I spent some time servicing hard-wired alarm systems in a number of different types of buildings. I had the same problem trying to find the run of the four-wire cabling to the sensors on doors, windows, and other vulnerable entry points.
To solve the problem, I built a simple oscillator using a 555 timer chip. The output was a square wave of about 1KHz. This 1KHz square wave was rich in harmonics way up to the MW broadcast band and was boosted by a beefy transistor. The transistor’s output was fed into a step-down transformer out of an old transistor radio.
The low-impedance output of the transformer was fed into the run of line from the main control panel. A small transistor radio tuned to a blank space on the dial easily found the run of the cable and showed not only where the cable ran behind the wallboard or ceiling, but it also found any break in the cable running to the sensor. It was not complicated, not fancy, but it certainly worked.
This entry was submitted by Clive Hollins and edited by Rob Spiegel.
Tell us your experience in solving a knotty engineering problem. Send to Rob Spiegel for Sherlock Ohms.
I guess this all depends upon several factors Tim.
1) Materials on hand
2) Speed of which to find the issue
3) The enjoyment of making things
4) Nothing else to do
If I already have the materials on hand, it would not take that much of my time to create this and put it into use. However, if I have to hunt for the materials to build this, and then order anything missing, the delay in that will of course offset the cost of the already made unit. But this brings up #3 however and the pure enjoyment of taking raw components and making a useful object, test device, whirlie-gig, etc... out of them.
Umm, you guys do know that you can buy a decent tone generator/wire tracer for around $50, right? I know that's more expensive than making one, but your time's gotta be worth something.
Great solution. Years ago, I actually remember one of my classmates doing something similar as a demonstration in an Electromagnetics course. However, this as just a demo of the principle with no actual application. Great example of engineering in the real world!
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