On Wed, 22 Sep 1999 20:31:42 -0400 Mario Thomaidis writes: >Whoa ... reset. I had thought I had not considered Harold's point >below, >but I previously had (honest!). Even if one is not going to be >reconstructing the original signal from its associated samples, one >should still include a low pass filter if only to help limit noise >which >might enter the system. > You can spend the money on one or more LPF's if you wish. If the LPF is after the mux, you'll have to delay before doing the A/D to allow for the LPF settling time. If you put the LPF before the mux (requiring a lot of them), the settling is done before the mux even gets to that channel. I have three products in production that read 10K pots thru 4051's into 16c74b chips. No LPF is included. It is very difficult to set the pots so the numbers out of the A/D dither, so the noise is much less than 0.5 lsb. Comparing this with other designs that have A/D noise, I believe the lack of noise on these designs is due to the use of a solid ground plane (both sides of the board, except where there are traces, pads, or vias), wide (50 mils) +5V traces, and bypassing at each chip with 220nF. Again, you can spend the money on LPF's, but, in my opinion, they are not necessary when you are just reading pot positions. Harold Harold Hallikainen harold@hallikainen.com Hallikainen & Friends, Inc. See the FCC Rules at http://hallikainen.com/FccRules and comments filed in LPFM proceeding at http://hallikainen.com/lpfm ___________________________________________________________________ Get the Internet just the way you want it. Free software, free e-mail, and free Internet access for a month! Try Juno Web: http://dl.www.juno.com/dynoget/tagj.