Help with USB sound card oscilloscope - Page 1
Forum section: electronics / projects

author: sevenofnine33
author_rank: Contributor
timestamp: April 19, 2018, 07:02:07 pm
content: Hello, I just bought a USB sound card and was hoping to make it into an oscilloscope. The problem is I'm not sure how I'm supposed to do it. Projects I found online were not clear to me, can anybody help?http://www.instructables.com/id/USB-Oscilloscope-with-Signal-generator/Is this a good project?

author: JS
author_rank: Frequent Contributor
timestamp: April 19, 2018, 09:25:41 pm
content: That project is quite limited, doesn't provide much protection to the soundcard or the PC it's connected to. Depending on what you plan to meassure might be enough, let's say you want to test small audio projects running on 9V batteries, that's ok. Mains connected SMPS not ok.I don't know what project is good for this, it will always be a very limited tool, but I'd try to get a buffered amp, high impedance (1M would be optimal as standard 10X proves would work with it and they are cheap) and input should be protected somehow, some series resistance and reasonable clamping would be a first step. With a soundcard you will always have AC coupled input so might be a good idea to make the input of your circuit also AC coupled as you won't know if you are clipping due to DC offset in the input or the signal is just like that.Also you might want to have switchable gain, 0.1, 0.2, 0.5, 1, 2 ,5 and 10 would be a nice start.For the signal generator you might also want to have a buffer, standard is 50? output but sometimes for audio is good to have a low impedance output (an opamp, maybe driving some extra transistors, directly to the output) and then your switchable 50? resistor. Also here would be good to have a few selectableThis config would be a good starting point I guess, just 4 opamps, a few zenners to provide clamping and some passives, switches and connectors. At all time using it (and before getting into the project) you should have in mind that the thing would only work from 20HZ-ish (maybe less depending on the soundcard) to 20kHz-ish depending on the sampling frequency. I've done 90kHz-ish measurements with my sound card, but mostly testing analog audio stuff which doesn't need any special connection to the soundcard. I don't remember using it as an osciloscope for other than that, and even then more than an osciloscope an audio test setup. I did use some low impedance output buffers when testing some stuff.JS

author: sevenofnine33
author_rank: Contributor
timestamp: May 02, 2018, 06:23:48 pm
content: I need it to measure signals from my Arduino projects, so I don't need it to capture big voltages.Also, I am a beginner, so if you have the time to draw the schematic for the project I would very much appreciate it.Best regards.

author: wholder
author_rank: Regular Contributor
timestamp: May 02, 2018, 11:07:59 pm
content: The circuit shown in the article you linked should work fine, as it's a simple resistive divider. But, of course, I'll repeat the warning about the need to be careful or you could damage your computer.Wayne

author: ledtester
author_rank: Super Contributor
timestamp: May 03, 2018, 04:25:34 pm
content: Just wanted to add that this site contains a lot of useful software for sound card based instruments:http://www.daqarta.com/Update: Ok - just realized it's not totally free software, but still might be worth investigating.

author: ledtester
author_rank: Super Contributor
timestamp: May 03, 2018, 04:51:23 pm
content: To give yourself a little input protection, have a look at this article:https://makezine.com/projects/sound-card-oscilloscope/This circuit uses a pot instead of fixed resistors to attenuate the input signal. It also adds clamping diodes in case the input signal is too large for the sound card.

author: SiliconWizard
author_rank: Super Contributor
timestamp: May 03, 2018, 05:16:21 pm
content: As said above, don't forget to properly protect your inputs. You could fry your sound card or even worse, your computer.Unless it's just for fun, or you only want to deal with audio signals (in which case a good sound card would be WAY better than an oscilloscope), I would strongly suggest investing in a small oscilloscope instead, though.For instance, you can get an Hantek 2 channels/20Mhz USB scope for like $70-$80. Those are properly protected and will allow you to do much more.