I will put this on my list of things to try. 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: "M. Adam Davis" To: "Microcontroller discussion list - Public." Sent: Wednesday, May 07, 2008 10:54 AM Subject: Re: [PIC]Analog signal conditioning > 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 > > On 5/7/08, John Ferrell wrote: >> Yes but that requires access at the tower top. >> Also, I don't think the pot is a significant factor in the problem. >> >> Essentially I am trying to duplicate an ohm meter. It is interesting that >> MicroChip offers special purpose chips for Ohm meters. >> >> 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: "Michael Rigby-Jones" >> To: "Microcontroller discussion list - Public." >> Sent: Wednesday, May 07, 2008 5:11 AM >> Subject: RE: [PIC]Analog signal conditioning >> >> >> > >> > >> >> -----Original Message----- >> >> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On >> > Behalf >> >> Of John Ferrell >> >> Sent: 06 May 2008 20:31 >> >> To: Microcontroller discussion list - Public. >> >> Subject: Re: [PIC]Analog signal conditioning >> >> >> >> Until I fell into the trap I would have agreed with you. The AP Notes >> >> regarding ADC are serious reading. >> >> If you keep the pot onboard with the PIC you can get away with a lot. >> >> Reading the wiper of a 5K pot across Vcc and ground is not a problem. >> >> >> >> My Pot is at the end of about 75 feet of cable. The cable contributes >> > some >> >> unknown reactance in the configuration. The troublesome noise is a >> >> byproduct >> >> of the conversion within the PIC. The current requirements are likely >> > to >> >> be >> >> damaging to the Pot (500 ohms) if I simply put Vcc across it... I have >> > a >> >> 4.3K resistor in series with it. >> >> >> >> The conclusion that I draw at this time is that remote sensing is not >> > a >> >> simple matter even if it is just a resistor. >> >> >> > >> > Did you see my original post on differential measurement? >> > >> > Mike >> > >> > ======================================================================= >> > This e-mail is intended for the person it is addressed to only. The >> > information contained in it may be confidential and/or protected by >> > law. If you are not the intended recipient of this message, you must >> > not make any use of this information, or copy or show it to any >> > person. Please contact us immediately to tell us that you have >> > received this e-mail, and return the original to us. Any use, >> > forwarding, printing or copying of this message is strictly prohibited. >> > No part of this message can be considered a request for goods or >> > services. >> > ======================================================================= >> > >> > -- >> > 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 >> > > > -- > EARTH DAY 2008 > Tuesday April 22 > Save Money * Save Oil * Save Lives * Save the Planet > http://www.driveslowly.org > -- > 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