Using LM231 Voltage-to-Frequency Converter to Record Analog Data as Audio Tone?

Hi,

I'm trying to record analog values with a digital recorder. Basically I have a recorder and have 2 leads connected via the mic port. If I just apply regular voltage to the leads the recorder doesn't recognize the external mic and records with the internal mic. It seems as though the recorder will only read values through the external mic if there is a tone going through it. I know the Arduino can generate tones, but if possible I'd like to do this with a simple voltage to frequency converter IC like the Texas Instruments LM231 (http://www.ti.com/lit/ds/symlink/lm231.pdf). My question is: if I convert voltage to frequency, is that the *same* thing as generating a tone (will it be readable)?

Thanks!

If you convert v to f then you are generating an alternating waveform which if the frequency is within the audible range, normally 30hz up to 18khz then yes you are generating a tone

If the voltage is fixed or at a constant dc level then the frequency of the wave produced by that voltage, or in your case the v to f convertor will also be fixed

So you are producing a stabel unchanged frequency which is not varying

You might in one context describe this as a musical note or a tone I.e if you were to view this on a scope then the period and the amplitude would be constant as long as your voltage input was constant

Here is an oscilloscope software package that you can use for checking your waveforms Dont use this with raw mains as input Read instructions carefully before using

OR

You can try this address for other scope software
www.zeitnitz.de/Cristian/Scope/Scope_en.html
Thats if the link is still active

If you are trying to see DC or low frequency voltages then the input device probably filters then out. A V to F converter usually produces a square wave which may not be in the audible range, or may be near the edges of the vrange so it will be affected by the input filtering, possibly in interesting ways.

A square wave can be considered a sin wave of the same frequency added to every odd harmonic. If you draw a sine wave along with a sine wave at three times the frequency and five times and add them graphically you'll see a rough square wave.

As to reading it, it depends on what you use to read it. Recorders for audio signals often have band width limitations and filters so they ignore signals outside the normal autio range, which can be 50Hz to 20 KHz.. Since a square wave is made up of odd harmonics, a 20 Hz square wave may have its lower harmonics filtered and appear as a weaker 40 or 60 Hz signal.

I have a digital recorder (Sony IC Recorder ICD-UX70) and when I plug something into the external mic, the recorder detects it and "asks" me if I want to "Select Input: Mic In or Audio In" By "Mic In" it means the internal mic and by "Audio In" it is referring to the jack.

I'm not sure how it is detecting the act of plugging, but I suspect it does a continuity check on the "ring" part of the plug, but, perhaps it's by some other means, such as listening for audio signal on the external input (not how I would do it, because there might not always be a signal to detect).

But, it makes me wonder if applying a DC voltage (what I assume you mean by "regular voltage") to the external input, as you say you are doing, doesn't, some how, mess with that detection process and thus cause the affects you are seeing.

A continuity check might make sense but a continuity check on just the ring is like one hand clapping. There are switches built into many jacks that might do this. Maybe the switches are in series to save money or inputs?

Sometimes the ring and tip are shorted when nothing's plugged in. This might be detected though I can't see why the computer wouldn't know which signal was no longer shorted. Maybe it's just bad software. If it's Microsoft I'd expect it.

Any sort of filter that limits the bandwidth would completely strip off any DC signal.