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- Опубликовано: 19 июн 2024
- How does a metal detector work?
Dave teardown and reverse engineers the circuit in a $17 Harbour Freight wand type metal detector, and also explains how to do basic reverse engineering of a PCB.
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Наука
I see you turned on the grid lines on the Dave CAD program
klarusboy
Cant afford the parallel processing expansion tho.
Where can I buy this awesome piece of software?
BaNenKy Australia. No shipping.
Always learn a lot from these. Thank you!
Dave's latest videos have been kicking ass.
I really appreciate these "Reverse Engineering" type o' videos. Very good work! :-) Thank you!
Dave, thank you for inspiring me to get back into electronics and digital technology.
You've upgraded DaveCAD!
Yeah, this probably is the registered professional version without the DaveCAD logo . .
Good video. I like getting back to the basics. Please, do more videos where you discuss circuit operation at the nuts and bolts level.
Listen with headphones to unlock the tinnitus achievement.
Good job as always. Thumbs up.
I'd love to see a tear down of one of those expensive metal detectors. Got any treasure hunting mates Dave?
Great video, thankyou.
Dave cad is excellent tool, yellow background is easier to see. Good video thanks.
I built one from plans a long time ago that used one transistor and a pocket AM radio. It was a BFO, I think it relied on beating with the LO (local oscillator) in the AM radio, as both the tuning capacitor in the circuit and in the AM radio changed frequency. It counted on poor shielding in the radio, which of course 7 transistor pocket radios weren't exactly well-shielded.
I've seen other designs that use a 455kHz IF transformer as part of the beat oscillator, and couple both signals into an AM radio, using the IF section.
that was really great dave! do you know what could make the range of the coil go further? maybe a bigger coil?
I really like my pin pointer. It works perfectly well and its real bargain. Great for locating things my woodshop vacuum has accidently devoured. Love seeing it reverse engineered. I really admire what engineers who are up against wall can coax out of almost nothing. Thanks!
Thanks for that!
That's what I use for detecting. The pushbutton switch is garbage. I put 2 vibrators in and 86'd the beeper.
Would love to see other improvement mods for use as pinpointer for digging targets.
Thanks! I think I mostly got it. Still a little unsure about how the oscillation works starts/works or why it stops with metal but that's a different topic. I think I followed the rest just about
Well explained.
EEVblog Thanks Dave, very interesting. I would enjoy seeing this mocked up and of course the next logical step... how would you improve it. Would the improvements increase cost or perhaps even reduce cost? I think this would be very beneficial to many.
The buzzer's function is here implemented similar to an Idiot Light on a dashboard. A possible improvement (to take advantage of the human pattern recognition capability) my be to instead send a variable output signal to an audio speaker. Along those lines, perhaps the dual comparator part you mentioned is just what remains after the maker adapted the circuit from another more sophisticated model?
I think just the fact that they can get all the parts for this (including the plastic molded cases), have it assembled, SHIPPED, put on store shelves, sell for $17, and STILL make a profit is crazy...and it works, too!
Dave, a slightly different way of interpreting this circuit is as a Hartley (transformer-coupled) oscillator where the amount of feedback and the Q of the tank circuit are changed by the presence of a conductive material nearby, which then changes the operating point of the oscillator (the extent to which the total loop gain exceeds 1, pre-distortion, varies, which then requires a different amount of distortion to achieve a constant amplitude, stable oscillation, which in turn changes the DC operating point of the oscillator). This change in DC operating point is then amplified by the transistor with the filtered output and this is fed to the comparator.
Yes, we can see the DC changes at the bases of Q1 and Q2 at 18:04 and even better at 18:34. The capacitor at the collector of Q2 is actually a cheap linear average stage which cancels out(shorts) the ac value.
Sean Breheny I didn't quite see it as a Harley. But yes, it's certainly changing the DC operating point.
Usually Hartley osc. have two coils in series or tapped one (also tapped with transformer).
The portion of the feedback signal is taken from the inductive divider.
Colpitts osc. --> capacitive divider.
And I think a Harley osc. would be some of the coolest thing I ever seen in my life...power,noise,smoke,adjustable frequency over a wide range,easy to refill...
Dave, what`s about the Indiana Jones HO scale model train set, does Sagan not make pressure on you?
Hey I love this pin pointer, I added a vibrator function, When pin pointing something in a hole It lets me know right away, Plus the noise but it will pick up anything, I have used real good ones and this one, There is no difference. Works great sad they don't sell them anymore.
Thanks. Going to buy the Orange GP then. Going to try looking for gold during the summer here in WA. Hard to do classes during summer. Nice reverse Engineering. I thought it was something like that. Have you seen the Electric Cabin Scooters on Ali Baba for $1500 - $3000 ? I heard some are headed for Europe in the North. Was wondering about batteries and charging plug Standards differences.
I add the part numbers onto the R.E. schematic to track what I have used and what not.
Dave, upon hearing the phrase "half a bee's dick", i have officially soiled my desk with my morning coffee.
EEVblog - Hey dave, where do you get the grid paper you're using in this video? It looks really nice, better than the exercise books etc I've been able to find to use for schematic drawing. Cheers!
I have a question! Can I use wire that's insulated to make coils? Or does bare copper work better? For instance my 100 foot extension cord plug broke so I tore it apart to use for electronics. (I have more) and plan to recycle the casing into parts for my build...
Well it does work. Not bad really for the money. Cheers Dave.
This video give encouragement for people who want to get involved with electronics. With little expense and a quick Google, You will soon have a B.F.O detector up and running.
Big Thumb Up.
Hey Dave, you mentioned simulating the Circuit. I'm searching for a good Simulating Software für Beginners. At the time i'm stuck with this Software PICAXE-VSM (just google ;-) i dont want to be accused to do ad's) it's quite cool, but i wonder if there is something better?
It uses pnp fet at out put whn comparator goes off the buzzer will ring. This is why if the oscillation is broken it does not affect buzzer perfomance.
Hello Dave!
where some say crude others say elegant! for 17 bucks its pulls its own~!
I actually own one of these detectors. I use it to locate nails in reclaimed wood before cutting with the power saw. It does the job nicely if you're careful and don't go too fast.
You get what you pay for though.
"tweaking by half a bee's dick" absolutely sent me, I love it and am adding it to my repertoire!
Playing it safe *puts on glasses*
YEAAAAAAHHHH
Could you please show the coil length and type of wire?
What is inside the wand, I mean.
Thanks for blowing up my ears with that beep
I just bought a proper MD.
But I'm interested in possibly designing/making my own for academics.
Would a DSP be useful in a MD?
Thinking of a 'hello world' project for learning DSP.
(Al Loom in um :P)
cool i have the same one now i can see how it works.
nice seeing how a metal detector works.
And if ya don't mind a question do you need TVS on a H-Bridge circuit for stepper motors. Fried a small breadboard for 97 Electronics Now Feb, "Build The PC Drill", James J. Barbarello. He didn't have any TVS Diodes in the circuit. Went throught it 2x w/ highlighters. It locked up strong but when I shut it off it smoked. LOL!
I love the DaveCAD, where can I purchase one? :)
Dave you should do a 20sec tear-down of the "Rangertell" metal detector,a true low tech super priced solution,hand me that calculator.
Can you see Dave in 11:22 ? (Between pins 6 and 7 of ampop) :)
I have a CEN-TECH Multimeter, does the job. I just have to replace the leads every now and then.
Good for cable detection in the wall ?.
I fix a lot of expensive equipment, and all I see is bodges, and lazy people using plug and play modules. The cheap dime-a-dozen electronics have the real design work put into them.
This thing works great as a cheap pinpointer. I modded mine with a cell phone vibrator motor in place of the buzzer. Eventually I'll break down and get the Garrett, but for $15 I can't complain.
Often used to detect nails, etc., in trees and finished lumber. A spike in a tree can injure or kill a logger. Metal in finished lumber can damage woodworking tools, planers, etc..
Perfect timing. I'm tearing my hair out at the moment trying to design a simple inductive proximity sensor. I'm feeding a square wave into a tank circuit, half wave rectifying the sine wave output of the tank circuit, then feeding this level into an op amp configured as a comparator so that the presence of a metal object near the coil affects the resonance and amplitude of the sine wave from the tank circuit. The coil I'm using is a 470uH inductor with a ferrite core straight off the shelf from my supplier. Problem is that the detection range is very small and there appears to be a lot of drift in tolerance (might be the breadboard?)
The diameter of the coil is the largest determinant in sensitivity. A ferrite choke won't get you much sensitivity. Larger coil diameter equals better sensitivity. Depending upon your use, it may pay to wind your own.
Just had a look at Harbor Freight's site and this model is currently priced at $17USD. They also offer a $40USD model and looking at customer reviews...
"Fantastic product that works perfectly for security purposes. Extremely value for money."
Hmm?
That's a pretty nutty design. I have no idea why they made it that complex and expensive, a thermistor, seriously? The set point compensation seems mostly pointless when you have a sensitivity adjustment. Hardly seems like it was designed for continuous use, no real effort was made to reduce current consumption, except maybe using a TL062 which is < 500 uA, the oscillator and crappy regulator would eat more. Dunno why they bothered to use a JFET amp at all, or not use half of it for something less primitive of a bias servo. The buzzer looks like one of those electromechanical disk ones rather than a piezo, it is cheap no doubt, but likely so inefficient they needed to use the MOSFET switch instead of just picking an op-amp with enough current sink capability. The design needed a multi-turn precision trimmer which is an expensive item and required manual calibration during manufacture which seems dumb. Looks like they used a nice cap for the tank, not sure if that is cargo cult design or if someone actually knew what they were doing.
vk2zay They used a JFET amp because that would have been their go-to amp and they likely had a zillion in stock, rather than any technical reason.
I wonder if it cam be used as a pin pointer in metal detecting
have you ever dismantled the water detector locator, if not yet I want you to disassemble the water detection
Is there a reason why this video isn't listed yet?
I just went to a Dave Jones EE College course! Awesome!
The safety rules - i know the last washing powder i bought, had a warning on it " use safety gear when handling the product".
Metal detector reminds me of those old timers at the beach, they look so weird scanning the floor.
Informative lecture even if the product was el-cheapo. I wouldn't mind seeing a lecture on a more expensive detector (does anyone have something to donate to Mr. Jones?)
I actually really like Harbor Freight for some things. A lot of the time its just rebranded Matco stuff. That being said though, you need to be careful what you buy there. Most of my hand tools are from there because they tend to be ok quality.
I've bought power tools from there for stuff that I only plan to use a few times, compared with buying an expensive brand name tool. I've had some good luck with their "Chicago Electric Brand". I agree the hand tools have been fairly reliable. Definitely not the tools for hard use and abuse.
Oh, I think I get it. It is intended to be a "marginal oscillator" design, the thermistor is probably ALC to keep it from saturating hard - to make it more sensitive. I'm not sure that's the best topology in that case, I'd be tempted to build an ALC loop around the extra op-amp and control a current source in the tail of a differential oscillator then sense the control voltage.
the thermistor is to stop temperature drift, something this design suffers from, there are two versions, one does not have the ntc, buzzer and other bits, but the board is prepped just not populated adding in the missing parts upto the higher spec makes the pinpointer run better.
"Tweaking by half a bee's dick" hahahaha, love it!
Any chance of an Advantest R6142 teardown being in the pipeline?
***** Ah, thought I'd done that...
I would like to see you simulate it.
Harbor Freight puts this ANSI sticker literally on everything. You can buy a set of pencils that recommends wearing ANSI approved gloves :)
The design is actually not bad at all!
In NZ we say Alu-Min-E-Um although with our NZ accent it's more like Alla-Min-Yim. I've never heard anyone but someone from the US (or a US tv show) call it A-Loo-Min-Um
How does the tank circuit work exactly? Where is the negative feedback?
+Aerohk: "Where is the negative feedback?" Actually you must have positive feedback to sustain oscillations, this is obtained with the polarity of the transformer's windings.
More videos like this please
just wondering if a satalite finder could be hacked into a gold or metal detector
Hi. How deep can this device go underground?
Most stainless is non-ferrus ;)
Ferrous means that it contains or is made up of iron, so how isn't stainless steel ferrous?
"Important non-ferrous metals include aluminium, copper, lead, nickel, tin, titanium and zinc, and alloys such as brass. Precious metals such as gold, silver and platinum and exotic or rare metals such as cobalt, mercury, tungsten, beryllium, bismuth, cerium, cadmium, niobium, indium, gallium, germanium, lithium, selenium, tantalum, tellurium, vanadium, and zirconium are also non-ferrous. They are usually obtained through minerals such as sulfides, carbonates, and silicates. Non-ferrous metals are usually refined through electrolysis"
You can't make steel without iron. /facepalm
Steel by definition is largely iron. Almost always >90% iron in practice. Ferrous = contains iron.
I think he just meant non-magnetic (at least, one hopes that's what he meant). Austenitic stainless alloys tend to not be magnetic, while the ferritic ones are.
Hi man
Can you help me? ?????
To strengthen the circuit??????
I'm 5 years late, but I'm here to tell you that I'm disappointed that you didn't notice the strengths of the MPSA18. Minimum beta of 500 for collector currents above 100 uA, with typical figures around 1000. ft of at least 100 MHz, so plenty of speed for low frequency AM.
this video is great! and these types of videos are awesome for beginners like myself!
edit*, the "half a bees dick" comment had me dying!
Another mystery unraveled... I have one and need to add a pot or something to quiet it down at times to stealth mode. Whenever I try to use it in the yard, to find a screw or something I dropped, the neighbor's dog starts howling. Or, connect the circuit directly to the dog and do away with the beeper. Arrooo... there it is.
Thumbs up for the Kookaburra :)
This old lady knows her shit!
Its pin pointer?
neat
YES!!! Reverse Engineering!!!!!!!!!!!!!!!!!! and hes going to hook it up to the scope! SQEEEEEEEE
DAVE do a video on eddy currents!
_"Hi, this is a bit of a ketchup video..."_
And here's me thinking it was a Mustard or Pickle video... :P
And now i find you HERE.... :)
Youre everywhere.
Is that gold coin a kangarand?
Aargh! Beeping like that seems to come across a recording with much more apparent loudness than other sounds!
I had to stop around 2 min Dave, I couldn't tolerate the beeping. Man I'm getting old. :/
Definitely get what you pay for. :-)
Inches??? Come on Dave, you are not that old!
DaveCAD 2.0
Pretty good job for 17. Dollars I have 200 dollars one that what u need when metal detecting to pinpoint on the ground
Create some circuits! Browse for androidcircuitsolver on google
13:42 -- Half a bee's dick!?!" Aus Tral Ya! Aus Trail Ya! :)
Really?
please build one from scratch! :P
You can call me Al. Americans saying sodder really hurts, aloominum is not so bad.
+mart fart said: " Americans saying sodder really hurts." FYI in American dictionaries it shows the "L" as being silent, for about only for the last 50+ years.
I love it ........... thx Mr.Dave
I am Mouhamad A.H. from Lebanon a 1 of your fan :)
Bob is not my uncle!
I own a $1200 professional metal detector, and it runs on a 9V battery. Metal detectors don't draw very much current.
s like a darkington pair
Question is, can you make this product cheaper? Smaller? Better?
parts + grid pcb, below 5$.. maybe even below 2$
You reckon somewhere in this world, possibly a developing country there is probably an entire building of the cheapest most unskilled labourers sitting there putting these together one by one in a massive assembly chain, and the poor guy who has to put that glue on is half asleep with sheer boredom.