Was this the first LED test light?
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- Опубликовано: 6 сен 2024
- This is the circuit board out of my first multi-voltage tester when I was an apprentice in the 1980's. It was quite an expensive unit at the time, but is designed for professional use.
The circuit seems simple enough with just a single sided circuit board and traditional through hole components, but it was an arduous thing to reverse engineer due to the very weird way the components are used to achieve a lot with the components of the era.
There are two distinct sections. The simple two-LED polarity indicator with PTC resistor to regulate the current thermally, and the main section that does devious things with standard transistors.
I think the PNP darlington is used to provide more current to the 12V LED, which has its own circuitry.
The 39V zener seems to be capping the LED-transistor supply to protect against overvoltage. The LED transistors themselves are being used in a non-standard way that possibly allows them to cascade progressive LEDs in series for maximum intensity at low current.
The LED supply is created by a fixed 120K resistor in parallel with a PTC thermistor that allows higher current to flow at lower voltages, but thermally regulates the current down at higher voltages.
In the future I'll reverse engineer a generic Chinese multi-voltage test light to see if they have copied the circuitry from what I believe to be an original Steinel design.
If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:- www.bigclive.c...
This also keeps the channel independent of RUclips's algorithm quirks, allowing it to be a bit more dangerous and naughty.
#ElectronicsCreators
Wow, only 6,000 subs for the MILLION. Great work Clive. You deserve it.
😮
Though it’s probably fair that we’re all subs for BIG Clive. ;)
needs another fanny flamboux viral video 😂
@@eliotmansfield maybe Mr Bunbun can have another tragic Easter, he hasn't had one in a while
Can't believe I've been watching him since he had under 2000
Now only 5k and counting :0). Agree, well deserved Clive. Hope there is a 1Meg Review Special.
Big Clive, I just reverse engineered a very small USB charger board. I now have a deep appreciation for your work. There is nothing easy about doing this. Even on this tiny board, it was very difficult to do. So, A Giant Thanks for the hard work you do for our entertainment. God Bless ..
It can be deceptively time consuming.
@@BigClive ... but also intriguing in a detective mystery way!
@@BigClive
Good for the mind and reducing Dementia etc..
An amusing thing to do is make a crystal set radio completely from scrap things as they did in WW2.
The other is making a wind turbine that will charge a 12 volt lead acid battery.. also mainly from scrap parts.. a few pointers.. converting a car alternator does work with small magnets but low power but even with big neo magnets the spin speed/power required is just too high..
Axial Flux does work.. look up Tim Piggot .. big wooden blades and fibreglass casting the coils.. these produce several/lots of KW .. a much smaller 16v 16A peak, about 300w output max is the Rutland 913/914 also Axial Flux.
Building a charge controller and possibly an MPPT .. I ended up buying mine.. (photonic universe in UK) the MPPT is a dark art of electronics.
The leaning curve in various directions is wonderful..
A word of warning.. it's not a quick build.. and also when you make the blades you will be tempted to test them .. they can quickly become the weapons of doom.. good fun though.. (big coat, gloves and chainsaw helmet recommended) and when you do finally put it up ... there's usually no wind for weeks.. Have fun.
@@BigClive 'tiny' stuff can sometimes be the worst!
One of my old nemesis... transistors in emitter follower configuration. It appeared to me to be using the LED's, the voltage divider resistors and the BE junction of each transistor in concert. Seems like that would be a mathematic nightmare to have designed it on paper first. You may have something there to suppose that they just ballparked it on paper, then breadboarded the circuit and then adjusted the base resistors (perhaps with pots). Like television circuitry, adjusting one would affect all the others. What a 'cluster'! 😏
I love the state of the Deathdaptor!🤣
That was just one cheap power supply that didn't even make it to the start of a video. It literally blew up in my hands when I plugged it in.
Its a nice change seeing a schematic without a chip, but it hasn't necessarily made it any easier to work through.
The more I look at it the cleverer it gets. On the left is a potential divider with mostly resistors, on the right a series string of LEDs. For all intents and purposes we can assume the LEDs have a fixed voltage drop, but the taps on the potential divider all rise together. The surprising thing to me is that the logarithmic scale indicated by the LEDs might actually be required for the device to operate properly, because as the voltage increases you need each potential gap in the divider to be smaller than the last one (so a bigger increase in voltage at the probes is needed) so the LEDs light up in the right order... Really confusing TBH.
Anyway, in case you're not familiar with transistors being used as they are here, this is a classic example of what's called an emitter-follower configuration (if you were using MOSFETs you'd call it a source follower). The name explains very well what it does: the emitter's voltage will "follow" what's being applied to the base, minus the transistor's threshold voltage. The advantage of doing it this way as opposed to connecting it directly is that very little current is drawn from the base, so it doesn't influence the voltage from the potential divider that much. That makes it easier to calculate what those resistors need to be and also means that the LEDs come on in discrete steps, instead of turning on more gradually. They also happen to function as diodes to prevent the current from going back into the potential divider at the step below and messing stuff up that way. Elegantly done.
Arrrg, so much going on in this circuit with the potential to affect other parts of the circuit! A key element is the BC546, which Big Clive identifies as "turning on" at a particular threshold. However it is actually configured as a current source, set to somewhere between 25 and 45 mA (depending on gain of BC546, drop across the 10k base resistor etc). That means the transistor is not necessarily saturated and instead permits the chain of LEDs to float at a voltage set by the emitter-follower action of whichever is the uppermost turned-on BC237B.
Bottom line: the key entry point to understanding this circuit, and which direction that action flows, is to identify the action of the BC546A -- switches on/off (VCat VSAT when on), or instead behaves as current source (VC very compliant to connected LEDs). Then all the rest can be understood step by step as you describe.
@@Graham_Wideman Yes, that's exactly what it does. It is indeed a current source. Or current sink, to be more accurate. That said the gain of most transistors including the BC546 is high enough that it doesn't usually matter. Gain also tends to vary within quite a broad tolerance so you usually don't want to rely on it that much. I tend to look at that configuration as yet another emitter-follower that drops most of the voltage coming in through the collector to a fixed voltage coming out of the emitter, which the 270 ohm resistor then translates into a fixed current. I suspect the 10K resistor is mostly there to stop the transistor leaking too much current away from the 12V LED when the first LED in the chain hasn't lit up yet and isn't providing current to the collector (because when that happens the current coming out of the emitter can come from the base instead). Other than that it's probably not that important.
@@ManWithBeard1990 Well the 10k base resistor adds quite a variability factor, because according to datasheet, the BC546 gain varies from 110 to 800, so each 10mA of IE/IC/ILED will result in IB between 0.012 and 0.1 mA, so worst case 3 to 4V across the 10k, acting to reduce IE/IC/ILED. The LED current could vary by about a third depending on sample of BC546 -- a little shabby.
@@Graham_Wideman I'm not sure I understand. I believe the 270 ohm resistor is what's meant to be limiting the output current, although you are right that 10K is a bit high for the effect of the transistor gain to be negligeable. Is that what you meant?
@@ManWithBeard1990 Yes I agree -- I assumed we'd already established that the transistor and its emitter resistor are in "current source" (or sink if you like) configuration. In that configuration, you ideally depend on a solid reference voltage at the base to set a solid emitter voltage which sets a constant voltage on the emitter resistor and hence the constant collector current. But in this circuit, the base does not sit at a well-established constant voltage due to current in the base resistor. I think you did get all that, just clarifying.
An interesting and cool find. I love the complexity and simplicity at the same time - all discrete transistors, none of that microcontroller rubbish.
I love that it is transistors and NOT a regular logic ic like some cheaper ones use when i tore them down
....for those of us playing along at home.
..😂
Here's a shot for all you discrete transistor fanboys.
@@chitlitlah It's always good to see trannies flapping around in the breeze.
What's this??? No microcontroller? No charge controlling chip? No USB connector? I LOVE it! Strange yet elegant in its design. Thanks for presenting this! You find some of the coolest stuff, and I love seeing what you'll bring us next.
agreed
Every even trivial EE job starts with an Arduino, gramps.
Elegant but not so simple as it looks. Even the bug C was a bit baffled by some of it.
@@edwardclarke3601 Very true!
I love the 'bridges' on the schematic. So used to 'dots and crosses' in cad, but I still draw my hand drawn diagrams with hump back bridges as well. Takes me back to the Maplin catalogue when it was 2" thick.
I rigidly keep humps as there's no doubt. It gives clarity for my head when working it through as well
I always keep the humps when drawing up CAD wiring diagrams. It's so much easier to understand and no ambiguity as to whether the designer forgot the dot or not.
@c31979839 I still like to use wwws for resistors, and bulbs with squiggly filaments 😀
Its how I was tought to do them at school and I've never had cause to draw a circuit diagram since (shame!) so its nice to see them again.
Worth noting that these voltage indicators have a work cycle of around 30 seconds measurement and 5 minutes cool down time due to the resistors heating up. They are not really a substitute for a multimeter but work well enough to give a go/no go indication in harsh high vibration environments where a multimeter movement might be damaged. Not really a problem with digital instruments. Better than a neon screwdriver or one of those battery powered voltage probes, but not by much. The main advantage is that it doesn’t require batteries and it can detect voltages from around 8 volts to 600 volts and give a clue whether to expect just a tingle or instant death.
They are mandated here in Germany to ensure the absence of voltage on lines in favor of a multimeter because of two reasons
1. They provide a load. Most Multimeters have 10Megohm input impedance and will measure just garbage with capacitive coupling of wires in the wall
2. They can only measure Voltage. If your Multimeter is in the Amps range without you noticing and you for instance measure a light socket on a ladder, the bang and arc flash will let you fall down that ladder
These things are not versatile and not accurate, but they don't have to be for that one particular usecase
I always carry testlights AND a multimeter
@@Fluxkompressor I work for a Dutch DNO, and the standard equipment is a Benning Duspol.
@@Fluxkompressormandated here in the UK also, for proving isolations.
The LED chain on the right is 2V each step. The middle transistors will switch on when their base is 0.6V above their LED voltage (apart from the last with the diode). The bottom right transistor is a constant current sink. The chain of resistors on the left will be carefully chosen to switch the transistors on at 2V intervals (apart from the one with the diode). Very clever.
That's exactly how i was working out how this thing works... 👍🏻
I think the steps between the resistor divider chain are larger than 2V.
But what is the 4V7 zener for, or the darlington, or that extra diode above the 24V LED?
@@MB-st7be The extra diode is probably being used purely for its 0.5V drop so the base of the lowest transistor needs to be a bit higher than without it.
Yes but why, why did it need to be higher? @@jam99
Love the scorch marks on the “deathdapter”!
For something as analogue as this it would be interesting to see it modelled in SPICE or similar and to investigate exactly what is going on
Yes, or simply use an analog computer -- ie: the circuit itself, and plot all the interesting voltages versus input voltages. That will illuminate what behavior each component contributes as input voltage progressively increases.
Old school and very clever! Some great stuff was designed in the 1960's and 1970's before affordable u-processors were available. I knew a few designers of this sort of stuff early in my work life and they knew RC network theory, transistor logic, and PCB capacitance effects inside and out. Liked seeing this device! Cheers.
Absolutely.....just look at the wizardry used to make analogue colour tvs work !!!
Reminds me of the LM3914 that was used in lots of projects in electronics magazines of the 80's
LM3914 and its brother the LM3915 (log steps) appeared around 1978 and were greeted with a spate of magazine articles using them, including voltage testers, and the ever-popular VU meter and spectrum analyzer projects (to go with your graphic equalizer project). "Those were the days..." Hahaha.
Last ones of those I got came from a company whose initials are BG. The chips that they sent did not have the two pins at one end of the package connected, and I had to source some elsewhere.
@@Roy_Tellason I'm confused. What two pins are you talking about? Did this render the chips useless? But then you sourced some replacement.... chips I assume, not pins, right? But if you did source replacements, then surely those were the "last ones you got", and not the ones from BG? I'm having difficulty figuring out what you are saying.
The kit that I ordered consisted of a small circuit board, a socket for the LM3915, stuff to support the chip, and 10 LEDs. When I built one the first two LEDs never lit up at all. Checking the rest of what they sent they all acted that way. Thankfully the part is still readily available, and when I got some other ones the board worked fine. They did make an adjustment to the money side of things..
You're close to understanding it. The LEDs in series does set up a stepped turn on point. They act as the reference voltage and the transistors are the comparators. The base (from the resistor network) has to get higher than the emitter (which is a series of LEDs) in order to turn them on. I think the extra diode is to add a bit of voltage for the "24V" turn-on point.
Yeah, you can use the forward drop of LEDs and other diodes as references, so long as they don't get warm...
But why not just adjust that turn on point with the 36k across the Zener?
I'm always interested and fascinated how circuits of the 60's-80's were designed that could do so much for how primitive the components were. Really interesting. It's amazing what people were able to do. You really had to think and consider every component choice. Today people have it easy with computer programs and AI that can help them design stuff and even simulate how components might interact with each other.
I remember my dad bought me a transistor radio kit made by Radioshack. So much fun to put together and learn how everything work together. Too bad the case was made of cardboard which got soaked in the leaky trunk of an old car and completely destroyed. Really miss that project.
That was a very nicely drawn schematic you did there, very impressive details and straight lines. and about the travel adapter safety, let´s face it, we all been a conductor at some point when working with electricity in one or another way :P
Had a few Steinel testers back when I started working in 92, were the basic led ones but had a button for continuity iirc. The wire used to fail from flexing and had a few near mises where nearly got zapped!
They were good because they wouldn't trip an rcd when testing live to ground, handy when working on farms during milking time as you become quite unpopular with the herdsman if all the lights go out and vacuum stops, cow poop and all the clusters fall off...
Some electrical engineers look at a transistor and see a switch. Some look at a transistor and see calculus. This was clearly designed by the latter sort.
Nope. It's a basic "emitter follower" which is useful for outputting at most input minus Vbe, but at B times higher current . There are 3 basic a analog modes in textbooks: Collector output with emitter grounded . Emitter follower and the weird "grounded base" circuit .
@@johndododoe1411- you left out the reverse biased variant and the collector and base joined variant…
@@Mark1024MAK Those are degenerate forms of the normal variant .
Great that you backwards engineered the workings of this electrical tester. It is a lot more complex than at first thought. We used the Bennings plunger duspol in the 70's till around the 2000's, and now the led or digital versions of the latter.
I remember similar schematic in early LED VU-meters and also FM tuner indicators in car radios. Operating principle is not that hard to draw but may be counterintuitive at first.
B32650 is the Siemens Part Number..
The secret of the transistors is quite simple: the voltage between base and emitter is around 0.6V, it is a diode. So the voltage of the bases is defined by the resistor divider and the emitter voltage is 0.6V lower. Because of the current amplification of the transistor the LEDs are fed from the collector. If you see the principle of the base-emitter-diode giving a 0.6V voltage drop the circuit gets much simpler to comprehend.
For reference, the design is called an Emitter Follower.
@@maraswen5614 I german native. Sorry I do not always have the right words on hand.
I just wondered if it's really the Siemens Halske Logo on there
I remember using something similar years ago in my first real job after college (generator manufacture) I'm 63 so I probably used one of the first. Nice to see these circuits. I love/hate microcontrollers (eyes not so good these days) but still a fan of discrete "seeable" electronics.
By way of encouragement -- if you're still playing with physical electronics as it's got smaller, consider getting a microscope. Both electronic ones and optical ones have their place. I love my rather aged stereo zoom Olympus SZ-something, not very expensive on ebay (sidenote -- 0.5X Barlow lens accessory is needed). Being able to see is important!
@@Graham_Wideman Thanks, I'll look into that. I currently have one of these magnifiers that you wear on your head and has interchangeable lenses that seem to work well enough for standard parts but smaller jobs are getting trickier. Perhaps I need to upgrade my patience too :-)
@@DonaldBarnett2014 I tried those magnifiers and found them better than nothing, but pretty unsatisfactory for surface mount. I had to use the highest magnification, and that requires very short distance to the work, and I don't like soldering that close to my face :-). Stereo microscope transforms the operation from struggle to pleasant! (Well, if you're into that sort of thing!) SMD soldering down to 0603 and 0.65mm pitch _by hand_ becomes surprisingly easy. And of course placing probes etc. If your hands have escaped any unsteadiness deterioration, then it's quite remarkable how finely we can work, if we can just see at that level of detail.
It seems clear that nothing much can happen until the 12V LED lights. Then, the transistor at the bottom of the LED chain can turn on, and so can the pseudo Darlington pair. The diode on the emitter of the first transistor in the chain appears to be there to keep that transistor (and therefore the rest) off until the voltage at the top of the 4.7V zener gets high enough.
After that it gets weird.
5:49 - My take on the BC556 darlington is that it provides power 'at low voltages' to assist in lighting the 12V LED and additional bias current for the constant current circuit formed by the BC546A and 270R resistor. As the voltage rises, so the emitter of the darlington will begin to level off at 39V, whilst the base will continue to rise, switching off the darlington. At this point, bias current and 12V LED drive will come through the string of resistors on the left. It is the BC546 which limits the current to the string of LED's (to around 2mA) and the PTC thermistor is there to reduce it's dissipation at higher voltages.
My guess on the 1N4148 diode is that, at 24V (input) the 24V led will be lit, but the 39V zener will not yet be conducting, therefore the circuit would be designed such that the base of theBC237 driving the 24V LED will be biased to conduct below 24v (16V according to your note). As the voltage rises to 39V, so the voltage on the string rises and the voltage on the 24V LED would be around 31-32V. This is likely to be above the base voltage of the driving transistor (the transistor is in reverse). I couldn't find good figures for the BC237B but my guess is either the reverse breakdown voltage or leakage current through the transistor affected the accuracy of the other transistors. Adding a series diode would remove this effect.
It would be worth reading the wiki article on 'emitter follower'
The output voltage follows the input voltage, i'm guessing the extra diode is to drop 0.6v before the led
I saw similar design approach somewhere else; note that the LEDs are connected in-Series (no pun!) to minimise load on the circuit under test. The transistor switches are configured to bypass the irrelevant LEDs - very clever
BigClive had pleasure in drawing this schematic :) I love that :) Thank you BigClive :)
I love these discrete circuits compared to microcontrollers. It's easy to slap an ubiquitous 8 pin microcontroller onto a circuit and be done with it (and often it's cheaper, quicker and takes up less space) but there's something cool about finding a circuit composed of discrete transistors and components.
Thanks for the education Clive, I really appreciate your effort to explain the circuitry. I think the capacitor provides a small load. You can use it to detect if "real " voltage is present or you can test a RCD with it. Single pole testers sometimes light up because of coupled voltage from parallel wires or similar. Since I found your channel I watch every video you put out. so much to learn :)
The curcuit is not mysterious at all. We used to make bar graph LED VU meters using exactly the same principle when I was a teenager (30-40 years ago).
The idea is very simple. Each transistor is an emiter follower. It starts conducting when the base voltage reaches the forward voltage of its emitter LED plus the base-emitter offset. The resistor divider ladder feeding the bases determines when that happens.
The darlington pair plus the bottom transistor form a current limiter. As the current through the LEDs rises, so does the voltage drop between the positive rail and the darlington emitter. But the voltage at its base does not, it is only determined by the input voltage. Thus, the darlington base-emitter voltage difference drops and the darlington closes, closing the bottom transistor (the one with all the LEDs in its collector) and reduces the current through the 12V LED.
Other components, like the diode and the zenner, cater for non-linearity of the indicator.
I just took apart an electric stapler that finally died. 1999 was printed on the pcb. I was surprised by its complexity and the tiny but powerful motor in it. It couldn’t run mechanically but all the electronics still work. Pretty cool
"It's hard to follow because it is devious and clever". High praise indeed! Its like Lock Picking Lawyer saying "I would buy this lock"
Love seeing the old Siemens & Halske logo on the cap
Thanks for this interesting old circuit.
Old school high cleverness level right there :) As you said it takes some time to wrap around so much analog things happening at the same time, not obvious at all, and it's not easy to divide the circuits in parts
0:30 Note the black stains on the "deathdaptor" - scars of some previous battle, no doubt.
Great to see the return of the deathdapter, with its sooty skidmarks
That was just ONE crappy USB charger that exploded as soon as I plugged it in, before I even had a chance to make a video about it.
@@BigClive I was worried the skidmarks might be conductive, but you will have thought of that.
NOW I know what to build with all my old components.
The weird thing about this circuit is that the BC546 is both a current source and a switch. The other transistors are in emitter follower configuration so just buffering the voltage on the resistor network. The 4.7v zener and the other diode in series with the last transistor emitter should be there to make sure the 24v LED lights up above 16V: 12+4.7-0.7 = 16. Something like that.
A humble suggestion Clive. I don't think it helps to see these transistors (the BC 327's) as digital switches. They are, of course, emitter followers. The pnp darlington in conjuction with the BC546 is a sort of current mirror (or compensator) so that, as the voltage increases, the LEDs each maintain the same brightness (fixed current). The "jack-up" diode on the lower BC327 just provides the correct bias (regarding the presence of the 4v7 zener; 4v7 have almost 0 tempco). The "12v" LED makes an excellent regulator if its current doesn't vary too much.
