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- /*
- * adc.cpp
- *
- * OpenChrono BB speed measurement device.
- *
- * https://provideyourown.com/2012/secret-arduino-voltmeter-measure-battery-voltage/
- */
-
- #include <Arduino.h>
-
- #include "adc.h"
-
- long readVcc(void) {
- // Read 1.1V reference against AVcc
- // set the reference to Vcc and the measurement to the internal 1.1V reference
- #if defined(__AVR_ATmega32U4__) || defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
- ADMUX = _BV(REFS0) | _BV(MUX4) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
- #elif defined (__AVR_ATtiny24__) || defined(__AVR_ATtiny44__) || defined(__AVR_ATtiny84__)
- ADMUX = _BV(MUX5) | _BV(MUX0);
- #elif defined (__AVR_ATtiny25__) || defined(__AVR_ATtiny45__) || defined(__AVR_ATtiny85__)
- ADMUX = _BV(MUX3) | _BV(MUX2);
- #else
- ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
- #endif
-
- delay(2); // Wait for Vref to settle
- ADCSRA |= _BV(ADSC); // Start conversion
- while (bit_is_set(ADCSRA,ADSC)); // measuring
-
- uint8_t low = ADCL; // must read ADCL first - it then locks ADCH
- uint8_t high = ADCH; // unlocks both
-
- long result = (high<<8) | low;
-
- result = 1125300L / result; // Calculate Vcc (in mV); 1125300 = 1.1*1023*1000
- return result; // Vcc in millivolts
- }
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