Low-voltage, low-current continuity tester

[gdewitte]

Many years ago (sometime in the last century), I built a continuity tester from a kit (which may have been from Audio Amateur), but can no longer find any info for it. The tester still works fine, and I frequently use it. Its PCB is labeled PE301A, uses an LM324 with a buzzer, is powered by a 9V battery, fits nicely in a 2.75"×4" black plastic box, has Voc = ~ 200mV, and Isc = ~ 270µA. Before I start tracing PCB tracks to reverse engineer this tester, and satisfy my curiosity about its operation, does anyone recognize it and perhaps have a schematic? Lots of web searching has not turned up anything.

[hli]

It might be similar to the one Conrad still sells: http://www.conrad.com/ce/en/product/199842/Conrad-Continuity-Tester-PCB-Kit#download-dokumente. This ones uses a LM741 for continuity detection and a CD4093 for driving the piezo buzzer. I own this one since about twenty years or so... Unfortunately there is no user manual in English, but at least it contains the schematic (page 21, value on page 15).

[Wh1sper]

Hint: https://www.eevblog.com/forum/testgear/multimeter-with-low-continuity-test-voltage/msg480122/#msg480122

With only 1 diode one are able to drop the voltage down to the diode flow voltage. In my case a Germanium Diode = 0.4V

[electronic_eel]

Here are a bunch of continuity tester schematics collected:
http://kripton2035.free.fr/continuity-repos.html

Maybe your schematic is in there too.

[Wh1sper]

Here are a bunch of continuity tester schematics collected:
http://kripton2035.free.fr/continuity-repos.html

Maybe your schematic is in there too.

Nice Site, thanx!