need to measure low freq. DC waveform

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?

 

[Max65]

On 18 Mag, 09:06, mattyg1...@hotmail.com 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?

you could use your sound card chopping the incoming signal with a
fixed frequency of 10kHz or so, by means of a cmos switch such as the
CD4066 (if you need precision, it is better you use one DG411 or one
next generation switches with lower RDon resistance).
To achieve a good switched signal place one switch in series and one
in parallel to the sound card input, and drive the second one with the
logic complement of the first.
Bye,
Massimo

 

mattyg1884@hotmail.com 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. CHEAP enough ?

Yukio YANO

 

[CJT]

mattyg1884@hotmail.com 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?

What you want is a DVM.

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The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.

 

[Max65]

On 21 Mag, 03:08, u...@domain.invalid wrote:

mattyg1...@hotmail.com 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.  CHEAP 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