This doesn't seem too odd to me (now I'm showing my age, started electronics as a hobby in the late '60's, worked in the industry in the late '70's) as often we would have to devise things around transistor characteristics (though I've forgotten Ebers-Moll). A friend and I needed to make a very low noise regulator (for a RIAA pre-amp; BEO cartridge if I remember) and we decided to use LEDs because zeners can be very noisy.
Anyway, thank you for this interesting circuit, an interesting "blast from the past".
Can we all just stop for a moment and appreciate the sooty scorch marks on the death-dapter?
NEARLY 1million LETS GO BEEN HERE SINCE 20k
I've been comparing the datasheets for the BC237B transistors used for the LED drivers and they're almost the same as a BC546B. About the only difference seems to be the E to B breakdown voltage, which is 6 volts, compared to 5volts for most others. I'm trying to figure out why they chose the BC237B for the LED drivers.
Yeah, it's strange they used two different types.
Usually cost related when you see a variety of parts where one or more would perform fine in all positions. It's my understanding that with transistors they were once so bad at making them only a handful would make the high military grade or whatever, and then the progressively crappier ones would be picked out, marked, and priced accordingly. All the way down to unlabeled parts that "worked" but didn't make the loosest specifications, these were sold to hobbyists. Old transistor catalogs gave clues of what was what by giving you process numbers for everything.
Well the BC548 is a improved BC108 in a plastic package, the BC546 is part of the same family of transistors in a plastic package.
The BC237 (which is a BC107 in a plastic package) is older than the 500mW rated BC546. Depending on which manufacturer of the transistors was used, the BC237 is either rated 300mW or 500mW. In any case, the reason for the different types is likely cost, one being slightly cheaper than the other.
Note that the suffix ’B’ is the gain grouping.
It reminds me of an old LED VU metre kit from the Australian Talking Electronics magazine of the 1980s.
Aye thats headache inducing. From what I can see its the darlington pair thats setting the voltage on the right hand side (the zener simply caps it at 39V). The emitter will be 2vbe above the base voltage which comes from the point between the 270k resistor and the ladder on the left. The bottom transistor is acting as a constant current source for the LED string.
I think that darlington pair is ensuring that there is sufficient current to light that 12 V led and make sure that the current source transistor has enough voltage on its base. I can't see the darlington being used to to set the voltage on the right, as it's pulling down, not up, and it's not pulling to the 0v rail, rather the base of the current source transistor
That Death-Adaptor has some suspicious black marks on it........ LOOOOOOOOOOOOOL .>>> LOVE IT
I remember once seeing a simple Neon based circuit, using exactly the same theory.
Only difference is that the little glass neon indicator lamps turn on at about 55volts. So the transistors were rated higher.
You can use a decatron tube (if you can find one!) as a really cool bargraph indicator.
Looks like a Common Collector design similar to what some older linear DC power supplies use to get high current (10 amps +) output through power transistors, usually something like a 3055's in a TO-3 package. There is a Common Emitter design also which is the more standard way since it switches the low rail (negative).
The cheap Chinese versions use a bootleg LM39XX IC in SMD form that had it's markings laser etched off or an SOC blob that does all the display stuff with dodgey isolation of course
I remember making a couple sets of test lights as a teen, this was about 10 years ago. I kinda just cheated and used the potential dividers to drive the lights directly, I had a low-voltage DC test lamp made out of LEDs (a cascade of color using the forward voltage as a reference, started with red LEDs up to 5 volts, then a blue one, then back to red for granularity up to 14, then blues up to 24V) and then a high voltage AC/DC one with neon indicators that went up to 600V iirc, for messing with vacuum tube gear. This is a little more elegant, has some actual safety in the design and means you don't need 2 sets for different ranges, but god the granularity of the red LEDs on low voltage was extremely useful even if I did have to hold my hand over the thing to see the topmost LEDs...
OMG
I recognised that circuit board as Steinals as soon as I saw it in the youtube 'info/ link' picture grab.
These and the Steinal combi checks were my go-to testers in the 90's They went with me EVERYWHERE including quite a few places I'd rather not have gone myself! Like the macerator pits lol
Nothing a bit of morgue strength disinfectant from ' up above' wouldn't fix tho.
Always dependable and reliable quality not like the Chinese crap we get today.
They were ahead of their time.
