Re: need to measure low freq. DC waveform

On 21 Mag, 03:08, u...@[EMAIL PROTECTED]
 wrote:
> mattyg1...@[EMAIL PROTECTED]
 wrote:
> > i need to measure a low frequency waveform from a DC circuit (voltage
> > up to 200mV). I need a sample rate of around 10Hz. to buy an
> > oscilloscope for this is a total overkill. I was thinking of using the
> > soundcard, but then realised it's AC coupled. any suggestions on a
> > cheap method to find this measurement?
>
> A Voltage to Frequency converter can be as simple as a UJT oscillator
> IE about 3/4 resistors 2/3 Caps a UJT and a battery or a 555 IC and some
> electronic glue. =A0CHEAP enough ?
>
> Yukio YANO

I didn't mean to built a voltage to frequency converter (if you want
to do it you can use the LM331 that's very linear). I meant to
superimpose to the input signal a frequency to allow the sound card to
measure its peak to peak value which will be the value of the DC
signal. This method was used in early networks analyzers to void the
input amplifiers offsets without more complex temperature compensation
circuitry.
I don't believe he need a simple DVM, maybe it could be enough a
logging DVM instead.
Massimo