but, but...your A2D converter on the PIC is isolated from the divider. You have a unity gain follower after the divider and then a difference amp which has a very low output impedance. So why should the divider have any affect on the A2D..as far as the PIC RA1 input is concerned there is a voltage source with a very low impedance it is looking at. Am I missing something obvious here? Madhu >-----Original Message----- >From: pic microcontroller discussion list >[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Alexander Rice >Sent: Saturday, March 13, 2004 3:51 AM >To: PICLIST@MITVMA.MIT.EDU >Subject: Re: [EE:] Measuring Current in a High Voltage Circuit > > >On Fri, 12 Mar 2004 15:29:05 -0500, Roberts II, Charles K. > wrote: > >> Hello All >> >> I am working on a PIC based High Voltage module. The schematic of the >> current meter portion of the module is attached. I am measuring the >> voltage drop across a knowm resistor, but to do it I had to use two >> voltage dividers to bring the levels to something I can read. I measure >> about the same current with or without a load. What could be going on? >> Loooking into the devider there are 50Meg Ohms to Ground, Is this what >> is messing up my reading? > >Quite possibly, i don't think that the source impedence for the A2D >modules is reccomended to be greater then 10K Ohms, try putting a 0.1uF >capacitor across it to lower the impedence during A2D. > >Regards > >Alex Rice -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads