From: firstname.lastname@example.org (Tom Bruhns)
Subject: Re: Short Circuit Detector
Date: 11 Oct 2002 17:07:27 -0700
NNTP-Posting-Date: 12 Oct 2002 00:07:28 GMT
I have one I've used for years (and happen to be in the process of
re-vamping to use more readily available components). It's very
simple. In the configuration I _normally_ use, it injects a current
from a 1.5v cell through a 1k resistor and a diode, so the
short-circuit current is about 1mA. The voltage across the "short"
converts to a current to drive an oscillator, so the higher the pitch
the shorter the short. With it I can hear the difference between 1
ohm and a dead short, about 1mV delta. BUT...if you inject a current
from an external source, you can use it to find where in the circuit
the drop is the lowest: the point of the short. So with an amp
excitation, you can hear milliohm changes. The circuit is currently
an A77 watch cell (or similar 1.5V), 2 pnp transistors, 2 npn's, a
tiny audio transformer (Mouser TC001), and as tiny an 8-ohm speaker as
you can find, and a very few R's and a couple C's. When not
connected, the current drain is less than a microamp, so no on-off
switch. The one I've had a long time draws a lot more "off" current,
and even so the AAA cell lasts over five years.
I'm planning to make the circuit available through the Wenzel web site
(where there are a few other neat little test circuits) eventually,
but could perhaps give it limited distribution before that.
"red rover" wrote in message news:...
> Does anyone have link to a design for
> short circuit detector? I recall that Bob
> Pease had a design for one in his Analog
> Troubleshooting book. I believe it was
> basically a micro ohmeter with an audio
> output and you worked your way around
> the pcb homing in on the fault.
> Anybody here made one? Any good success?