hooking oscilloscope to PC aaudio - Page 1
Forum section: electronics / testgear

author: cyberwasp
author_rank: Contributor
timestamp: February 05, 2020, 05:51:03 pm
content: I wonder if someone could advise me how to safely hook a desktop PC's audio output to an Oscilloscope. I watched an EEVblog titled, "how not to blow up your oscilloscope," and I don't want to risk it as I recently purchased a new, "for me," SDS1202X-E and don't want to kill it so I've been sticking to Arduino projects. TIA

author: james_s
author_rank: Super Contributor
timestamp: February 05, 2020, 05:59:36 pm
content: Any IO on a PC will be safely isolated from line voltage so you can poke at any of it with your scope without worries. As long as you stay outside of the power supply that plugs into the wall you will be fine.

author: tautech
author_rank: Super Contributor
timestamp: February 05, 2020, 07:50:40 pm
content: Quote from: cyberwasp on February 05, 2020, 05:51:03 pmJust apply a simple rule; if circuit ground = scope ground you can connect the probe reference (ground) clip most anywhere onto the DUT ground.If unsure use your DMM to measure any possible potential difference.Get into the habit of using probes always set to 10x and set the scope inputs to the same so scope measurements won't be wrong by a factor of 10. Probes set to 10x load the DUT much less than 1x however for low impedance test points the additional capacitance of 1x is of little concern.Stay safe and have fun with your new DSO.

author: magic
author_rank: Super Contributor
timestamp: February 05, 2020, 09:46:46 pm
content: Quote from: james_s on February 05, 2020, 05:59:36 pmYou can poke anywhere you want with the probe. The grounding clip has to go to ground, anything else is not going to work and may blow up the scope or the PC.

author: james_s
author_rank: Super Contributor
timestamp: February 05, 2020, 09:51:25 pm
content: That's not entirely true, you can easily blow up a scope by poking at voltages higher than it is able to safely handle.You won't find any such things on the outside of a PC though.

author: magic
author_rank: Super Contributor
timestamp: February 05, 2020, 09:53:15 pm
content: I expanded on your answer, so by "anywhere", I meant "anywhere near the PC except for the guts of its PSU"

author: vk6zgo
author_rank: Super Contributor
timestamp: February 06, 2020, 02:21:11 am
content: The PC maker has no control over what devices may be plugged into the audio output, so takes the sensible precaution of not having any voltages on it, other than the audio output signal.If you put your probe on "backwards" (with the "ground clip" on the non -grounded output), the most likely outcome is that you won't see anything.*With a desktop, it will probably short circuit the audio amplifier output, but it will most probably survive this OK, although you shouldn't make a habit of it!Again, with a desktop, you can probably tell which wire is which by not connecting your ground clip at all to the wires, but pick up a point of the back of the PC where there are often metal panels, or connectors with metal outer shells, & connect it there.*A laptop will normally not have a direct ground connection, but it depends on whether you have any other devices connected to it.Hams plug stuff into the audio inputs & outputs of their PCs all the time when they want to use the various "digital modes" in their transmission & reception, with very few problems.

author: cyberwasp
author_rank: Contributor
timestamp: February 06, 2020, 04:00:14 am
content: Wow , alot of information. Right now the only thing connected is a mouse, keyboard and Ethernet. as for sound I just have a Ankor blue tooth speaker hard wired to the pc's audio jack. My thought was pull the plug out of the ankor and connect the scope to the audio plug.Now I do have an Micsig DP10013 High Voltage Differential Probe, would it be better to use that?Sorry guys, am a total beginner here and want to be safe! Thank you all!

author: james_s
author_rank: Super Contributor
timestamp: February 06, 2020, 06:18:11 pm
content: You don't need a HV differential probe for this, and really if you are a total beginner you shouldn't be doing anything that needs one of those at all.As I've already said, as long as you don't open up the power supply and start poking around in there, there is nothing coming out of a PC that will harm your scope, it's all low voltage, probe around all you like. The audio jack is perfectly safe, it's not going to hurt the scope and the scope is not going to hurt it.

author: cyberwasp
author_rank: Contributor
timestamp: February 07, 2020, 02:49:56 am
content: Quote from: james_s on February 06, 2020, 06:18:11 pmThank you James. I sent for a y 3.5mm stereo adapter so I can keep the speaker connect while I attach the scope!