Need help - Matchless Metal Detector

[WM6]

Thanks Davor.

Sure, there are much better MD solutions, but if one want to check something simple, as for start in MD DIY, this is good and from author outstanding well explained/documented project.

[Davor]

It is not theory, just nonlinearity. Crystal headphones of the olden days of radio were made with a more solid piece of piezo salt crystal that was mechanically coupled with a membrane. Linearity-wise that contraption sucked big time, but also provided some level of demodulation. So when you look at some ancient schematic and see some of these, you'll be in trouble explaining WHY that particular thing works at all.
Nowadays piezo's are much better sound sources, yet their equivalent in electronic sense is - a capacitor of a few hundred nF. They lack the most of the nonlinearities that made the olden headphones work their magic. Some nonlinearities must be present so I guess that might work - as worse piezo as better sound
So far I was not inclined to make a circuit that would mimic the behaviour of the olden headphones, mostly because I don't have any to compare the results with. You could try connecting a capacitor of ~100nF in series with a combination of diode and a 2k resistor to gnd i.e. a simple detector. Some amplification and you have a sort of crystal headphones equivalent. I have no inclination of doing it myself because of the vast choice of better solutions.

[WM6]

I am trying with two different CMOS version (do not remember which brand any-more) and both worked, but no one as author promise.

In soil very shallow depth of 4-5cm or so max on bigger coin.

Davor, you do not need "incredibly rare headphones". Cheap and widely available piezo element will work very well:

BTW, how "demodulation happens in headphones", can you explain theory behind this?

[Davor]

hmm...this mean I cannot use a standard headphone? like standard/common mp3 player headphone?

Nope. In this particular device demodulation happens in headphones, so in case you have some incredibly rare headphones as per specification - it will work. Otherwise you must demodulate the signal first, say with a diode, give it some boost, say using a LM386 amp, and supply it to mp3 headphones. Do you have an oscilloscope?

[adiputra]

Try any of the CMOS 555 variants (7555), most will work - although the detector won't!

hmm...you says " although the detector won't" - what do you mean by that?

[adiputra]

Hi adiputra
cmoc variants ICM7556IPD,TS556CN,,
TTL variants NE556,LM556,UA556PC,,
-According to her job if the timming has to be cmos, if job is sound use any.
best time
j.

ok, so in this project can I use NE556 IC? or others like as you said LM556, UA556PC? if I use one of this IC, the circuit still working right?

[adiputra]

556 is double 555. Ask for CMOS variant of 555, everyone will work. The most critical in this build are the headphones. Replacing them with something more common will be a challenge. You could replace them with some simple detector and amplifier.

hmm...this mean I cannot use a standard headphone? like standard/common mp3 player headphone?

[jap]

Hi adiputra
cmoc variants ICM7556IPD,TS556CN,,
TTL variants NE556,LM556,UA556PC,,
-According to her job if the timming has to be cmos, if job is sound use any.
best time
j.

[Davor]

556 is double 555. Ask for CMOS variant of 555, everyone will work. The most critical in this build are the headphones. Replacing them with something more common will be a challenge. You could replace them with some simple detector and amplifier.

[TH Jim]

Hi Guys,

I need some help from you guys about " Matchless Metal Detector Project" - in geotech website. The IC in this project is ICM7556IPD, it seem I cannot find it in my country. So, is there some other type of IC that can I use to replace it in this project? The author of the project also try TS556CN, it worked, but not as well - like he says, also, I cannot find this type of this IC either. Please, can someone help me?

Thanks.

Try any of the CMOS 555 variants (7555), most will work - although the detector won't!

[adiputra]

Hi Guys,

I need some help from you guys about " Matchless Metal Detector Project" - in geotech website. The IC in this project is ICM7556IPD, it seem I cannot find it in my country. So, is there some other type of IC that can I use to replace it in this project? The author of the project also try TS556CN, it worked, but not as well - like he says, also, I cannot find this type of this IC either. Please, can someone help me?

Thanks.