They all did eventually die
After decades of service
I should dig them out again, now I've got time and restore them to their former glory
With any luck the disinfectant smell may have eased off a bit by now , as that smell stuck to everything lol
Well done Clive , on yet another great
Teardown
Along with a great blast from the past
Keep up the fantastic work !
Are those carbon composite resistors i see? Definitely a blast from the past!
The transistor on the bottom right is a constant current sink for the LED chain. The current through the 270Ω resistor will be held at about 3.7mA (controlled by 1.8V (12V LED drop) minus 0.7V B-E diode drop, the difference over 270Ω).
The divider chain and transistors is pretty straight-forward .
Not sure if they're film or composite. I'd guess film.
@@BigClive Most are film, but the ones with dark brown bodies and square ends look like carbon resistors.
7:00 the 1N408 diode seems to be for Emitter-base reverse breakdown of the adjacent transistor
excellent you analisis,made a diffficult circuit seems so easy ! regards from mexico
I'm thinking that the extra diode is to drop a known voltage across the LED for 24 V since it's otherwise redundant. They must have been having trouble with either the LED not turning on decisively or being over voltage when it was the only LED being lit.
I agree, a very strange circuit. I think they started with a resistor network to drive the NPN transistors to turn on the LEDs (because: old school relay signalling design) and the basic current limiting PS (resistor and thermister and zener) and everything else is there to solve one problem or another on the bread boarded prototype (caused by low impedance relay design being applied to a high impedance solid state design. When you look at it this way it seems to make more sense.)
I built an LED test light in the 1970s, still have it. It only has 1 LED but works from low voltage to mains. It also has a button for continuity testing. At this point I don't remember what the circuit is.
I forgot to mention, the LED on mine is always the same brightness. I'll have to dig that out and figure out what I did.
Possibly a two transistor current regulator and backup resistor?
@@BigClive probably, wouldn't have been any more complicated considering the year.
Thank you. Keep working, good luck.
12v led and Bc56r is current source for 24 -400v leds .Divider chain is buffered by emitter followers
630VDC is fairly common for "mustard" capacitors; these tend to be rated 250VAC. 650VDC/470VAC is also somewhat common for X2.
Did you test this with a DC or AC supply? If DC, the difference you're seeing might be RMS vs peak.
These test lights are indeed standard in the electrical industry. I work for a Dutch DNO, and we must prove dead with something very similar. One advantage I haven't seen mentioned yet is the way you hold the probes means your hands stay relatively far away from the (typically) fully exposed rails carrying 230/400 V. Remember that there's no safety equipment, like RCDs, in final distribution substations.
Ooh. It looks like that adapter has seen some action. 🙂
Mainly one piece of action, but it was particularly violent and I was holding it at the time.
@@BigClive Wow!
Can't make heads or tails of that circuit aside from exploiting the stacked voltage drops across the LED's and bases to indicate voltage. I guess the diode at the emitter of the lowest transistor is to slightly increase the turn-on voltage of the 24V indicator. The lower Zener might have been used for that 12 to 16V gap and the upper Zener is just for over voltage protection.
I remember my parents at the carnival buying me a plastic cap with LED's that ran on a 9v battery, those LED's look the same... :)
Very interesting indeed!
Worth taking apart!
I wonder if the 12V LED at the bottom left of the schematics doubles up as a quazi Zener to set up a stable current to the base of the main transistor?
It apparently does .
As someone else pointed out, the bottom right hand transistor is a constant current sink to make sure the current through the LED string is the same regardless of the number of LEDs lit. Its base will be 0.6V above its emitter, so if its base is held at constant voltage then its emitter will be as well, and as that feeds a resistor, Ohm's Law dictates that the current through that resistor, and hence (approx) through the LEDs, will be constant too. The voltage between collector and emitter will vary to keep the current constant.
The logo of the capacitor up top is of "Siemens & Halske" which went defunct in 1966, when it was integrated into the Siemens AG.
Though, I'm no sure if and how long they continued to use the logo after '66.
Either way... it's historic. Thanks for sharing.
That logo appeared on railway components at least untill the late 70s and early 80s. AFAIK the skipped the Halske name at some point and reinterpreted the sign as a motor similar to the Bosch logo.
That big capacitor is 500V rated, old W.Germany Siemens factory sometimes didn't print the "V" letter._
"I'll defeat all the safeties with this deathdapter"
*pulls out charred adapter*
I love how bizarre some vintage circuits can be.
