This circuit perhaps isn't strictly 'Home-Brew' as I certainly didn't design it. I don't know who did as I found the circuit in an electronics lab when I was at college. This was a photo-stat of a photo-stat... so I've re-drawn it.
It has far more uses than the usual testing of fuses &c and even gives a pretty good guide to the state of capacitors.
There's no need to get hung up on the speaker impedance as over the years I've used everything from 8Ω to piezo transducers.
Mine has got an 80Ω one along with a socket so I can use this a high (ish) impedance test speaker. I've also added another one so I can use the tester's output as a crude signal generator.
Basically the higher the tone it makes the lower the resistance it's testing. Very high resistances will produce a series of pips and it's surprising how it can be pipping every couple of seconds on things that other meters have read as infinity.
I've had one for twenty-five years now (Tempus Fugit and all that) and found it immensely useful. There's an audible continuity tester on my DMM but I don't like it because it's too quiet and... well... digital in that it either bleeps or not.
I hope other people find it of use.
Joe
It has far more uses than the usual testing of fuses &c and even gives a pretty good guide to the state of capacitors.
There's no need to get hung up on the speaker impedance as over the years I've used everything from 8Ω to piezo transducers.
Mine has got an 80Ω one along with a socket so I can use this a high (ish) impedance test speaker. I've also added another one so I can use the tester's output as a crude signal generator.
Basically the higher the tone it makes the lower the resistance it's testing. Very high resistances will produce a series of pips and it's surprising how it can be pipping every couple of seconds on things that other meters have read as infinity.
I've had one for twenty-five years now (Tempus Fugit and all that) and found it immensely useful. There's an audible continuity tester on my DMM but I don't like it because it's too quiet and... well... digital in that it either bleeps or not.
I hope other people find it of use.
Joe
