm surprised you can still hear
Air raid siren in a lunatic asylum? That's sounds like Broadmoor! They are talking about decommissioning their former WWII air raid sirens - it would be amazing if they could send one to you for a tear down.
@@bigclivedotcom Reminds me of the time when I was working overtime, during the weekend, alone in a data center. Which was not known to the guys who thought it would be empty during the weekend, for their test of the fire suppression system. I was not aware of them and they were not aware of me.
The fire suppression system just flushes the room with CO2. The ingenious part is the acoustic alarm.
The high pressure CO2 enters the room through a klaxon. Extremely simple, extremely effective and extremely right behind me.
It was so shocking that I was paralyzed and couldn't muster any clear thought for a few seconds.
According to eevblog there's an in-circuit emulator in the development software kit.
Not in the software kit, available as a hardware kit :D
Not all electrically programmable ROM is UV erasable, some technologies are physically irreversibly altered.
If they are using eprom rather than fusable links then it may be possible to erase them using soft x-rays.
It could. It would depend on finding xrays with high enough energy to penetrate the plastic but not so much that it causes damage to other devices within the chip.
My landlord had a few smoke detectors mounted in my flat, since they are now required by law. I took one off to have a closer look, and it was also one of these optical jobbys. What surprised me was that it actually had a replaceable battery (of some weird uncommon format), while these devices were clearly rated for 10 years of battery life and then to be disposed of - not the battery changed. So I wonder if there are some things in such a smoke detector that age and make it so that it doesn't detect the smoke any more after such a long time, since if the battery is replaceable, you could just replace that and keep the unit?
You do get dust and dirt building up in them over time. Especially when near a steamy or oily area like a kitchen. It's a good idea to replace them fairly regularly.
Related to 13:00, while the circuit is not relying on the 4.7 ohm resistor being in the emitter for limiting the current, it seems to me it would not do much at all anyway in that role - assuming a 3V control signal from the CPU, by the time the emitter would raise to 2.4V, the LED would be passing a full 0.5 amps if the 1K wouldn't prevent all of that in the first place. Is 0.5A a typical absolute maximum pulse current rating for IR LEDs...? :)
Infrared LEDs are often rated at a peak current of an Amp or more and often driven in pulses.
Oh. Okay then, it _is_ actually doing something limiting the discharge current from the capacitor...
Is the zener just extra protection for the microcontroller 3.3V supply (prevents overvoltage in the event of regulator issues or external EM interference) ?
The older style smoke alarms had some sort of dedicated 14 pin chip which monitors in pulses, the change in resistance between two terminals (plates) with a trace of uranium of some sort placed in between the plates that reacted to smoke.
Do you know why smoke detectors use relatively low capacity 9v batteries instead of higher capacity AA or AAA? Is there something about the sensor or buzzer that requires higher voltage?
Well, in my country they use 4x AAA batteries, so there is probably no objective reason for that.
It really is fascinating how these fire alarms work. I've always wondered how they work.
There use to be 2 types. The ionisation kind which is interesting since it contains Americium 241, about 0.3 ug (I think), which comes out to 0.9 uCi. It is an artificial element. It is somewhat fissile, which means that you can make a nuclear bomb with it, if you can collect about 10 to 20 kg.
The other type is the photodetector type.
A new one on the market is heat detection.
Couldnt they have built it inverted? So the receiver always gets hit by the transmitters light, and the receiver measures the lights intensity. When there is smoke, less light is received and sound the alarm.
Does it have any low voltage warning mechanism or not? I also bought one of these. It didn't appear to have any low voltage warning, so I stopped using it.
i hired the "eh ehm... excuse me!!" lady you find everywhere while you light up a cig, no maintainance
and honestly you need a really clever algorithm to tell if it's really smoke or whatever else, that transistor amplifier looks really lame, or maybe it beeps just when the heroes jump off, with an explosion on the back
Does the test button just send a signal to the microcontroller that turns on the peizo, or does it turn the LED in the chamber up to full brightness to check that it is detecting?