It's so dependent on the specs of those transistors, if you sub anything you'll have to go thru and redo all the resistor values too. Yeah I'm glad I didn't have to design that!
Common collector circuits follow voltage (minus the B-E junction drop) and amplify current.
The yellow capacitor has a Siemens & Halske logo on it.
congrats on the 1million subs
That deathdapter has seen the magic smoke…
If it's a grey case, I got one of these. Triggers the RCD If you probe between Earth and live.
the numbering starting "B" on the 36nf cap looks like the old mullard/Philips 12nc systems and others so it is telling you construction and series rather than capacitance if you have the key
Very interesting. Thanks for sharing.
many, many, many years ago I had a martindale tester that vibrated which was fun🙂
I have one in a drawer.
@@tbelding I think a girl friend took mine🙂 can't think why she did😃
Great find and you could actually build one of these yourselves people too! Wonderful
Love the smoke stains on the deathdapter!
They were as loud as they look. Sadly the camera wasn't running at the time.
any time you see a 1 watt+ resistor it is an old design, last time i saw that big a wirewound that wasnt in a cemented cube it was being used to drive a helium neon tube!
Siemens capacitor and ITT diodes? Nice!
It feels like this is a distant cousin to a ladder DAC
I've got a set of these , they're no name, IP65 rated and the circuit board must be tiny, fits in a 12mm tube, I'd be happy to send them for analysis.
B32650 is the Siemens Series Type Number for that MKP capacitor. That type is obsolete.
It's a very old tester.
I would like to see you bread board it out and definitively suss out its workings. Please.
What will the 1m subs special be? Presumably only a few weeks away.
Probably longer than that. I'm trying to think of something worthy.
Beautiful, it was made in a time in that even a simple device like it had just quality parts, no Chinese garbage like nowadays. Maybe I saying something stupid, but I see it like a kind of a voltage comparator array or a LED VU meter...
Very similar to old VU meter circuits.
Seeing this makes me want to crack open this old line polarity tester that has neon bulbs, I think? Doesn't have any manufacturer info on it, so I'll have to go digging.
I've covered a neon based voltage tester in a past video.
@bigclivedotcom I searched through your past voltage tester videos and couldn't find one quite like this. After some digging around, it turns out to be an AUL instruments model 1410. It was designed for the US military in the late 60s, though I can't tell when mine was manufactured. I imagine the circuit to be fairly similar to the one in this video, just with the lamps for reliability or repairability, perhaps. I'll have to get a chance to bust out my old tools from storage to take a gander inside. Your videos always make me wanna get my hands back in some gear.
Cheers
I had two pairs of test lamps once, one for 12v DC for use in car and motorcycle repairs and one for up to 400v mains voltage. One day I was fault checking a mains voltage device and grabbed the test lights which were both lying next top each other and started preobing. Suddenly I heard a rather loud bang and the magic smoke escaped, turns out I grabbed the 12v ones and poked into a mains connection.
Please keep your tools seperate from each other and double check before probing into things, otherwise the results can be quite startling.
I have now been working for a well known yellow cased multimeter manufacturer for some time where their version of this is produced. I can't help but wonder if it has similar circuitry.
I still use a Square D neon voltage tester but its not cat 3 certified.
Does anyone remember the "Digiscope" LED oscilloscope project in Practical Electronics in 1975?
It’s funny I always thought it was NE-2’s with a voltage divider (or several separate dividers) across the mains.
Some do use neons.
It' looks like they are using diode steering using the junction inside the transistor
Damn...yeah that would take a minute :)
Who's like me remember the famous UAA180.
Definitely looking a little bit agricultural ☺
i picked uo a steinel 'combi check' thingy(leds and a continuity beeper) for a pound or so from a car boot sale unfortunatley had been wet inside, bit rusty, i cleaned it out but still didnt work right, after resoldering pretty much everything, now seems 'correct'..,
now picked a small steinel hot melt glue gun, its 'element' seems to be a combined ptc AND ntc , as it measures very high resistance when cold, i thought it was dead! but doing resistance checks every 30 secs or so (unplugging first, of course, before each test!), shows resistance first reduces as it warms , gets to a point, then increases until fully warmed, its rated for 100 to 240v mains so i suppose this is 'necessary' for it to work over that wide voltage range with no adjustment/switching ,