NEX ROBOTICS FIREBIRD V ATMEGA 2560 Hardware Manual page 67

3.19.2 Battery voltage sensing
Filtered battery voltage is used for battery voltage sensing. Analog to Digital Converter (ADC)
can measure maximum voltage of 5V. Hence battery voltage is scaled down from 8-15V to less
than 5V using resistor divider network formed by R12 and R13. It scales down the voltage by
approximately 1/3 of the actual value.
ATMEGA2560 ADC can be used in 8 bit or 10 bit resolution. To calculate voltage from the
ADC's acquired digital value in 8 bit resolution we use following formula:
V Battery = 0.7V + (ADC value * (5V/255) * ((10K + 3.3K) / 3.3K))
V Battery = 0.7V + (ADC value * 0.0790)
In the above formula:
0.7V represents voltage drop across the diodes D7 and D9. for more details refer to figure
•
3.11.
5V/255 represents the ADC step resolution
•
(10K + 3.3K) / 3.3K is a voltage divider formula
•
Note: For 10 bit resolution replace 255 by 1024.
© NEX Robotics Pvt. Ltd. and ERTS Lab, CSE, IIT Bombay, INDIA
Figure 3.60: Battery Voltage Divider Bias Circuit
Fire Bird V ATMEGA2560 Hardware Manual
67