Audio spectrum analyzer and power line. - Page 1
Forum section: electronics / projects

author: drm
author_rank: Contributor
timestamp: May 23, 2017, 06:34:16 pm
content: Dear ppl.I was wondering if i may use an audio spectrum analyzer software, that uses PC/notebookmicrophone input, to wacht the harmonics generated by a DC motor when it is being fedby a 220 vac power line via a triac triggered by phase angle modification.The pc-notebook mic input, will be acoupled with an inductor to the 220vac line.Will the 20khz bandwidth be enough to show the more annoying harmonics?

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 23, 2017, 06:46:16 pm
content: Define "annoying"? If you mean audible "hum" from the physical wiring, components, etc. Then the 20KHz limit may be useful. But then using a "jelly-bean" 82-cent electret mic capsule might prove as useful for "sniffing out" audible noise.OTOH, if by "annoying" you mean Radio-Frequency Interference (RFI), then it seems unlikely that using a method that limits you to a couple 10s of KHz would be very useful.There are lots of inexpensive Software-Defined Radio (SDR) USB "dongle" receivers out there which cover a very broad range of frequencies. The ~$20 products, however have a rather high lower-limit (25-30MHz) which would preclude much of the spectrum one might expect to find RFI from that sort of "offender". There are some more expensive SDR products that go down to 1MHz and that would seem useful.

author: rstofer
author_rank: Super Contributor
timestamp: May 23, 2017, 10:40:01 pm
content: Quote from: drm on May 23, 2017, 06:34:16 pmI have no idea what this means, perhaps a transformer? The idea of getting mains voltage anywhere near the sound system of a PC seems like a really bad idea.

author: Electro Detective
author_rank: Super Contributor
timestamp: May 24, 2017, 04:24:37 am
content: Quote from: rstofer on May 23, 2017, 10:40:01 pmSounds like a BBQ laptop affairbest avoided though I have been tempted myself to try it on a cheap laptop past its use by date.Might work if the laptop is FULLY isolated from the mains AND anything earth/grounded.Placed on a rubber mat or wood block etc and RUN ON INTERNAL BATTERY ONLY!Then you would need to reduce the 220 or 240 volt mains to mic or preferably line input levels with some sort of idiot proof (?!!) resistive network (?) in a FUSED box with 3.5mm breakout lead. What wire goes where on the TRS end I haven't decided on... yetYou could play it safe using step down isolation and audio transformers along the way, but that would defeat the purpose of seeing the raw mains as it is without the transformer influences on the signal.I am hoping EEVites hit on this ASAPand correct any stuff I've scratched on... that -no one should EVER try- at home

author: Someone
author_rank: Super Contributor
timestamp: May 24, 2017, 08:20:07 am
content: Quote from: Electro Detective on May 24, 2017, 04:24:37 amA small mains transformer will have a very practical bandwidth for doing measurements of power supply quality, carefully chosen it wont introduce any problematic distortion.

author: danadak
author_rank: Super Contributor
timestamp: May 24, 2017, 10:00:50 am
content: Here is a free application with scope and analyzer using sound card.https://www.zeitnitz.eu/scope_enPrevious comment on using transformer to couple to sounld card input, excellentapproach.Some methods of protecting sound card inputs -http://www.pmillett.com/ATEST.htmhttp://www.daqarta.com/dw_0all.htmhttp://www.electro-tech-online.com/threads/soundcard-oscilloscope-protection.92122/Regards, Dana.

author: The Soulman
author_rank: Super Contributor
timestamp: May 24, 2017, 10:58:29 am
content: I've been using zeitnitz's scope software for educational purposes for quite a while and its really great.To bad it's stuck at 16/44,1 because 24/192 with a decent (modified) sound card would be awesome.As mentioned before, hooking up something to mains without proper isolation would beat bestorworst case (you are the horse).Use a small transformer.

author: drm
author_rank: Contributor
timestamp: May 24, 2017, 06:32:24 pm
content: Ok ppl. thanks a lot to all the ones that have answered.I remembered that i had a current probe, that I used to wacht the collector current on the horizontaloutput stage of old trc tvs.It is designed to watch 15khzs signal, but do a decent work at low frequencies to start with.Heres what i got trying three different lamps.Incandescent, led and fluorescent at the end of thevideo.https://goo.gl/GhqYtdNow i am going to use the analyzer to verify the performance off differents kinds of filters, to reduce the EMI generated by the motor.

author: schmitt trigger
author_rank: Super Contributor
timestamp: May 24, 2017, 07:31:18 pm
content: Quote from: drm on May 23, 2017, 06:34:16 pmThe disturbances produced by such a circuit are current, and not voltage, harmonics.As such, you can safely measure the current utilizing one of the many hall-cell based sensors, like the ubiquitous ACS7xx series from Allegro.That way, you achieve both isolation and scaling in a simple to use device.