Revision cbda92cc
Untested current RMS calculation
It's not actually RMS, it's variance. Same general idea.
toolbox/current.c | ||
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#include "current.h" |
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#include <avr/io.h> |
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#include <avr/interrupt.h> |
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#include <math.h> |
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#define CYCLES_PER_SECOND 60 // wall power |
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#define SAMPLES_PER_CYCLE 10 |
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#define N_SAMPLES 20 |
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unsigned int samples[N_SAMPLES]; |
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int sample_idx; |
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unsigned int sum; |
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unsigned long sum_sq; |
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void current_init() { |
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/* |
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* COM0A = 0, disconnect pin |
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* WGM0 = 2, clear timer on compare |
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*/ |
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TCCR0A |= _BV(WGM01); |
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/* |
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* CS0 = 5, 1024 prescaler |
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*/ |
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TCCR0B |= _BV(CS02) | _BV(CS00); |
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OCR0A = F_CPU / 1024 / SAMPLES_PER_CYCLE / CYCLES_PER_SECOND; |
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/* |
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* REFS = 0, Vcc reference (set to 2 for internal 1.1V reference) |
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* MUX = 8, PB3(ADC8) |
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*/ |
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ADMUX = _BV(MUX3); |
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/* TODO reduce power consumption with DIDR* */ |
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/* |
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* ADLAR = 0, right adjust result |
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* ADTS = 0, free running mode
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* ADTS = 3, start on timer 0 compare match A
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*/ |
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ADCSRB = 0; |
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ADCSRB = _BV(ADTS1) | _BV(ADTS0); |
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/* |
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* ADEN = 1, enable |
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* ADSC = 1, start now
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* ADSC = 0, don't start yet
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* ADATE = 1, auto trigger |
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* ADIE = 0, disable interrupt
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* ADPS = 3, prescale clock by 8
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* ADIE = 1, enable interrupt
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* ADPS = 4, prescale clock by 16
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*/ |
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ADCSRA |= _BV(ADEN) | _BV(ADSC) | _BV(ADATE) | _BV(ADPS1) | _BV(ADPS0);
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ADCSRA |= _BV(ADEN) | _BV(ADATE) | _BV(ADIE) | _BV(ADPS2);
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} |
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int current_read() { |
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return ADC; |
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ISR(ADC_vect) { |
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unsigned int old, new; |
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new = ADC; |
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/* put sample into ring buffer */ |
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old = samples[sample_idx]; |
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samples[sample_idx++] = new; |
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if (sample_idx == N_SAMPLES) |
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sample_idx = 0; |
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/* keep a running total of samples and samples squared */ |
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sum += new; |
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sum -= old; |
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sum_sq += new*new; |
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sum_sq -= old*old; |
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} |
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/*unsigned char isqrt(unsigned int x) { |
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unsigned int sqrt, mulmask; |
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sqrt = 0; |
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mulmask = 0x80; |
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if (x > 0) { |
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while (mulmask) { |
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sqrt |= mulmask; |
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if (sqrt * sqrt > x) |
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sqrt &= ~mulmask; |
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mulmask >>= 1; |
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} |
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} |
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return sqrt; |
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}*/ |
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unsigned int current_read() { |
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unsigned int _sum; |
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unsigned long _sum_sq; |
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cli(); |
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_sum = sum; |
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_sum_sq = sum_sq; |
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sei(); |
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/* calculate the variance using sum and sum_sq */ |
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return (N_SAMPLES*_sum_sq - _sum*_sum) / (N_SAMPLES*(N_SAMPLES-1)); |
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} |
toolbox/current.h | ||
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#define CURRENT_H |
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void current_init(); |
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int current_read(); |
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unsigned int current_read();
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#endif |
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