On 10 November 2011 13:17, doug metzler wrote: > what powers it? > > DougM > > > On Wed, Nov 9, 2011 at 3:11 PM, Yigit Turgut wrote: >> I had experienced a variant of this audible sound at a distribution >> facility (~380kV) but I wouldn't guess that it would be observable in >> a circuit like this. There are PIC's, resistors, electrolyte caps and >> xtals. I believe it won't hurt to operate like this but it is obvious >> that this noise is a waste of energy. >> >> On Wed, Nov 9, 2011 at 8:28 PM, Sean Breheny wrote: >>> Inductors are the most common noise source, but ceramic capacitors, >>> especially ones with high dielectric constant dielectrics (not NP0/C0G >>> types), can also make noise if the voltage across them is changing >>> significantly. >>> >>> On Wed, Nov 9, 2011 at 12:40 PM, Herbert Graf wrote: >>>> On Wed, 2011-11-09 at 19:30 +0200, Yigit Turgut wrote: >>>>> Hi all, >>>>> >>>>> I have a product and everything works as expected except one thing ; >>>>> there is a hiss/noise coming from the circuit (not the speakers, >>>>> actual circuit). I recorded and analyzed the sound, it is an >>>>> approximately 2khz signal (clock is 48mhz) but not sure which >>>>> component it is originating from. My first guess was it could be a >>>>> capacitor because there aren't many analog components on the board bu= t >>>>> it could be another one as well. >>>>> >>>>> Has anyone encountered such a behavior ? >>>> >>>> Certainly. Many power supplies have an audible sound. Most common thin= gs >>>> that generate sound are windings. Inductors, transformers and chokes a= re >>>> the biggest ones. Do you have any of those on your board? >>>> >>>> Thanks, TTYL >>>> >>>> -- >>>> http://www.piclist.com PIC/SX FAQ & list archive >>>> View/change your membership options at >>>> http://mailman.mit.edu/mailman/listinfo/piclist >>>> Yigit, We recently had a similar problem with a microphone on a PDA type device picking up an audible tone. It turned out to be a ceramic capacitor on the backlight suppy. Changing the cap to a film type fixed the problem. So inductors are not the only possible cause - although it was where we looked first. IIRC I tracked it down using a microphone on a length of flexible cable feeding a PC & soundcard running some sort of FFT software. The mic was small enough to move close to suspect components and the source was localised pretty quickly. The FFT software made the noise a lot more "visible" than a simple scope tr= ace. RP --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .