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tone generator and probe DIY?

PostPosted: June 22nd, 2012, 7:20 pm
by novex
could anyone provide a design to make a tone generator and probe for identifying/tracing a cable?

i am supposed to buy one for work but think making one would be more fun, however after a bit of googling the only instructions i could find were fairly vague or above my head. (make a square wave generator and coil some wire round a nail for the probe etc)

would be a neat project and as far as i am aware theres no decent howtoos for it floating around at present.

Re: tone generator and probe DIY?

PostPosted: June 22nd, 2012, 11:23 pm
by dkedr
You need to provide more detail.

What frequency or frequency range are you looking at?
What kind of wave form do you want?
How much power does it need to have?
How accurate does the amplitude/frequency/wave form have to be?


A simple 555 timer could do a square wave at a few MHz if you get a cmos 555. The voltage output would depend on your load and the supply voltage. Example circuits can be found in the LM555 datasheet.

If you want triangle and/or sine waves you will need to use a function generator chip.

If you need more frequency accuracy/stability you can use a crystal oscillator.

Re: tone generator and probe DIY?

PostPosted: June 23rd, 2012, 12:42 am
by novex
what i am hoping for is a usable version of something like this

http://www.amazon.com/Extech-40180-Gene ... B00023RVNO

that i can use to identify cables within a loom or pairs within a voice backbone cable etc.

the max distance i tend to trace is 90m

Re: tone generator and probe DIY?

PostPosted: June 23rd, 2012, 1:48 am
by dkedr
The datasheet says 1KHz square wave with a 6V amplitude approximately. I'm going to guess that 6V is peak to peak as the thing runs of a 9V battery.

So grab a 555, select the resistor capacitor combination(plenty of online calculators) to give a 1KHz signal, add some 9V battery leads, put a big capacitor in series with the output, and tada. You have your signal generator.

As for the probe, the nail with wire wound around it sounds like the thing to do. This is just a simple transformer, a terrible, but simple transformer. You would have to experiment with the number of turns. After you have your nail transformer you will need to amplify the signal. A little head phone amplifier might be enough, like the LM386.

And for any one else here is the datasheet of the tester from amazon: http://www.extech.com/instruments/resou ... 180_um.pdf

Re: tone generator and probe DIY?

PostPosted: June 23rd, 2012, 8:57 am
by st2000
As for the probe, the nail with wire wound around it sounds like the thing to do. This is just a simple transformer, a terrible, but simple transformer. You would have to experiment with the number of turns. After you have your nail transformer you will need to amplify the signal. A little head phone amplifier might be enough, like the LM386.


You should probably add a capacitor in parallel with the coil pick up you are making. For your purposes you want to make a resonator that "rings" at the frequency of the signal your are injecting:

omega = sqrt(1/L*C)

(Don't forget that: omega = frequency*2*pi)

And you want to get the Q (the ability for it to "ring" after being excited by the injected signal) as high as possible (which I think is):

Q = R*sqrt(C/L)

...(for a coils and capacitors hooked up in parallel, if I recall correctly)

These and many other similar equations were handed out for free during the first MIT 6002x class talked about here:

http://hackaday.com/2012/02/14/mitx-first-course-announce-6-002x-circuits-and-electronics/

Re: tone generator and probe DIY?

PostPosted: March 7th, 2016, 12:23 am
by rasha
THINKS for information



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