Quoting John Ferrell : > I have tried that circuit without the "BFTranzorb" and the 2k resistor with > the same noisy results. *With* that value electrolytic capacitor mounted close to the MCU, and directly between analog ground and the analog input? > I guess I live a sheltered life, this was the first time I had heard the > word "Tranzorb" Perhaps better known by the generic term "TVS". The BF, of course, is "Big Fat". > John Ferrell W8CCW > > "All that is necessary for the triumph of evil is for good men to do > nothing." -- Edmund Burke > http://DixieNC.US > > ----- Original Message ----- > From: "Spehro Pefhany" > To: > Sent: Wednesday, May 07, 2008 11:58 AM > Subject: Re: [PIC]Analog signal conditioning > > >> Quoting "M. Adam Davis" : >> >>> Something you might try is measuring using current from the shack >>> side. Set up a constant current source (LM317 or similar) and then >>> measure the voltage at the output of the regulator. The voltage will >>> vary based on the position of the pot in order to make the current >>> constant. >>> >>> It should help significantly, based on the description of the problems >>> you're having. >>> >>> -Adam >> >> >> >> >> Vdd >> +----------+ >> .-. >> | | 499R >> | | >> '-' >> | >> +------------+--------------------------------+----+ >> | | | >> \ | | .-. | >> - | 500R Pot | |<--+ >> BFTranzorb ^ \ | | | >> eg. 10V | | '-' >> | | | >> +---------+----------- | -------------------------------+ >> | | >> === | >> GND | >> | >> | >> | >> | >> | To ANx PIC >> .-. +------+---------------+ >> 2K | | | | + >> | | | --- >> '-' | --- 47uF/16V >> | | | >> +------+ | >> === >> GND >> >> >> The voltage at the ADC input is >> >> V = Rx/(499 + Rx) so it varies from 0 to about 2.5V for pot value from >> min to max (ignoring wire resistance etc.) >> >> It's a trivial exercise to solve for Rx as a function of ADC reading. >> >> Best regards, >> Spehro Pefhany >> -- >> "it's the network..." "The Journey is the reward" >> s...@interlog.com Info for manufacturers: >> http://www.trexon.com >> Embedded software/hardware/analog Info for designers: >> http://www.speff.com >> >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" s...@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist