On 6/20/07, Andre Abelian wrote: > Mark, > > thanks for your info. In my case I already know what the problem is > but I want to mask it because of there is no way I can convince the > guy here to use 10bit ADC instead of 13 bit. I already check with > sensor makers they do not recommend ADC higher then 10 bit but > no thing I can do. The extra noise comes from the sensor > > Andre > That was Rich who provided information, not me. I just asked a question. There is no problem using extra bits in the ADC than you need. For example, you could ignore the the lowest 3 bits (set them to zero) and then you would have the equivalent of a 10-bit ADC. Anti-aliasing is a bigger subject than I want to tackle in an email message, especially since there are good explanations on the web. In a nutshell, if you sample at 100 Hz, and there is information in the analog signal at frequencies above 50 Hz, that information will show up in the sampled representation at a lower frequency. No amount of software filtering can fix the problem. You must low-pass filter the incoming data at half the sample rate (or less). Google for "ADC anti-aliasing" or "Nyquist frequency" to learn more. Regards, Mark markrages@gmail -- Mark Rages, Engineer Midwest Telecine LLC markrages@midwesttelecine.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist