Re: [AVR-Chat] adc wont read below 0.8v?
2007-06-07 by A F
Whoever said ground issue, you win the secret prize. Im using an stk500 which has a diode on ground for reverse polarity protection. Sure would be nice if the users guide mentioned something about that. So I moved the breadboard ground from the bench supply to the stk board and all is well. Thanks for the help. --Aaron
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----- Original Message ---- From: A F <afaupell@yahoo.com> To: AVR-Chat@yahoogroups.com Sent: Monday, June 4, 2007 8:01:59 PM Subject: Re: [AVR-Chat] adc wont read below 0.8v? The stk500 and my breadboard are both driven from my bench supply so the ground should be good. I am using the adc on port c pin 4. It is being driven directly by an LM34 temp sensor or a pot for testing so I think the impedence is low. the alternate function for this pin is sda but TWEN is set to 0. I have set PUD to 1 in testing just to make sure all the pullups are off. I do see some ringing on the input but its only 120mv peak. could letting the adc input exceed aref cause damage that would manifest in this manner? any other ideas? thanks for all the suggestions. --Aaron ----- Original Message ---- From: David VanHorn <microbrix@gmail. com> To: AVR-Chat@yahoogroup s.com Sent: Monday, June 4, 2007 6:28:23 PM Subject: Re: [AVR-Chat] adc wont read below 0.8v? On 6/4/07, Jim Wagner <jim_d_wagner@ applelinks. net> wrote: > Some devices allow interrnal pullup to remain on in ADC > mode. Check that pullups, etc, are off on those pins. That could well be it, or the sourcing impedance is too high on whatever is driving the pins. There is a certain amount of leakage current possible, that might be giving you anomalously high voltages. IIRC they want the source impedance below 10k. ____________ _________ _________ _________ _________ _________ _ Moody friends. Drama queens. Your life? Nope! - their life, your story. Play Sims Stories at Yahoo! Games. http://sims. yahoo.com/ [Non-text portions of this message have been removed] ____________________________________________________________________________________ Finding fabulous fares is fun. Let Yahoo! FareChase search your favorite travel sites to find flight and hotel bargains. http://farechase.yahoo.com/promo-generic-14795097 [Non-text portions of this message have been removed]