emf meter project

Posted on Feb 6, 2014

Look at the left side of the circuit (sensing coil and op-amp). When I wired mine the way shown in the schematic, it wouldn`t pick up anything. I didn`t have a 1mH radial inductor handy, so I fashioned my own using 30ga enamel wire and a round core (100 turns or so, give or take). But, if I disconnect the side of the coil going to the + input on the op amp in the schematic,

emf meter project
Click here to download the full size of the above Circuit.

leaving it free floating, then I can pick up fields. So, in essence, it`s acting more as an antenna than an inductor. Any thoughts on this Maybe I need a better coil My 2nd question: the circuit is a LOT more sensitive if I connect it to an earth ground, such as when I connect the grounding clip on my oscilloscope when taking readings. Any thoughts on this Since I intend this device to be portable, I can`t be earthing it all the time. At present I`m using a TL082 op-amp, but I just got my hands on some LMC6482 CMOS rail-to-rail op amps. Do you think that one would work better for this I went with the rail-to-rail so I can get a better range in the comparator portion in my circuit, not in the schematic above. I am using a Basic Stamp 2 feeding one side of a comparator with a filtered PWM signal, and the other side is a filtered and amplified version of the EMF signal, and the uC uses successive approximation to determine the signal level and it lights up the bargraph display and beeps a piezo transducer based on its measurements. Ha ha guys. I`m not doing it professionally. nor am I attempting to con anyone or make myself famous on TV. It`s just one of my dozen-odd hobbies I partake in, just like electronics. Aside from ghost hunting, EMF meters can be handy for identifying live wires inside walls as well. You know, before you drill a hole and hit a live 120V line, making your eyeballs light up like a Christmas tree. I just...

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