From: firstname.lastname@example.org (Ben Bradley)
Subject: Re: A Simple Circuit Design Challange
Date: Fri, 25 Oct 2002 15:20:10 GMT
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In sci.electronics.design, Dan wrote:
>I have a bit of a challange for anyone willing to take a stab.
>Design a circuit that will have a three conductor input port (In1,
>In2, In3) and a three conductor output port (Out1, Out2, Out3). If a
>user plugs a three conductor cable between these ports, the circuit
>will then detect two things.
>First, it will detect continuty between In1 and Out1, In2 and Out2,
>and finally In3 and Out3. At the same time, the circuit will detect a
>short circuit between either of the three, In1 and In2, In1 and In3 or
>In2 and In3. The indicators for detection on any of the six functions
>above would be LEDs. The circuit will be of minimal components and as
>simple as possible.
Makes me wonder - is this homework or a design for a high-volume
commercial product? And if it's homework, will your instructor use the
best design for a high-volume commercial product?
It's obviously a cable tester, and could be used for many types of
cables depending on what connectors you put on it, but especially
those terminated in 3-pin XLR connectors and 1/4" TRS phone plugs, as
are commonly used in sound studios and PA equiment for microphones and
line-level interconnects. These things sell for, I forget, maybe
$20-$30 at the big musical instrument chain stores (Mars, Guitar
>Anyone have any ideas?
Yes, and I see others' responses, but I'd put more effort into it
if...oh I don't know what...
Here's my idea, though you may find it too complicated, or maybe
even too expensive (and exact circuitry and implementation are left
"as an exercise for the student"): I've seen a microcontroller
advertised for less than 50 cents. If you have any budget left you
could even add a "cable capacitance is very high" LED.
Okay, you've twisted my arm and I'll give away of the store. :) Put
a cheap piezo speaker in it. Have the controller send out a 1760 Hz
(doubles as an "A" note tuner) square wave tone to the speaker when
all connections are OK, and sample all connections at every cycle of
the tone, so it stops for an intermittent connection. This way someone
can plug in a cable, jiggle it around, and feel confident it doesn't
have an intermittent open or short.