Sounds like your voltage follower doesn’t have enough grunt to drive the ADC.  Where are you measuring the 0.8 volts?  At the input to the buffer or at its output?



From: Keane, Ben (STRX) []
Sent: Tuesday, May 22, 2012 2:31 PM
To: General mailing list for gumstix users.
Subject: [Gumstix-users] ADC characteristics


Hello Mailing List,


I am wondering if anyone has characterized the ADC's on the gumstix?  I am experiencing a non-linear response... depending on the buffers (on a custom board) output resistance, the characteristic changes. It seems that until the ADC value reaches 0.8V with a measured current draw of 0.24mA the ADC will just measure 0... After that point, it will start to measure linearly.  When driven directly from the power supply the voltage response is linear, but when diven from an voltage follower, it is not.


Any help would be much appreciated.


Many Thanks,













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