(In the same way the test button on an RCD mimicks the fault condition, rather than just switching off)
I'm not sure if this unit does test the operation of the chamber.
what is the best way to detect fire and do fire detectors have any kind of standardized tone or beep rate
I wonder if, once it calibrates with smoke in the chamber, if the smoke is been removed and several minutes later added again, will it detect it?
Pro tip: if it has a battery and yells at you, it's a smoke alarm. If it's hooked into a big system with a fire panel, it's a smoke detector.
I'm tempted to make my own videos like this.
With my vast knowledge of, "not a lot"
Early videos would be vast and incomprehensible.
Can't verify it, but the 10Meg resistor with the transistor (and the suspected photo diode)? My guess is that the transistor is actually a FET and the 10Meg guy is its pull-down. That would create a nice logic level (vs. an analog signal) at the output though.
1:07 “… and we’re in like Flynn!”
Why is the output from the piezo transformer referenced to the +9V? Any benefit to reference to 0V or floating/isolated??
Hmmm...the photo detector side has transistor-beta-dependent gain. So exact photo current required to make the “CPU” signal go LOW is dependent upon the transistor beta. That makes “zeroing” the residual light somewhat tricky. What am I missing? Perhaps “CPU” signal goes into an A/D converter and further analysis is performed by the microcontroller.
I think the real things do use an ADC.
Very intriguing
I've got A xiaomi smart smoke alarm. It's brilliant. Keep me upto date on if it's working or not, and let's me sail down the sensitivity when the kids are cooking, and it will ramp itself back up in a give time.
Plusr it has a hub, that other smarts hang off, which I keep in the bedroom, at also sets of ab alarm, and flashes red.
Probably a bit pricey if just being bought for a smoke alarm, but cis I wad already using the xiaomi mija hub, it took a punt, and been happy with it.
They cost less in a LOCAL store and it will be at least somewhat safe. Not that it matters because as soon as they start to warn the battery is empty they get pulled out and not replaced
At least this has a microcontroller. I have one on my possession, not autonomous but connects to a fire alarm panel, that the only IC it has is an HEF4013BT that appears to be a dual D-type flip-flop. It's diagram is much more complicated, with a lot more transistors but I don't think it has the required functionality. A lot of false alarms by these fire detectors and they are not made in China but in Spain.
It sounds like it may be based on simple voltage threshold or transition circuitry. A processor allows better filtering against nuisance alarms from slight transients of dust or smoke.
Here's wierd question,, it's seems like it would take a while to detect smoke, with optical sensors, because the smoke has to creep into the plastic housing then creep into the sensor housing. Like I would think you need a fan to suck smoke Into it?
Some industrial ones do have sniffer pipes that pull air through remote detection chambers. But in a home, smoke will diffuse into the air fast.
@bigclivedotcom ohh ok, I was thinking like a stream of smoke at first, but in a closed room, I get it now. I'm only a amateur level tinkerer, so I find your videos are the best at explaining how all these electronics work. Thank you all the way from 🇨🇦.
If that is the chip that Dave showed the website for, or one of their models at least. It has a full blown development environment complete with documentation down to timing diagrams and translated engineer notes. When I seen that I was surprised by the level of support by the vendor right out the gate. Some of the info when he was flipping through on his video you don't need to use the chip but would want to know to really squeeze out a lot of work.
It's really odd to see a chip like that with good English documentation. I've been reading through its PDF and it's very readable.
Definitely, even from a coders perspective it's better than most API documentation.
Spontaneous combustion : camera trigger - or : Smoke-ER detector - or - _Vape-ERR_ : catching fire - detector *_R > G_*
8:03 maybe in combination with the capacitor a voltage divider?
If the capacitor is after the switch is it there to cause the delay in the test button?
