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95 lines
2.6 KiB
C++
95 lines
2.6 KiB
C++
//
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// FILE: ACS712.cpp
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// AUTHOR: Rob Tillaart, Pete Thompson
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// VERSION: 0.2.1
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// DATE: 2020-08-02
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// PURPOSE: ACS712 library - current measurement
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//
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// HISTORY:
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// 0.1.0 2020-03-17 initial version
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// 0.1.1 2020-03-18 first release version
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// 0.1.2 2020-03-21 automatic formfactor test
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// 0.1.3 2020-05-27 fix library.json
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// 0.1.4 2020-08-02 Allow for faster processors
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// 0.2.0 2020-08-02 Add autoMidPoint
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// 0.2.1 2020-12-06 Add arduino-CI + readme + unittest + refactor
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#include "ACS712.h"
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ACS712::ACS712(uint8_t analogPin, float volts, uint16_t maxADC, uint8_t mVperA)
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{
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_pin = analogPin;
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_mVpstep = 1000.0 * volts / maxADC; // 1x 1000 for V -> mV
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_mVperAmpere = mVperA;
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_formFactor = 0.70710678119; // 0.5 * sqrt(2); TODO: should be smaller in practice 0.5 ?
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_midPoint = maxADC / 2;
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_noisemV = 21; // Noise is 21mV according to datasheet
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}
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int ACS712::mA_AC(uint8_t freq)
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{
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uint32_t start = micros();
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uint16_t period = ((freq == 60) ? 16670 : 20000);
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uint16_t samples = 0;
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uint16_t zeros = 0;
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int _min, _max;
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_min = _max = analogRead(_pin);
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while (micros() - start < period) // UNO ~180 samples...
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{
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samples++;
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int val = analogRead(_pin);
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if (val < _min) _min = val;
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if (val > _max) _max = val;
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if (abs(val - _midPoint) <= (_noisemV/_mVpstep)) zeros++;
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}
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int point2point = (_max - _min);
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// automatic determine _formFactor / crest factor
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float D = 0;
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float FF = 0;
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if (zeros > samples * 0.025)
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{
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D = 1.0 - (1.0 * zeros) / samples; // % SAMPLES NONE ZERO
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FF = sqrt(D) * 0.5 * sqrt(2); // ASSUME NON ZERO PART ~ SINUS
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}
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else // # zeros is small => D --> 1 --> sqrt(D) --> 1
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{
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FF = 0.5 * sqrt(2);
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}
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_formFactor = FF;
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// math could be partially precalculated: C = 1000.0 * 0.5 * _mVpstep / _mVperAmpere;
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// rounding?
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return 1000.0 * 0.5 * point2point * _mVpstep * _formFactor / _mVperAmpere;
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}
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int ACS712::mA_DC()
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{
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// read twice to stabilize...
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analogRead(_pin);
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int steps = analogRead(_pin) - _midPoint;
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return 1000.0 * steps * _mVpstep / _mVperAmpere;
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}
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// configure by sampling for 2 cycles of AC
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// Also works for DC as long as no current flowing
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void ACS712::autoMidPoint(uint8_t freq)
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{
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uint32_t start = micros();
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uint16_t twoPeriods = ((freq == 60) ? 16670 : 20000) * 2;
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uint32_t total = 0;
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uint32_t samples = 0;
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while (micros() - start < twoPeriods) {
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uint16_t reading = analogRead(_pin);
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total += reading;
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samples ++;
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// Delaying ensures we won't overflow since we'll perform a maximum of 40,000 reads
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delayMicroseconds(1);
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}
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_midPoint = total / samples;
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}
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// END OF FILE
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