# need to measure low freq. DC waveform

M

#### [email protected]

Jan 1, 1970
0
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?

M

#### Max65

Jan 1, 1970
0
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

U

#### [email protected]

Jan 1, 1970
0
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

C

#### CJT

Jan 1, 1970
0
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.

M

#### Max65

Jan 1, 1970
0
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
Massimo

M
Replies
8
Views
1K
Phil Allison
P
J
Replies
8
Views
2K
Baphomet
B
Replies
13
Views
2K
Replies
6
Views
1K
Replies
2
Views
8K