I am trying to measure a battery voltage ( 2 * AAA Batteries ) via a voltage divider connected with an ADC pin of ATmega169PA. The voltage divider is of 43k ( top - battery ) and 20k ( bottom - gnd ) and a 100nf capacitor connected in parallel with 20k resistor. Without connecting a voltage divider to ADC pin and when I measure the voltage using DMM , I get a voltage reading of .984V which is almost correct.
But the moment I connect the voltage divider to the ADC pin the voltage changes to 1.413V ( read by same DMM ). Any idea of what is happening ? Is it because of 10K of ADC impedance boundary ?
I measure the samples once in every 500ms . I am using Internal 1.1V Voltage Reference with external capacitor at AREF pin. ADC input pin is configured correctly and also the DIDR0 for the respective ADC pin.