Falcon MD20

[dom44]

sorry guys this is the final ignore previous 2 lay files had to add the 78L05 to it



md20-final.rar

[homefire]

Can you post just the Copper Layer ?

[dom44]

[homefire]

Which one is the Last? Fixed for the Attached md20.rar ???

[dom44]

yes it is the the one marked MD20-final circuit board should be right now i just have to check last resistor values i used around VCO and this is the final values i have soldered in I would suggest some one check against the circuit diagrams as i had to reverse engineer some of it because of the changes i had to make.

[homefire]

Good STuff from You Sir. Thank You.

[chemelec]

I was just playing with this circuit on a Breadboard.
I Assume the first 2N2222 with the coil on it, Should show an oscillation of about 300 KHz, measuring after the 150pF cap?
I Can't get it to Oscillate.

[homefire]

Gotta hit it with a Defibrillator. 20KV 10uS Pulse. 10 Pulse Train Pulses separated by 40uS Delay. LOL Yea, dat should get the ticker ticking. Are you using PN2222 ? Some times they just don't act the same. T2 going to the coil , is T1 in circuit ? Maybe it needs the feed back to sing.

[chemelec]

I have both the First oscillator and second transistor with the two 1N34a diodes on the breadboard.
Also the T2, So T1, T2 and T3 all wired up.
I first tried it with 2N2222's and than with 2N3904's

My coil measures 145uh and also made that copper ring for it.

GOT IT GOING NOW, Bad Connection.

[homefire]

Centered the Two Pot's ? 3904's are better at singing . Reduce R4 and R15 a bit and see if it wakes up. Try it without the Ring first.

[dom44]

R5 the 10k trimmer is critical where it is set as it effects the wave form shape and amplitude at some setting will stop the oscillator completely from working that's as it should be. the correct setting is just as the sign wave becomes symmetrical and and just before it shuts off is the sweet spot and the the most sensitive setting for it. I used 2N2222 but any NPN will work.
If you watch the scope and bring a piece of metal close to the coil the wave form will totally co laps and it will stop oscillating when it is set right.
From the second version of this detector I am working on I can tell you the real secret to this detector is only that second stage amplifier marked T3 with out it its just a pin pointer, and the auto tuning T1 which resets the oscillator dependent on the output level, the
the oscillator is prone to drift and temperature sensitive the auto tune circuit keeps it in Check to a degree but you still get some drift so it is important to keep the oscillator transistor thermally insulated when you set the threshold if you blow cold air over the transistor will significantly shift the oscillator.

and no homefire T3 is not feedback it just grounds the base of the oscillator shutting it off dependent on the DC level after the dc rectifier stage as set by the R10.

[dom44]

sorry homefire T1 shuts off the oscillator and acts as an auto tuning stage T3 is just a high gain amplifier stage with DC rectification. T4 acts like a comparator stage to set the trip point to activate T5.

[homefire]

Thank you . I was thinking it was some positive feed back.

[dom44]

that's cool I have had some time playing with this thing it is dead simple really and has lots of room for improvement, I am playing with a few different oscillator designs to find something more stable than this one, at the amount of amplification going on here a few Hz makes the tuning difficult to keep on track and as i said thermal insulation of the oscillator transistor is important.
maybe when it is in its case completed its enough to keep it stable but on the bench just air movements can effect it.

[homefire]

Get Crazy and Use Darlingtons. LOL