Hooking up iPhone audio output to a scope? - Page 1
Forum section: electronics / beginners

author: elroy
author_rank: Regular Contributor
timestamp: October 28, 2017, 04:37:54 pm
content: I just bought my first oscilloscope, a Siglent SDS1202X-E, and have been reading up, watching videos and trying a few experiments to get to know it better.One thing I was interested in trying would be to put the scope in XY mode, then connect the horizontal and vertical inputs to the left and right channels of stereo audio to see what kind of patterns it produces. I was thinking I might do this by connecting the scope probes (via a 3.5mm plug and dissected cable) to the headphone jack of an iPhone playing music.This seems as though it ought to be safe, but I thought just to be sure I ought to ask. Is there anything I need to worry about?

author: ahbushnell
author_rank: Frequent Contributor
timestamp: October 28, 2017, 05:03:16 pm
content: Should be fine. Just don't short the output of your phone.

author: elroy
author_rank: Regular Contributor
timestamp: October 28, 2017, 06:01:08 pm
content: Quote from: ahbushnell on October 28, 2017, 05:03:16 pmThanks. I gather the issue if that were to happen would be with the phone, not the scope?

author: ElectronicCat
author_rank: Regular Contributor
timestamp: October 28, 2017, 08:07:15 pm
content: Yes, should be safe. The phone can't provide any kind of power that would be damaging to the scope. Only possible danger would be shorting out the headphone jack, but even then I suspect the phone has protection for that as it is likely to be shorted when plugging in a headphone cable.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: October 28, 2017, 08:25:20 pm
content: Quote from: elroy on October 28, 2017, 06:01:08 pmYes could be hard on the phone.Sent from my SM-G930V using Tapatalk

author: 3db
author_rank: Frequent Contributor
timestamp: October 28, 2017, 11:31:02 pm
content: Might be a good idea to leave the phone charger disconnected from the phone too.

author: elroy
author_rank: Regular Contributor
timestamp: October 28, 2017, 11:43:36 pm
content: Thanks for all the suggestions. Seemed to work out okay.

author: Audioguru
author_rank: Super Contributor
timestamp: October 29, 2017, 12:11:07 am
content: Your scope shows only one channel with a normal timebase.In XY mode one channel is for vertical and the other channel is for horizontal then mono produces a diagonal line and stereo music produces a changing tangle of thread. The size of the tangle is the signal level. No signal produces a dot in the center.

author: elroy
author_rank: Regular Contributor
timestamp: October 29, 2017, 12:56:23 am
content: Quote from: Audioguru on October 29, 2017, 12:11:07 amGood point -- I thought the waveform wasn't what I expected. I tried again, and this time I think I got it into XY mode correctly. Though the display still may need more tweaking.

author: BMack
author_rank: Regular Contributor
timestamp: October 29, 2017, 05:31:36 am
content: BTW, for trouble shooting audio equipment on the cheap the iPhone makes a decent signal generator with an app. All you need is the phone, a 3.5 to RCA cable and two RCA to BNC adapters...and scope obviously. I've tested it and it easily handles up to 10k(it started getting noisy in the 22K range or so) spot on with the app I have on the phone. I barely use it but it's a nice option when you have a larger audio piece and you pair with a scopemeter.

author: Frank O
author_rank: Newbie
timestamp: October 29, 2017, 05:44:25 am
content: Quote from: BMack on October 29, 2017, 05:31:36 amInteresting. What app are you using on the phone?

author: alsetalokin4017
author_rank: Super Contributor
timestamp: October 29, 2017, 07:58:51 am
content: Look for the "oscillofun" sound file and see if you can get a good display of that.Also check out Jerobeam Fenderson....

author: tooki
author_rank: Super Contributor
timestamp: October 30, 2017, 01:55:09 am
content: Quote from: Frank O on October 29, 2017, 05:44:25 amI use this on iPhone and iPad for my audio projects: “Audio Signal Generator including Sweeps & Noise by Thomas Gruber”https://itunes.apple.com/us/app/audio-signal-generator-including-sweeps-noise/id768229610?mt=8Don’t worry about shorting out the output - it won’t kill anything. (I have yet to see a headphone amp chip that isn’t short-circuit safe.) It may, however, confuse the playback controls, depending on whether and when the microphone pin gets shorted to ground, too. (That’s fundamentally how the play/pause button works.) You could always build a little NE5532 buffer amp to use in the middle.

author: BMack
author_rank: Regular Contributor
timestamp: October 30, 2017, 05:14:26 am
content: Quote from: Frank O on October 29, 2017, 05:44:25 amI think it's called Tone generator. I literally downloaded the first one, then tested it before using it. No square wave or anything fancy but it's simple and free. I was extremely impressed with what I could get out of it, all I needed was 3k but I kept pushing it and it vastly exceeded my expectations.