9:02 Maybe they needed some kind of inductance there? It doesn't make a lot of sense (why would you add an inductor?) but having such a roundabout wire might add some inductance.
I have the same but i change adjust potentiometer to multi turn for better sensitivity adjust and add switch in front to turn off and instant discharge electricity for alarm.
no mute button? so if you're coming out of the shower and that thing starts beeping you have to take it down and take the battery out. then you'd never hang that back
Most fire brigades in the UK will fit smoke detectors for free. They are the FireAngel devices which would otherwise cost around £10. They have a 10 year guaranteed life Li-ion battery which does not last 10 years. When the battery runs out and it starts chirping you phone FireAngel and they send you a new one.
a very very very interesting explanation as usual
That light chamber looks exactly like the one in the Nest smoke detector I autopsied a while back after it got a mind of it's own.
The main difference being the Nest alarm probably packaged the same sort of components with a $399 price tag, rather than the $3 Clive paid! ;-)
@@ddragon8154 I will say that the nest seemed very well built inside. Although it's the only smoke alarm I've ever owned that has actually failed.
+Do R/C! A lot of times people miss smoke detector failures because they don't test them often enough. Assuming that smart detectors can run a thorough self-test and report faults to the user right away, it's one of those few cases where having domestic tech connected to the network is a *good* thing! :-)
Watch the video based on the title thinking there was a way to torch my place for insurance without incriminating evidence lol.
Is the zener diode used for “low battery” detection?
Everybody's on the 3c controller this week!
ruclips.net/video/VYhAGnsnO7w/видео.html
The manufacturer's website appears to have Multi-Time-Programmable controllers too, they're marked as MTP on the "Catalog" links. Can't find a supplier though.
Yeah. Mike mentioned it and inspired us. I put a link to Dave's video in the description.
so I am at risk of getting crispy because I was smoking when I changed the battery?
I'm kind of curious as to what vaping device you're using to test the detector with? Seems to be something a bit more substantial than the EGO style devices you usually use.
It is. I bought something a bit beefier. A Kangertech.
Nice, which model?
44CT232 I'm interested too.
Too late, my uncle's house already burned down just a few weeks ago. The investigation is not yet complete, but they are honing in on the photovoltaic solar system!
I did get a picture of a very sad looking smoke detector that was partially melted by the hot smoke.
Good video. All I have seen of yours are very good.
For whatever it's worth; "electrons" do NOT flow in the direction of the arrow on diodes and transistors. For electrons only flow from negative to positive. There is NO exception to this. Vacuum tubes proved this beyond a shadow of a doubt when they were first invented.
What DOES flow in the direction of the arrow is "Hole Flow". This is a VERY hard concept to understand; when first learning solid state devices. Most of my students had a very hard time, when I taught this in technical school. But it is true.
So what is "Hole Flow"? It is the opposite from electron flow. In that it flows from positive to negative. IE: it provides the "space" for the electrons to fill. No holes. no electrons can flow..
I write this, because in almost ALL videos concerning solid state devices; they show current going from positive to negative. That IS true but that is in reference to hole flow; NOT electron flow. For as above, electrons ALWAYS flow from negative to positive. Just the opposite of how the arrows are depicted on diodes and transistors.
So in essence electrical "current" flows in BOTH directions. 1. Electrons from negative to positive. 2. Hole Flow from positive to negative. It is how one looks at it.
For whatever it's worth.
Keep up the excellent videos kind Sir and thank you.
I use conventional current flow theory since it's more confusing to people entering electronics when the diodes and other components point in the wrong direction.
You are absolutely correct. But it is sad that we must baby feed those who are not interested in the truth in this day and time.
Again keep up the good work.
@@bigclivedotcom I support your policy and don't think it's dumbing down at all. A student may also struggle with the gravitational asymmetry when burger flipping at macdo....
Hi clive, do you take donations for dissasembly?
Is there a relaible detector that is known for DIY-projects that use a ESP32 to get the detectors connected over wifi?