Smart phone as an audio signal generator. - Page 1
Forum section: electronics / testgear

author: elcomtel
author_rank: Regular Contributor
timestamp: August 08, 2013, 02:55:18 pm
content: Nothing very exciting about this post and most of you probably already have tried this, but for the benefit of some of the aspiring electronics novices out there I thought they might be interested that they carry a piece of test equipment with them.I was working on a customer site and it very quickly became apparent that I needed an audio signal generator for the job at hand. Being a quite a resourceful sort of fellow, I followed my instincts and suspected my Android phone could be used as a signal generator.A quick visit to Google Play (http://play.google.com/) and a search using the parameters "signal" and "generator" revealed a plethora of "audio signal generator" applications.Very shortly afterwards I had a good range of adjustable audio test signals to diagnose and test my customers audio system.

author: saturation
author_rank: Super Contributor
timestamp: August 08, 2013, 06:42:59 pm
content: Thanks for the tip. On your lead I took one with a decent technical review, FuncGen.Checked it on the Rigol 1052e also with FFT. The good news is the sine waves are flat ~ 20Hz-17kHz and the frequency is stable, it drops quickly thereafter to 20kHz. Some waveforms generate small spurs 3-4x the fundamental about - 30dB.The default triangle wave distorts above 1kHz and the square has a lot of ringing too. All the other functions work with the above limitations and within the constraints of the menu items [ e.g. sweep rate or modulation %].Nevertheless, it can be recommendedas a pocket signal generator for gross testing whenever you need an audio signal such as troubleshooting speakers, headphones or testing gross frequency response. The menu system is workable but crude, no bugs immediately noticeable.Generated using a Droid 2 on a 100 ohm resistive load to emulate headphones.

author: brainwash
author_rank: Frequent Contributor
timestamp: August 09, 2013, 02:13:20 am
content: And guess what? It's also an oscilloscope!Most of them at 16Ksps, some of them 44Ksps, but still better than nothing.

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: August 09, 2013, 12:28:50 pm
content: I have both Apple and Android products and have found that these apps really depend on the hardware for decent to good performance. The iPad seems to have very good audio waveform performance where my Galaxy S3 has average performance.

author: Sigmoid
author_rank: Frequent Contributor
timestamp: August 09, 2013, 02:17:44 pm
content: Hm...A technical question!What kind of output coupling should I build in order to use the audio output from a smartphone without fear of frying the device?Can someone help me with the selection of DC decoupling caps - where should I put the cutoff point of the filter? Also, I've got the feeling I cannot really use electrolytics, as I haven't the slightest idea of the direction of the DC bias when it's driving something live...Are tantalums a good idea?EDIT yea tantalums are electrolytics and will burn when given back voltage. XD The question still stands for large nonpolarized ones, like big ceramics.Do those also need a smaller cap in parallel to counteract the internal inductance, or is it only for electrolytics?Also usually what is the output impedance of a function generator?

author: saturation
author_rank: Super Contributor
timestamp: August 09, 2013, 08:06:26 pm
content: Yes, 2 key problems I see are while a signal generator feeds data out, a scope takes data in; second its mandatory to use a hardware adapter for a scope application so there is some financial expense; if the hardware were not designed right or its used inappropriately you can damage your phone or even yourself; for $50-100 for a scope adapter you maybe better off getting the DSO nano, FWIW.Quote from: brainwash on August 09, 2013, 02:13:20 amYes, I'd anticipate given the hardware is different, you can expect different results from different phone models as well as apps themselves. Best to test each individually.Quote from: Terabyte2007 on August 09, 2013, 12:28:50 pmI'd isolate the output using an isolation transformer or a ground loop isolator. I'd buffer the secondary stage with a op amp rigged as a voltage follower. Add switchable series resistor 50 ohms to emulate a function generator, 110 ohms for headphones, 16 ohms for speakers etc.,Quote from: Sigmoid on August 09, 2013, 02:17:44 pm

author: Bored@Work
author_rank: Super Contributor
timestamp: August 09, 2013, 08:26:17 pm
content: Quote from: Sigmoid on August 09, 2013, 02:17:44 pmA 10 cm (4 inch) air gap.

author: Sigmoid
author_rank: Frequent Contributor
timestamp: August 10, 2013, 12:15:08 am
content: Quote from: Bored@Work on August 09, 2013, 08:26:17 pmLOL! XD

author: beun
author_rank: Newbie
timestamp: February 10, 2014, 09:12:43 pm
content: I know I am a bit late responding to this thread, I am the developer of the FuncGen signal generator for Android. A few observations:1) As mentioned by others, the quality of the output solely depends on the phone hardware, the code itself is essentially perfect with full 16bit accuracy2) Per default the triangle and square wave are anti aliased, this looks like distortion and ringing but is actually the Gibbs phenomenon. If you don't want to see the ringing but don't mind additional spurious you can switch of the anti aliasing function. Unfortunately you can't have both at the same time.