General Voltage Measurement
Once Vin is determined, the VCC can be calculated by the formula:
Vcc = Vin x (R1 + R2)/R2
Internal Analog Input Circuitry of the ADC
measure the VCC/Battery voltage without using any I/O pins or external components.
The core idea is to let the internal reference voltage Vbg act as ADC input,
and the target VCC act as ADC reference.
This solution helps the users setting up applications with low power consumption,
low MCU pin count, and/or few BOM parts.
For better resolution, this solution should be optimized due to its non-linearity.
In general voltage/battery monitoring, the solution is quite attractive.
Features
• VCC or battery voltage measurement
• No I/O pin occupying
• No external components
• Low power consumption
Example Code :
void setup() {
Serial.begin(9600);
}
void loop() {
ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
delay(2);
ADCSRA |= _BV(ADSC); // Start conversion
while (bit_is_set(ADCSRA,ADSC)); // measuring
uint8_t ADC_RES_L = ADCL;
uint8_t ADC_RES_H = ADCH;
float Vcc_value = ( 0x400 * 1.1 ) / (ADC_RES_L + ADC_RES_H * 0x100);
Serial.print(Vcc_value);
Serial.println("V");
delay(1000);
}
