Resistance = Pitch Tool [R value = Frequency of audio Tone] for quicki debugs ?

[petemoore]

  I'd like to have an R meter which ranges from 1k - 1meg,.
 It would introduce a frequency dependent upon R value, which feeds to an audio monitor [amp/transducer.
 In this way ballpark resistances could be ranged very quickly and without having to look at a DMM screen.
 Anything below 800ohm could be tuned to produce a frequency below the transducer range.
 Anything above 1meg could be tuned to produce frequencies above say 18k.
 ie a resistor value produces an oscillating pitch, and a FF resistance set could play a 'song', any wrong notes [say a very high pitch where a low one is expexted...probelm found.
 You're welcome to help me design or find it !
 Basically just a ''potentiometer theremin'', somehow tuned to have a nice even frequency sweep of fairly wide audio range controlled by R values between say 1k and 1meg.
 Perhaps high impedance inputs for the R under test would be needed for in circuit testing ?
 I think a fairly accurate pitch memory might be quickly developed, enough at least to know a 1meg range from 820k, most of the time I'm looking for an R value of 'something big' or 'something small' or 'anything there at all' in terms of resistance checking, for more scaled, precise measurements of course the DMM can be set up, connected and the screen can be read as long as the probes don't move.

[PeterPan]

Here's a possible approach. There is an old IC chip, a, 8038 Function generator, which I have found to have a pretty linear relationship between voltage input and frequency output. Using that as a building block, you could set up a constant current source whose output would go to your resistor under test, and the resulting voltage drop would then feed the voltage input of the 8038. You'd need some calibration pots,and you'd want to tune it so that infinite resistance generated 20Khz (above what you can hear), and zero ohms generated around 20hz. The constant current setting would also need to be tweaked so that the pitch range matched what you expect to hear for various resistances. Such a circuit would not be very precise without careful tuning before each use. But it doesn't sound like you need musical quality pitch accuracy anyway. Just one possible approach.

[merlinb]

   Anything above 1meg could be tuned to produce frequencies above say 18k.

How would you hear it?

[samhay]

^  I think a fairly accurate pitch memory might be quickly developed

If your goal is to also help develop relative or absolute pitch for musical purposes, then you probably need to do some more work so that each resistance (or resistance range) gives you the frequency of specific musical notes.
i.e. you want to output 82, then 87Hz, but not 83Hz.

[Ben N]

   Anything above 1meg could be tuned to produce frequencies above say 18k.

How would you hear it?

Get a dog. Or a teenager.

[electrip]

Practical approach:
one decade of resistance per octave should project everything between 1R and 10M into the audible range.   

electrip

[anotherjim]

CD4046 VCO. Probably best to use the tuning resistor pin rather than the control voltage (more range). A triangle wave can be developed off the tuning cap which would be kinder on the ears.

[petemoore]

one decade of resistance per octave should project everything between 1R and 10M into the audible range.
That would be nice to try out !
Once up and tunable, ithe R=F ratio would be up to the user to set. A couple permanent 'set-up-range' resistors [one low R/one high R] in a tunable circuit would make it pretty easy to get it up working in a familiar way.
Yupp, 20khz is above hearing, perhaps the contact would produce a transient tone that could be recognized as 'really big value'. this is intended to for zip bug finding, measurements or problems can be deferred back to the DMM for more detailed or precise information.
Another form of information feedback that DMM's can't provide is the 'sound' of contact being made or lost, instant feedback to help know when a resistor under test is connected in the measuring circuit [you lost your connection there for a few nano's would cause a pitch change].
A 'soothing' waveshape during debugging would be preferred.
 

[anotherjim]

Actually, any method using the test resistance as the oscillators timing resistor will give inverted operation - low R - Higher f. That would be the simplest if you can live with that.

I can remember a piece of test equipment called a "Bughound". It could help you find locate short circuits by producing a test tone dependent on resistance - and sensitive to fraction of an ohm.

[R.G.]

A while back, I got off into opining about the design of a continuity tester, kind of the inverse of a resistance tester, and oriented towards finding low ohms, not all ohms.  See: http://www.diystompboxes.com/smfforum/index.php?topic=106242.0

Also, you need to be somewhat careful about what you use it for. It's hard to tell what resistor is what during in-circuit testing because there are things in parallel. It gets worse if the "things in parallel" include big caps (would make a changing pitch as they charged) and semiconductor junctions. Depending on where you're connecting the two probes, you might forward bias a semiconductor junction if the tester uses more than about 0.4V for silicon and 0.1V for germanium junctions. So you might want to test only at quite low voltages to keep from turning junctions on for falsely low readings if resistance is what you're after.

I'm nearly always wondering more if the resistance between two points is nearly zero or not nearly zero during debug.

[Johan]

Search for voltage to frequency on Google.  There are chips designed for this.  With a 1
M going from voltage to input and your probes from input and ground,  the resistor you're probing will form a voltage divider with the resistor from voltage. And the chip will output a corresponding frequency
J

[PRR]

"Talking Resistor Calculator speaks to tell you what the value of your resistors.."
http://www.gadgetgangster.com/news/56-jeffs-shop/548-talking-resistor-calculator.html

Basically one part, a Propeller CPU proto-board. (And an "amplified speaker", but you all have several of those.) However you do need to get up to speed with pushing code onto the CPU board. I picked it up (on a Stamp) pretty quick, but it isn't a musical-type skill.

hmmmmm..... looking at the code, it is a dumb if/then case with a very limited set of values. It cries for simple refactoring. Also a sample-to-Ohms computation so it can say "any" value, not just the ones in (or added to) the code.

Apparently the "talk" function is built into the Propeller (yay!!) but the coder felt he wanted to optimize the pronunciation with mis-spelled phrases like "wun~ hundred fiftee oahm resistor".

[petemoore]

 Even with a parallel cap 'interfering with' the resistance [perhaps a sweep would tell if there's a cap in there and give some idea to the value, other computable or 'feel' information about capacitor time based response], a DMM can be called into service, reliably, the marks on the resistor show the near-actual Rvalue.
Alternately, expected ''capacitor sweeps'' could be ignored except where resistance was otherwise called into question.
  The power requirement [ie introducing current] in a circuit pretty much negates use unless it can be ignored or gotten around.
  Somehow the DMM's manage to try to Read R's while they're in circuits [without damaging them], perhaps there's a way to get an analog signal out of the number generator, or somehow source a signal from an analog multi meter driving circuit to another amplifier.
   

[PRR]

> Somehow the DMM's manage to try to Read R's while they're in circuits [without damaging them]

The modern DMM is a 200mV (0.2V) instrument. It doesn't hold more than 200mV across its inputs for long.

200mV is safe in 1/4W resistors down to 0.16 Ohms.

Most of these DMMs don't even try to read sub-Ohm resistors. They put 1mA maximum into the resistor. This will read 200 Ohms as 200mV, 10 Ohms as 10mV, and ~~1 Ohm parts as a bobble around 1mV.

So the maximum Power out of the probes is 200mV*1mA= 0.000,2 Watts.

An amusing coincidence is that 200mV is too small to turn-on Silicon junctions. While in-circuit readings are *always* dubious, Si junctions have little effect on reading.

[R.G.]

But my DMM reads forward resistance of silicon diodes on the resistance ranges. How does that work?

[PRR]

> How does that work?

Enlighten us, please?