Audible Continuity Tester

Way back in 2000 (this is being written in March 2008) I ran across a neat little continuity tester in issue #1 of the now defunct Homebrewer Magazine. It was in the Test Topics column written by Joe Everhart, N2CX. Little did I know then that our paths would cross at OzarkCOn 2007. But thats another story, and a good one too.

In his column Joe discussed a little piezo buzzer for continuity testing and then mentioned this circuit as a "tad more complex but much more versatile. It's an audio oscillator, puts less than 1 ma through the circuit under test, has plenty of volume, and can check not only continuity, but also diodes, electrolytic caps, and will give some idea of resistance due to changes in the tone pitch.

I use it often for checking shorts between IC pins on circuit boards, and also for continuity through the solder joint between the pin and the board. With only ~1 ma through the test leads I know I'm not going to damage any device in the circuit. I can't recall when I built it, but it must have been around 2001 or 2. It's been on the bench so long that I feel like something is wrong if I don't see it there.

Check out the enclosure and you'll see why I affectionately refer to this little tester as the Spaghetti Tester. It's become one of the, most used items on the bench. No need to look at digits or needles, just concentrate on placing the probes, and listen for the tone.
The schematic for this little jewel is here.

Revised 7 Dec 2012
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