root / toolbox / current.c @ cbda92cc
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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 | #define SAMPLES_PER_CYCLE 10 |
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8 | #define N_SAMPLES 20 |
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9 | |||
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 | /*
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19 | * COM0A = 0, disconnect pin
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20 | * WGM0 = 2, clear timer on compare
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21 | */
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22 | TCCR0A |= _BV(WGM01); |
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23 | |||
24 | /*
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25 | * CS0 = 5, 1024 prescaler
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26 | */
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27 | TCCR0B |= _BV(CS02) | _BV(CS00); |
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28 | |||
29 | OCR0A = F_CPU / 1024 / SAMPLES_PER_CYCLE / CYCLES_PER_SECOND;
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30 | |||
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 | /* TODO reduce power consumption with DIDR* */
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38 | cbda92cc | Tom Mullins | |
39 | 10936c07 | Tom Mullins | /*
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40 | * ADLAR = 0, right adjust result
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41 | cbda92cc | Tom Mullins | * ADTS = 3, start on timer 0 compare match A
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42 | 10936c07 | Tom Mullins | */
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43 | cbda92cc | Tom Mullins | ADCSRB = _BV(ADTS1) | _BV(ADTS0); |
44 | |||
45 | 10936c07 | Tom Mullins | /*
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46 | * ADEN = 1, enable
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47 | cbda92cc | Tom Mullins | * ADSC = 0, don't start yet
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48 | 10936c07 | Tom Mullins | * ADATE = 1, auto trigger
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49 | cbda92cc | Tom Mullins | * ADIE = 1, enable interrupt
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50 | * ADPS = 4, prescale clock by 16
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51 | 10936c07 | Tom Mullins | */
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52 | cbda92cc | Tom Mullins | ADCSRA |= _BV(ADEN) | _BV(ADATE) | _BV(ADIE) | _BV(ADPS2); |
53 | 10936c07 | Tom Mullins | } |
54 | |||
55 | cbda92cc | Tom Mullins | ISR(ADC_vect) { |
56 | unsigned int old, new; |
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57 | |||
58 | new = ADC; |
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59 | |||
60 | /* put sample into ring buffer */
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61 | old = samples[sample_idx]; |
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62 | samples[sample_idx++] = new; |
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63 | if (sample_idx == N_SAMPLES)
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64 | sample_idx = 0;
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65 | |||
66 | /* keep a running total of samples and samples squared */
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67 | sum += new; |
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68 | sum -= old; |
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69 | sum_sq += new*new; |
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70 | sum_sq -= old*old; |
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71 | } |
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72 | |||
73 | /*unsigned char isqrt(unsigned int x) {
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74 | unsigned int sqrt, mulmask;
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75 | sqrt = 0;
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76 | mulmask = 0x80;
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77 | if (x > 0) {
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78 | while (mulmask) {
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79 | sqrt |= mulmask;
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80 | if (sqrt * sqrt > x)
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81 | sqrt &= ~mulmask;
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82 | mulmask >>= 1;
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83 | }
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84 | }
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85 | return sqrt;
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86 | }*/
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87 | |||
88 | unsigned int current_read() { |
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89 | unsigned int _sum; |
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90 | unsigned long _sum_sq; |
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91 | |||
92 | cli(); |
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93 | _sum = sum; |
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94 | _sum_sq = sum_sq; |
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95 | sei(); |
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96 | |||
97 | /* calculate the variance using sum and sum_sq */
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98 | return (N_SAMPLES*_sum_sq - _sum*_sum) / (N_SAMPLES*(N_SAMPLES-1)); |
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99 | 10936c07 | Tom Mullins | } |