root / toolbox / current.c @ e8960789
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1 | 10936c07 | Tom Mullins | #include "current.h" |
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2 | #include <avr/io.h> |
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3 | cbda92cc | Tom Mullins | #include <avr/interrupt.h> |
4 | #include <math.h> |
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5 | |||
6 | #define CYCLES_PER_SECOND 60 // wall power |
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7 | 975af07c | Tom Mullins | #define SAMPLES_PER_CYCLE 16 |
8 | #define N_SAMPLES 48 |
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9 | cbda92cc | Tom Mullins | |
10 | unsigned int samples[N_SAMPLES]; |
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11 | int sample_idx;
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12 | |||
13 | unsigned int sum; |
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14 | unsigned long sum_sq; |
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15 | 10936c07 | Tom Mullins | |
16 | void current_init() {
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17 | cbda92cc | Tom Mullins | |
18 | f4df665c | Tom Mullins | /* TODO reduce power consumption with DIDR* */
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19 | cbda92cc | Tom Mullins | |
20 | /*
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21 | f4df665c | Tom Mullins | * COM1A = COM1B = 0, disconnect pins
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22 | * WGM1 = 4, clear timer on compare A
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23 | db11713d | Tom Mullins | * CS1 = 1, no prescaler
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24 | cbda92cc | Tom Mullins | */
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25 | db11713d | Tom Mullins | TCCR1B = _BV(WGM12) | _BV(CS10); |
26 | cbda92cc | Tom Mullins | |
27 | f4df665c | Tom Mullins | /* Timer is cleared on A, ADC is triggered on B */
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28 | db11713d | Tom Mullins | OCR1A = F_CPU / SAMPLES_PER_CYCLE / CYCLES_PER_SECOND; |
29 | OCR1B = OCR1A; |
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30 | cbda92cc | Tom Mullins | |
31 | 10936c07 | Tom Mullins | /*
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32 | * REFS = 0, Vcc reference (set to 2 for internal 1.1V reference)
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33 | * MUX = 8, PB3(ADC8)
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34 | */
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35 | ADMUX = _BV(MUX3); |
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36 | cbda92cc | Tom Mullins | |
37 | 10936c07 | Tom Mullins | /*
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38 | * ADLAR = 0, right adjust result
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39 | f4df665c | Tom Mullins | * ADTS = 5, start on timer 1 compare match B
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40 | 10936c07 | Tom Mullins | */
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41 | f4df665c | Tom Mullins | ADCSRB = _BV(ADTS2) | _BV(ADTS0); |
42 | cbda92cc | Tom Mullins | |
43 | 10936c07 | Tom Mullins | /*
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44 | * ADEN = 1, enable
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45 | cbda92cc | Tom Mullins | * ADSC = 0, don't start yet
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46 | 10936c07 | Tom Mullins | * ADATE = 1, auto trigger
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47 | cbda92cc | Tom Mullins | * ADIE = 1, enable interrupt
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48 | db11713d | Tom Mullins | * ADPS = 6, prescale clock by 64
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49 | 10936c07 | Tom Mullins | */
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50 | db11713d | Tom Mullins | ADCSRA = _BV(ADEN) | _BV(ADATE) | _BV(ADIE) | _BV(ADPS2) | _BV(ADPS1); |
51 | 10936c07 | Tom Mullins | } |
52 | |||
53 | cbda92cc | Tom Mullins | ISR(ADC_vect) { |
54 | unsigned int old, new; |
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55 | |||
56 | db11713d | Tom Mullins | /* clear the timer interrupt flag so that the ADC will be triggered again
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57 | * next time the timer resets */
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58 | TIFR |= _BV(OCF1B); |
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59 | |||
60 | cbda92cc | Tom Mullins | new = ADC; |
61 | |||
62 | /* put sample into ring buffer */
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63 | old = samples[sample_idx]; |
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64 | samples[sample_idx++] = new; |
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65 | if (sample_idx == N_SAMPLES)
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66 | sample_idx = 0;
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67 | |||
68 | /* keep a running total of samples and samples squared */
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69 | sum += new; |
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70 | sum -= old; |
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71 | e8960789 | Tom Mullins | sum_sq += (unsigned long)new*new; |
72 | sum_sq -= (unsigned long)old*old; |
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73 | cbda92cc | Tom Mullins | } |
74 | |||
75 | unsigned int current_read() { |
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76 | unsigned int _sum; |
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77 | unsigned long _sum_sq; |
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78 | |||
79 | cli(); |
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80 | _sum = sum; |
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81 | _sum_sq = sum_sq; |
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82 | sei(); |
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83 | |||
84 | /* calculate the variance using sum and sum_sq */
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85 | 975af07c | Tom Mullins | return (N_SAMPLES*_sum_sq - (unsigned long)_sum*_sum) / |
86 | (N_SAMPLES*(N_SAMPLES-1));
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87 | 10936c07 | Tom Mullins | } |