A Failed Idea

There was a request on an email list I subscribe to for a way to measure 50 uA currents without having to put a meter in series with the circuit.  The idea was to spot where the current was being used that was draining the battery too quickly.

I thought of using an old, broken cassette player like this:

(how was life possible before cheap phones that could play/record digital files?) - it senses the magnetic field recorded in the magnetic particles on the tape and since all currents have accompanying magnetic fields maybe a cassette player could be used to sense them ?  Of course since the current is DC the cassette playback head would have to be moved across the circuit board trace to register anything.

I tried using a wire moved around a stationary cassette player head - no dice.  This was a fairly thick wire carrying 7.5 mA or 7500 uA so no chance of detecting 50 uA.  Thinking about it later anyone who has played a crinkled cassette tape knows that unless the tape is in firm contact with the head the amount of sound is decreased by a lot.  So I probably should have tried a smaller wire with thin insulation like magnet wire and have it actually touching the head.

Still I doubt it would work, the magnetic fields in question are probably just too weak to use this idea.

So, even though no one likes to report a fail, it didn't work - but it was worth a try !


Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm