What I meant was to put the divider on the output side of the voltage follo= wer, thats lower impedance. ----- Original Message ----- From: Bob Ammerman To: Microcontroller discussion list - Public. Cc:=20 Sent: Friday, April 27, 2012 11:51 AM Subject: Re: [PIC] ADC interface to hiZ source If the source impedance is really 20Mohm, a 100K/100K divider isn't going t= o=20 work. It will load the source extremely. I am guessing the source impedance is really much, much less than 20Mohm. I= =20 would verify this with your customer before proceeding. -- Bob Ammerman RAm Systems ----- Original Message -----=20 From: "alan smith" To: "Microcontroller discussion list - Public." Sent: Friday, April 27, 2012 1:32 PM Subject: [PIC] ADC interface to hiZ source I've done some searching around, with some mixed results on the proper=20 interface. Since the source is 0-10V but 20Mohms (according to the customer), at=20 minimum I plan on a 100K/100K divider to range it to 0-5V, and a zener clam= p=20 for the ...just in case...since this is an industrial application. Now, I was thinking...and this is where I've seen it both ways....that I=20 really want to use a voltage follower on the input, that feeds the divider?= =20 This gives a lower impedance input to the PIC's ADC input. But I've seen it= =20 where some have said...not necessary... So? what are the reasons for the opamp (other than stated for impedance=20 interfacing) or just the divider network? --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist=20 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .