Falcon MD20

[Carl-NC]

It's a classic "energy theft" design, covered in Ch 9 of ITMD3.

[Teleno]

Been following this thread off and on for years. There are certainly some knowledgeable people on this forum! Can anyone provide a circuit theory of operation for the MD20 as it stands today? I think that would help a lot in understanding where possible improvements can be made.

Thanks!

It's a Colpitts oscillator, the amplitude changes depending on the magnetic coupling to the target. The sine wave is rectified to produce a dc level and modulate the audio signal. The frequency changes too but that variabke isn't used.

[jtz54]

Been following this thread off and on for years. There are certainly some knowledgeable people on this forum! Can anyone provide a circuit theory of operation for the MD20 as it stands today? I think that would help a lot in understanding where possible improvements can be made.

Thanks!

[Qiaozhi]

According to forum etiquette, posting in all capital letters is equivalent to SHOUTING.
It also makes the post difficult to read.

[haydarpasha]

I WANT TO STATE FIRST THAT I HAVE NOTHING TO DO WITH ELECTRONICS.
I AM INTERESTED IN MINERAL STONES AND I LIKE FALCON SERIES TRACKERS. BUT I DO NOT HAVE THE POSSIBILITY TO PROVIDE IT IN MY REGION. THAT'S WHY I RESEARCHED AND FOUND GEOTECH1 AND THIS FORUM. I REVIEWED THE POSTS ON THE TOPIC.
FIRST OF all, I would like to express my RESPECT TO EVERYONE WHO CONTRIBUTED, INCLUDING ALTRA, DBANNER, GOATY. I SUPERPOSED THE 3 PCB IMAGES FOUND IN THE FORUM. PCB (DIY), PCB (WALKMAN) AND PCB (MD20 ORIGINAL). I ADDRESSED THE THREE PCBS WITH THE SAME NUMBERS. I JUST FOUND THESE DIFFERENCES.
1) IN PCB (DIY) STUDY, THE CONNECTION BETWEEN C5 (92) AND (19),
2) IN PCB (WALKMAN) STUDY, CONNECTION BETWEEN C5(92) AND (19),
3) IN PCB (WALKMAN) STUDY, CONNECTION BETWEEN Q2(87) AND C8(23),
4) IN PCB(WALKMAN) STUDY, CONNECTION BETWEEN BAT1+(36) AND 555(55),
5) IN THESE TWO STUDIES, SENSIVITY CONNECTION WITH (1, (19), (20) ENDS,
6) IN THESE TWO STUDIES, GND-BAL CONNECTION WITH (29), (30) TERMS
AGAIN, WHEN THE ORIGINAL PCB (MD20 ORIGINAL) IMAGE AVAILABLE ON THE PLATFORM IS ADDRESSED, IT IS OBSERVED THAT THE ABOVE ISSUES ARE DIFFERENT.
I NEED EVALUATIONS ON THE ISSUES I MENTIONED ABOVE IN ORDER TO CONCLUDE.
HAVE A GOOD DAY TO EVERYONE. KIND REGARDS

[kt315]

Can somebody guide me with the correct schematics for a workable falcon. my ferrite coil is 150mH & 1 ohm resistance. I am using 2N2222 transistors with NE555. Continuous vibrating sound is coming from output of 555 but nothing seems working.. can somebody help?

FALCON has a specific tuning on threshold. by copper ring on a housing you move it along and tune on sound.
you have to know sure this fact BEFORE to copy the detector.

[sunita.pradhan]

Can somebody guide me with the correct schematics for a workable falcon. my ferrite coil is 150mH & 1 ohm resistance. I am using 2N2222 transistors with NE555. Continuous vibrating sound is coming from output of 555 but nothing seems working.. can somebody help?

[idigit]

calling Falcon .. sometimes if u repeat call 'they get your number' - like i had one unit , then i got another unit ..
called about the 2nd unit, woman picks up says 'call back in 30 minutes' .. call in 30 minutes and get answering machine ..

[Matt_Rowe]

Does anyone who built this newest version, the 20, sell the pcb and compnoents as a kit, i called Falcon since they live in my city, they said the md8 would pick up about 1 inch in soil, the MD10 2 inches, and MD20, 3 inches. The only difference in 10 and 20 is depth.

[Altra]

I agree on all of your corrections. The big mistake was the 3906, and yes reverse the emitter collector for the mps5172. Also the led needs reversed. Get a rough schematic and I can fill in the pot values and cw/ccw connections. Most of the trim pots are set near mid-point.

[dbanner]

Altra, please check the orientation of your MPS5172(shown as 2N3906 on schematic). Please verify that the emitter shown on your drawing is indeed the emitter, as the schematic shows the emitter and collector swapped. This is the only thing remaining to be checked before I can finalize the schematic.

[dbanner]

And finally, a 10uF electrolytic capacitor from collector of MPSA13 to ground. Missing on the schematic, I have added it in.
Well that looks to be it. Now I can redraw the schematic to include all the changes.

[dbanner]

Yet another correction, this time a 10n ceramic capacitor just before the MPSA13, omitted from the schematic. I've now included it. Highlighted again in a red box. I'm going through the circuit step by step, to illustrate just how easy it can be to just have a tiny error or a missing component, and the circuit is kaputz.

[dbanner]

Moving right along, I found another error, this time a 10n bypass capacitor omitted from the schematic but is on the actual pcb. I have now included it on the schematic. Right near the red box, on the emitter of the transistor, there is where it should be.

[dbanner]

1 I did not forget, I wanted verification knowing there were mistakes on the original.

2 The schematic I posted was drawn in 1995 when I posted it 15 years later as favor to the forum. Had no idea it was md2020 or an md8

3 ^%*^%*

4 buy your own, destroy it, and post a perfect schematic

Splendid, Now having gotten that out of the way, I wish to point out that on the schematic, one leg of the trimmer should be connected to its wiper, as shown in the attachment, highlighted in the red box. When all corrections have been made, then a final schematic can be drawn.