Falcon MD20

[karim1980]

i placed a resestor 1moh in this place (?) but i dont get the sound . when i touch the pcb from behind i hear the sound
and i have made MD20 with 555 but is the same problem no sound

[dbanner]

How did you wind your coil? This could be problem.

[karim1980]

thank you dbanner
coil= 140uh 2 ohm 60t ferrite =1cm/5cm wire=0.20mm

[Tim]

Upon further scrutiny, there are many discrepancies between the 4093 version and original schematic. 2n3906 base goes to gnd via 33uf & GB trimmer on original, but bc557 to + via 680k & 220uf on this version. There are 2x 500k pots & 10k/100k trimmers on this version, but original shows 20k GB pot, 10k sens pot & other 10k, then 2M, 1M, 100k & 10k(sens) trimmers. There are 4x2n2222s & MPSA13 on original, but 7x2n2222,bc327(mpsa13[?]) & bc557(2n3904[?]). However it seems the 557/327 & 2x2n2222's are related to the vco, and 2n3904 has been replaced by 2n2222. (???!!!)
I would suggest start with original MD20 schem then replace 555(and surrounding components) with 4093/vco if desired. However I can see no advantage in vco on this on/off detection system. There is no active or audible threshold to warrant it. It simply sounds on approach to non-ferrous, and on retreat from ferrous. It is an invaluable tool for detecting pin-prick specks of gold in pannings or rocks.

[dbanner]

there is video posted in this thread which shows varying pitch vco when detecting metals, with proximity of gold, pitch is very high. the circuit board in the video does not use 4093, so i'm not sure. I'll have to re read entire thread to be sure how circuit evolved. will have more to say tomorrow.

[karim1980]

I will made the original version with 555
I need pcb layout For this version please

[kt315]

i need. share anybody 555 original board version with high resolution, under light.
also checked PART LIST.
please rule http://www.geotech1.com/forums/showt...here-share-out
please DELETE a flux from back side by alcohol before to do the pics.

tia

[homefire]

There was no 555 in the original. D-Falcon[1].pdf

[Tim]

This IMG and Lay6 is the best version I have. Schem is NOT MD20 but MD8 (pre-555).

[kt315]

Homefire, i see two versions. 'old', without 555 and 'new', with 555. there is not full schematic with 555.
look karim's pic. thats new revision.

[homefire]

Gary did this one.

[Wahyu]

[dbanner]

This was posted earlier in the thread. MD-20.

[Wahyu]

MD20Falcon eaglecad sch and brd

MD20Falcon.zip

[dbanner]

Coil info?