R2 Project Log - Battery Monitor Circuit
After playing with R2’s circuit, I realized I had left no ADC ports for monitoring my battery! As it is a LiPo battery, it needs a low-voltage cutoff at 6v, or it will not be chargeable again. I built a simple circuit with an attiny13 and a potential divider, which will trigger an interrupt on my main processor when the battery voltage gets to 6.2v.
Circuit Diagram:
Code:
#define F_CPU 10000000UL #include <avr /io.h> #include <util /delay.h> // delay for up to 65k milliseconds void delayms(uint16_t millis) { // loop, delaying 1ms each iteration while ( millis ) { _delay_ms(1); millis--; } } // initialise the adc void init_adc ( void ) { //select external (VCC) voltage as the reference voltage (x0xx xxxx) ADMUX = 0x00; //enable ADC (1000 0000) ADCSRA |= 0x80; } // read the specified adc int adc_read ( uint8_t n ) { // set the adc to the chosen channel ADMUX = n; // start the ADC conversion, set the ADC clock to cpu clock / 16 (0100 0100) ADCSRA |= 0x44; // wait for the adc conversion to be completed while((ADCSRA & 0x40) !=0){}; // return the adc result return ADC; } int main(void) { // set PB0 to output DDRB |= 1< <PB3; // turn on the ADC init_adc(); // set up our variables int reading = 0, prev = 0, temp = 0; // loop for ever while(1) { // take a new adc reading reading = adc_read(2); // average it with the previous reading temp = (reading + prev) / 2; // if the voltage is less than 6 if ( temp > 185 ) { // turn the output pin on PORTB &= ~(1< <PB3); } else { // turn the output pin off PORTB |= 1<<PB3; /* LED off */ } // save the current reading prev = reading; // wait for 20ms delayms(20); } return 0; }
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