Home DIY Electronics

G Meier's Comment

Wed, 12 Jun 2024 19:05:06 +0100

I measured on a transformator, 230V AC, the voltage on the second winding, 30V AC, but
my soundcard oscilloskop showed a SQUARE output! No SINUS-wave... I expected
a sinus wave of cause. The square wave was not fifty fifty. Duty about 70% on
and 30% off. What the hell...

DANIEL JACKSON's Comment

Sun, 08 Mar 2020 16:14:25 +0000

can i use this for repair of two way radios like CB's for example? either on laptop or minitowers or towers??

Steve's Comment

Tue, 17 Feb 2015 12:33:26 +0000

Hi Mike,

I've just tried it on my Windows 8.1 PC and it appears to be fine. Make sure that the Run/Stop button is green and the Amplitude knob is turned anti-clockwise to increase the gain. Also remember that the sound card scope cannot display DC.

Hope this helps.
Steve

mike's Comment

Tue, 17 Feb 2015 10:50:25 +0000

I have this running on Win 8.1 but it works only for about 1 second when I put a signal on the I/P and then it drops to a straight line.

Steve's Comment

Wed, 24 Dec 2014 18:33:40 +0000

Hi Mughees,

There could be a number of reasons for your problem.

First of all the PC sound card is AC coupled so it is not possible to display a DC level. This doesn't sound like your problem however.

Have you tried applying an ac signal to the scope? If you have and all you get is noise then there is either a wiring problem with your probe or the mic input has not been selected as audio input on your PC. This is assuming that your sound card is ok of course. You should check this by trying another application that uses the mic input.

If your wiring is all good then I suggest you make sure that the audio input mixer on your PC is set to use the mic as input.

Steve

Mughees's Comment

Wed, 24 Dec 2014 10:32:23 +0000

Hello Steve,
I am facing a problem. I am applying the dc to scope but it only displays noise instead of showing a straight dc line !!! plz help me in resolving this

Marut's Comment

Mon, 11 Aug 2014 18:41:18 +0100

Thank you so much Steve. Precisely what I wanted...

Steve's Comment

Sun, 10 Aug 2014 15:16:11 +0100

Hi Marut,

The simple answer is do not apply peak to peak voltages of more than 1V.

The long answer is more complicated. The microphone input is designed to work with signals of only 10mV. If you have a line input or a dual line/microphone input then the specification is usually 100mV. So to be fully certain of not damaging your sound card without knowing exactly what the specification of your card is, you should stick with signals with amplitude less than this.

Most signals that you work with are likely to have greater amplitude than the card will accommodate so the sound card oscilloscope probe circuit is designed to attenuate the signal as well as protect the PC audio input circuitry. The circuit in the book is designed to work with signals up to 30 V peak to peak.

The other problem you will encounter if you apply larger signals is that the sound card will start to clip. A sign wave will look flat at top and bottom indicating severe distortion. This will likely happen before any damage occurs.

I have never tested any sound card to it's limits because I don't have a sacrificial PC. Doing so would not be of much value because my intention is that the sound card oscilloscope circuit should work with all sound cards some of which may have lower input specifications than others.

I have tested several PCs with inputs of up to 1.2 V peak to peak with no damage and no clipping so this is probably a save level for most sound cards. Please do not try applying larger signals unless you don't mind damaging the card.

I hope this helps.

Steve

Marut's Comment

Sat, 09 Aug 2014 14:56:20 +0100

Steve I need help.

Suppose I am directly giving the input to the soundcard without the protection circuit, what is the maximum voltage that I can allow to pass without blowing up my soundcard?

Specifically, would voltages less than 9V range be safe to pass directly?