I am using the ATmega644 as a low quality voltmeter to test out both ADC and my LCD display. Everything works great when using an external 5V reference, but as soon as I switch ADMUX from 0b00100000 to 0b11100000 (enabling the 2.56V reference) the ADC starts to read maximum voltage even at 0V at my input. I did disconnected the reference pin from 5V and did put a capacitor from ground to it, but it stays at the maximum 256. Any ideas why it will work for an external voltage but not an internal reference voltage?
Joined: Sun. Oct 28, 2007
Posts: 201 View posts
Location: Southeastern Michigan, USA