Falcon MD20

[jtz54]

Ok. The above issue with threshold has been fixed. The coil wires on connector were swapped (red wire is shield and gray wire center conductor-weird).
The unit seems a bit more stable with a bit more depth but field testing it over the next few days.

[jtz54]

Finished replacing ceramic caps with poly ones. When comparing this to another unit I'm thinking there's something else wrong in the circuit. While it does detect metal ok, trying to adjust the threshoild is near impossible. On a working one you adjust external pots until you barely hear a tone then when using the probe it sounds off when going toward metal OR sounds off when pulled away from non-metallic minerals like black sand. Although the range is very short, typically under 2", it is very useful in finding hidden gold inside of rocks. So I need to start trying to figure out why mine cannot adjust the threshold (either off or on but can adjust to the edge of just sounding off). Any ideas on troubleshooting or maybe adjusting the trim pots inside?

[jtz54]

Thanks Mick! I will start with the caps and report back to this thread.

[Mechanic]

HI Jtz,

For a start I would try replacing the ceramic disk capacitors with either SMD np0 caps or through hole polypropylene or polyester caps. Those ceramic disk caps will change their value dramatically with temperature change. The other trick to narrow down exactly where the main drift is occurring would be to heat up the components individually, that way you can narrow down the temperature sensitive areas.

Cheers Mick

[jtz54]

I have the Falcon MD20. It has a 555 chip in it for (I'm assuming) the audio output. I really like the unit but it is a bit unstable during use and has to be constantly adjusted. I don't think the auto ground balance pot is that, think it's a threshold adjustment as is the 500K sensitivity pot. I added a 50K ten turn pot in series with the 500K pot and the unit becomes more stable and I'm able to adjust the threshold to a much finer degree. Any other suggestions to improve on the design?

[Pacliff1985]

that's what I needed to know. Thank you

[Qiaozhi]

good job and thank you for your schematics. I've been researching information on this metal detector for quite some time and try to see if I could duplicate it I was looking at the schematic and I was wondering what type the capacitors are NF, UF and so on. maybe it's obvious I'm just missing something somewhere..

Thanks in advance

I assume you're asking about the capacitors marked "0.01" and ".018".
If not specifically stated, then these values are in uF. For example, "0.01" means "0.01uF". Or in other words, "10nF".
Likewise, ".018" is "18nF".

[Pacliff1985]

Here are the values for the pots and trimmers. This is for the MD 8, current model is MD 20. The probe is a 3/8" ferrite core probably 20 to 40 turns of AWG 32? These must be good for something, I believe mine is from the 1980's

good job and thank you for your schematics. I've been researching information on this metal detector for quite some time and try to see if I could duplicate it I was looking at the schematic and I was wondering what type the capacitors are NF, UF and so on. maybe it's obvious I'm just missing something somewhere..

Thanks in advance

[parun14]

Need halp for PCB !

[Ism]

Thank you, I have been trying with DipTrace but my board looks like crap compared to yours.

[Constantin]

If anybody has developed a PCB layout for the schematic that was made available in this thread, would you please post it.
I am gathering components to build this project and have never successfully used a PCB layout design program.

Just an idea without silent switch.

[Ism]

If anybody has developed a PCB layout for the schematic that was made available in this thread, would you please post it.
I am gathering components to build this project and have never successfully used a PCB layout design program.

[6666]

I recently found this good video on MD20, may try and make it, (well add it to the list)

http://www.youtube.com/watch?v=rRiSZ_2AyTI

[nelson]

Here is a good video that shows how it works.

http://www.youtube.com/watch?v=OFNbPbAdvGE

Regards

Nelson

You cannot watch a film on their website -> http://www.falconmetaldetectors.com/
but you can buy the T shirt ... and a cap!
Looks like they have a lot of distributors around the world for what is essentially a very simple design.

[homefire]

WoW! Thank You Sir!