Hi All. This is my first post here. I have been having a heck of a time with what I thought would be a fairly simple task. Unfortunately, I don't know much at all about analog stuff, filters, etc. Days of head scratching and Google-ing have landed me here.
I am a little off-topic because I am not using a transducer, but everything else suits this thread. The threads I found about buried wires had no useful info.
I am trying to do a variation on the buried wire thing.
I found this circuit a while back and breadboarded it. In the wire I am using a 40 khz square signal originally generated by a spare PWM on a AVR micro.
**broken link removed**
I substituted an LM358 for the 348 pictured as well as the resistor and cap to set the freq of the 567.
I am using a telephone pickup coil for the sensor, although I'd like to be able to use an SMD inductor if possible.
It did not work at all, I now think the amp section is tuned for a freq other than 40khz. I read up some and modified it to a simple 2 stage amp, but with much too high amplification. Despite this, it worked well on the breadboard. I did a PCB for it and shrunk it down to about 19mm square.
It still picks up the wire, but now also scissors, pliers, nails, etc. I think it is picking up the internal signal from the 567.
Can anyone share a +5 volt circuit that will detect the wire loop, and just as important, not detect it when it is not near.
Is it possible to tell from the schematic if the op-amp is tuned for a certain frequency? I don't need to use 40khz, anything over 8khz should be fine.
If it matters, it will be used in a remote control car.
Any ideas are greatly appreciated. This is one part of a much larger project and I can't spend much more time on it alone with my limited knowledge in this area.
Thanks in advance,
Craig