|Quote:||Posted by yem22|
i'm windering how deeply it has been improved, i made it before 3 days , but it is the same as they said that can detect a coin from 120 mm,
please help !!
What diameter is your coil? A larger diameter will go deeper, but you may lose sensitivity for small objects.
If your oscillators are super stable, (no drift,) you might try something like a flip-flop phase detector, but put a meter on its output, instead of your ear, it will have a small degree of increased sensitivity, using the little 3 1/2 digit decimal meters, even amplify the voltage change and apply it to a VCO to get audibly increased sensitivity. AND isolate the 2 oscillators, more.
I have a number of SA612 ICs which are an improved SA602, they have a doubly balanced mixer, on board which will prevent any interlock, and unwanted interlock destroys sensitivity.
The on board oscillator can be used as a straight amp, by using a .1 uf cap, from pin 7 to ground and another to input the search osc signal to pin 6. The reference osc pins are 1 and 2, of which, use a .1uf to bypass pin 2 to ground and another to input the reference osc sig. to pin 1. The mixer tone OR voltage is taken from pins 4 and 5. If tone, use 1 uf caps on both pins and use a center tapped transformer, or an op amp to use this signal. Pin 8 is + v, pin 3 is ground, and use an 78L08, or 78M08 regulator as max volts is 9v. Of course if you run the rest of unit on 9v, you can run the mixer on 9v too.
If you want to measure voltage change, it is a bit more trouble. Use one pin, like 4, grounded through a 22 or 33 ufd electrolytic; lead 5 goes to a similar cap, this cap then goes to a diode pair (doubler) to get a dc voltage. Of course, now a single input op amp can be used with variable gain. This voltage can go to a meter and a VCO.
I will do a small drawing and upload, but it may be a few days as I have a bug and do not feel that great.
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« Last Edit: November 27, 2009, 09:14:31 am by goldigger »