Sometimes simpler is better — when you don’t need the the computational power of an onboard microcontroller, it’s often best to rely on a simple circuit to get the job done. With cheap Raspberry Pis and ESP32s all over the place, it can be easy to forget that many simpler projects can be completed without a single line of code (and with the ongoing chip shortage, it may be more important now than ever to remember that).
[mircemk] had the right idea when he built his simple induction-balance metal detector. It uses a couple of 555 timers, transistors, and passives to sense the presence of metallic objects via a coil of wire. He was able to detect a coin up to 15 cm away, and larger objects at 60cm — not bad for a pile of components you probably have in your bench’s spare parts drawer right now! The detector selectivity can be tuned by a couple of potentiometers, and in true metal detector fashion, it has a buzzer to loudly blare at you once it’s found something (along with a LED, in case the buzzer gets too annoying).
All in all, this metal detector looks like a terribly fun project — one perfectly suited to beginners and more seasoned hackers alike. It serves as a great reminder that not every project needs WiFi or an OLED display to be useful, but don’t let that stop you from overdoing things! If touchscreens are more your speed, [mircemk] has got you covered with a smartphone-integrated version as well.
Just looked at this project for the second time and was thinking a pot for volume would be nice. Going to construct it to see how well it works for me.
I don’t happen to have a dual timer on hand as far as I can say, but it seems a 556 would work and reduce component count by 1 unless there is an issue with having both timers so close.
I remember back at school in the 1980s making a metal detector with a single transistor and a handful of passives. Worked well enough to find coins dropped in long grass. Obviously modern metal detectors are all about detecting specific types of metal and being able to exclude stuff like rust, but it does show that you can get something useable for very little.
Be sure to check local laws first. In Poland metal detectors are treated the same as firearms and must be registered with Police. To perform metal detecting you must first obtain permission from local dept. of archeology, present plan for archeological research, what you’re looking for etc.
It was fine until around 2009 but then law was greatly tightened to conform with EU standards.
Doubt EU has anything to do with it, as other EU countries are nowhere near as anal about metal detecting as poland is.
This looks pretty neat. Hopefully the “modification to support two 555 instead of 556” as mentioned in the article isn’t too specific to having separate ICs, since I might have 2x 555 but I definitely have a 556 (from Radio Shack store closing clearance). Think all I might need to get is the potentiometers.
A 556 is two 555s end to end.
I wonder if that’s due to the fact you can easily use a metal detector to find buried firearms. I mean, there was a bit of fighting back in Poland in the 1940s that might have cause a lot of guns to be buried in haste, and some of those guns might be in caches or the like and such will be in good shape.
Or UEO!
UXB or ERW to the rest of the world – UnExploded Ordinance , UneXploded Bomb, Explosive Remnants of War.
Make sure to look up local regulations before using metal detectors.
Poland: (Ustawa z dnia 23 lipca 2003 r. o ochronie zabytków i opiece nad zabytkami (Dz. U. 2003 Nr 162 poz. 1568) defines metal detector usage a felony, 2018 amendment makes it a crime.
https://histmag.org/Wykrywacz-metali-nowe-prawo-w-Polsce-a-poszukiwania-zabytkow-16283
You can report archeological find, and there is even a reward, but only if you found it accidentally without intent. For example farmer dragging stuff up with a plow, or builder digging a well. Reporting a find with metal detector is a crime with up to ~$100K and 2 year prison sentence, or up to 8 years if experts deem you destroyed something by accident.
https://www.adwokat-prawo.com/post/nie-legalne-hobby-poszukiwanie-zabytk%C3%B3w-wykrywaczem-metali-w-polskim-systemie-prawnym
I wonder how a few magnetometers would fair with a coil to chirp out a signal, so it acts a bit like poor man’s ground penetrating radar. Some of those magnetometer based metal detectors are prohibitively expensive but manage to go down several meters with ferrous metals. It seems that they should be able to see nonmagnetic materials too if radio waves were induced into them and then rate of change and angular phase were also measured rather than just signal strength. Having a head with say eight compass sensors and then subtracting them from each other could make for an interesting tool. Perhaps it could create a virtual map if positioning could be accurate enough. Utilizing something akin to 123DD like 3D object scanning, to stitch sections together.
Carl & Jerry in Popular Electronics in the early sixties built a magnetometer with a plastic bottle full of water, wound with a coil, and an osciiloscope for display.
They had big hopes of finding buried treasure, they used it on a farm, only to find junk.
It was fiction, but the stories were based on fact. So maybe an article in Scientific American (The Amateur Scientist) covered the idea. Probably easier now with tablets tyat can be oscilloscopes.
IIRC Practical Electronics in the uk had a similar article in the late 60s/early 70s featuring two plastic washing up detergent bottles and a 5ft broom handle. Probably some germanium transistors too.
I’ve always been of the opinion Jerry’s been wasting his electronic design talents since he left Carl for Ben.
What?
No mention of the Revenge of the Nerds movie where they were left on a deserted island and built a metal detector from coconut shells and a transistor they made from sand?