"Tone-Ohm" type of instrument...

[Externet]

Is there a schematic diagram of a "Tone-Ohm" type of instrument of your suggestion, available somewhere in order to build one myself ?

Or a kit ? What are the principles of operation circuitry ? Does it has anything to do with Weathestone circuits ?

 

[Kripton2035]

here : on the part " output with sound"
**broken link removed**
regards,

 

[Externet]

Thanks. A nice collection !

 

[Audioguru]

Some people who hate music are completely tone deaf. They cannot hear that one tone has a higher or lower pitch (frequency) than another tone.
I love music and studied it when I was young. I played a trombone in my high school band. Our band went on tour for contests and won many of them.

More than 50 years ago I was working on getting the ability to have "perfect pitch" where I could identify or produce the accurate frequency (the exact pitch) of a sound and almost got it but I gave up studying music and didn't reach it. Some people are born with perfect pitch so their hearing, singing, whistling, musical instrument playing and brain become an accurate signal generator and frequency counter.

A Tone-Ohm device would change the pitch of its tone when the very low resistance of a short circuit becomes closer to its probes.

 

[Externet]

Now I realize I was imprecise with the "tone-ohm instrument" titled post. Sorry. Should had been better as "tone-ohm continuity test instrument"
Yes, I have one, the 'Excelta MB-1' and am curious about others. ----> https://s588.photobucket.com/user/Innernet/media/P1010196_zpscbfb7439.jpg.html

 

[betwixt]

The Excelta is a continuity tester, not quite the same as a "Tone Ohm", it will beep whenever enough current can flow between it's probes that it can start to oscillate.

A real "Tone Ohm" device works on a different principle, it uses 4-wire measurement. The idea is that each probe has two wires to it, one wire to each probe carries a constant current at low voltage. I can't remember what the original testers used but it was something like 0.1V at 10mA, in other words low enough that it wouldn't damage anything or make semiconductors start to pass current. The other two wires took a voltage reading which was then amplified and sent to a digital readout and an audio oscillator. The probes were made from standard audio screened cable, the current feed went through the outer screen and the measurement came back through the inner wire.

By using this method, the resistance of the probe wires and connectors was eliminated from the measurment, on a standard DVM these could account for most of the resistance and they would hide the tiny resistance you were trying to trace. They were accurate down to a few milli-Ohms so you sould easily measure the resistance of even quite short lengths of PCB track. The audio tone was controlled by the measurement and it's pitch went higher as the resistance got lower, it allowed you to follow traces toward a short circuit without looking up at the digital readout. The probes were moved along traces near the short and a rise in pitch meant you were getting nearer, a fall meant you were heading away from it. The short was obviously at or very close to the point with highest pitch. They were/are very useful tools.

Brian.