Post by thread:Noise in audio circuit

<x-flowed>I'm working on a project that uses an ISD2560 sound recorder with an SX as the controller. The circuit is working but there is background noise generated by oscillations that occur when I read 2 pots that control the frequency of the playback. If I add delays between the code that reads the pot I get a lower pitch but I can't get it to go away completely without making the response time to slow. I tried putting filter caps of different sizes but no success. Any suggestions would be great, I'm a software guy and this hardware stuff kills me sometimes. Thanks Bill ________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com </x-flowed>

Bill, Is there any way to rewrite the POT READING ROUTINE to sample at a faster rate, and thus move the noise to higher than hearing range? Regards, Jim On Wed, 03 May 2000, Bill Pierce wrote: {Quote hidden}> > I'm working on a project that uses an ISD2560 sound recorder with an SX as > the controller. The circuit is working but there is background noise > generated by oscillations that occur when I read 2 pots that control the > frequency of the playback. If I add delays between the code that reads the > pot I get a lower pitch but I can't get it to go away completely without > making the response time to slow. I tried putting filter caps of different > sizes but no success. Any suggestions would be great, I'm a software guy and > this hardware stuff kills me sometimes. > > Thanks > > Bill > ________________________________________________________________________ > Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com spam_OUTjimTakeThisOuTjpes.com

How do those oscillations occur, is the thing I'm curious about at this point? Instead of trying to stifle the effects, sometimes it's far easier to solve the problem by solving it's cause. You do have decoupling caps (say 10uF and 0.1uF in parallel) on the Vss/Vdd at both the ISD2560 and the SX, right? And perhaps a small series resistor inline with the SX's Vdd, to reduce coupling of digital noise to the ISD? One-point grounding between the two, as well? Mark Bill Pierce wrote: {Quote hidden}> I'm working on a project that uses an ISD2560 sound recorder with an SX as > the controller. The circuit is working but there is background noise > generated by oscillations that occur when I read 2 pots that control the > frequency of the playback. If I add delays between the code that reads the > pot I get a lower pitch but I can't get it to go away completely without > making the response time to slow. I tried putting filter caps of different > sizes but no success. Any suggestions would be great, I'm a software guy and > this hardware stuff kills me sometimes. > > Thanks > > Bill > ________________________________________________________________________ > Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com -- I re-ship for small US & overseas businesses, world-wide. (For private individuals at cost; ask.)

<x-flowed>I have 10uf and 0.1uf in parallel at the regulator but not at both the SX and the ISD2560. I'll try that as well as the resistor tonite. The oscillations happen becuase I am reading the pots at a pretty high frequency and each time the pot is read the pin goes from high to low in a nice curve because the cap is discharging. I'm not sure if changing the pin from input to output is helping either. I did try lowering the frequency that I read the pot and the noise did lower in frequency as expected but did not go away. Now I just have a very low hum instead of a high pitched noise. Its kinda cool to play with both pots and change the frequency to play tunes. Unfortunately I don't think that my customers would like that too much. Thanks Bill {Quote hidden}>From: Mark Willis <.....mwillisKILLspam@spam@FOXINTERNET.NET> >Reply-To: pic microcontroller discussion list <PICLISTKILLspamMITVMA.MIT.EDU> >To: .....PICLISTKILLspam.....MITVMA.MIT.EDU >Subject: Re: Noise in audio circuit >Date: Wed, 3 May 2000 13:51:11 -0700 > >How do those oscillations occur, is the thing I'm curious about at this >point? Instead of trying to stifle the effects, sometimes it's far >easier to solve the problem by solving it's cause. > >You do have decoupling caps (say 10uF and 0.1uF in parallel) on the >Vss/Vdd at both the ISD2560 and the SX, right? And perhaps a small >series resistor inline with the SX's Vdd, to reduce coupling of digital >noise to the ISD? One-point grounding between the two, as well? > > Mark > >Bill Pierce wrote: > > I'm working on a project that uses an ISD2560 sound recorder with an SX >as > > the controller. The circuit is working but there is background noise > > generated by oscillations that occur when I read 2 pots that control the > > frequency of the playback. If I add delays between the code that reads >the > > pot I get a lower pitch but I can't get it to go away completely without > > making the response time to slow. I tried putting filter caps of >different > > sizes but no success. Any suggestions would be great, I'm a software guy >and > > this hardware stuff kills me sometimes. > > > > Thanks > > > > Bill > > ________________________________________________________________________ > > Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com > >-- >I re-ship for small US & overseas businesses, world-wide. >(For private individuals at cost; ask.) ________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com </x-flowed>

> I have 10uf and 0.1uf in parallel at the regulator but not at both the SX > and the ISD2560. I'll try that as well as the resistor tonite. The > oscillations happen becuase I am reading the pots at a pretty high frequency > and each time the pot is read the pin goes from high to low in a nice curve > because the cap is discharging. I'm not sure if changing the pin from input > to output is helping either. > The resistance of the pots/source is too high for the a/d input. The best way is really to buffer the analog with an opamp where the output goes to the A/D and wires back to the inverting input. If this is not an option try a lower value pot and/or a cap on the wiper to A/D wire, say 100nF. This may help stop the sagging/oscillations but could be a problem if this pin is shared with an output. I have sometimes used 1uF caps to stop sag from a relatively high impedence, very application dependent though. _____________________________ Lance Allen Technical Officer Uni of Auckland Psych Dept New Zealand http://www.psych.auckland.ac.nz _____________________________