145 lines
3.1 KiB
C++
145 lines
3.1 KiB
C++
/***************************************************
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This is a library for the SHT31 Digital Humidity & Temp Sensor
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Designed specifically to work with the SHT31 Digital sensor from Adafruit
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----> https://www.adafruit.com/products/2857
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These sensors use I2C to communicate, 2 pins are required to interface
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Adafruit invests time and resources providing this open source code,
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please support Adafruit and open-source hardware by purchasing
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products from Adafruit!
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Written by Limor Fried/Ladyada for Adafruit Industries.
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BSD license, all text above must be included in any redistribution
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****************************************************/
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#include "Adafruit_SHT31.h"
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Adafruit_SHT31::Adafruit_SHT31() {
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_i2caddr = NULL;
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humidity = 0.0f;
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temp = 0.0f;
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}
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boolean Adafruit_SHT31::begin(uint8_t i2caddr) {
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Wire.begin();
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_i2caddr = i2caddr;
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reset();
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// return (readStatus() == 0x40);
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return true;
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}
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uint16_t Adafruit_SHT31::readStatus(void) {
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writeCommand(SHT31_READSTATUS);
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Wire.requestFrom(_i2caddr, (uint8_t)3);
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uint16_t stat = Wire.read();
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stat <<= 8;
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stat |= Wire.read();
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// Serial.println(stat, HEX);
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return stat;
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}
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void Adafruit_SHT31::reset(void) {
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writeCommand(SHT31_SOFTRESET);
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delay(10);
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}
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void Adafruit_SHT31::heater(boolean h) {
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if (h)
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writeCommand(SHT31_HEATEREN);
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else
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writeCommand(SHT31_HEATERDIS);
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}
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float Adafruit_SHT31::readTemperature(void) {
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if (!readTempHum())
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return NAN;
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return temp;
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}
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float Adafruit_SHT31::readHumidity(void) {
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if (!readTempHum())
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return NAN;
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return humidity;
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}
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boolean Adafruit_SHT31::readTempHum(void) {
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uint8_t readbuffer[6];
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writeCommand(SHT31_MEAS_HIGHREP);
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delay(20);
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Wire.requestFrom(_i2caddr, (uint8_t)6);
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if (Wire.available() != 6)
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return false;
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for (uint8_t i = 0; i < 6; i++) {
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readbuffer[i] = Wire.read();
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// Serial.print("0x"); Serial.println(readbuffer[i], HEX);
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}
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uint16_t ST, SRH;
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ST = readbuffer[0];
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ST <<= 8;
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ST |= readbuffer[1];
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if (readbuffer[2] != crc8(readbuffer, 2))
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return false;
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SRH = readbuffer[3];
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SRH <<= 8;
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SRH |= readbuffer[4];
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if (readbuffer[5] != crc8(readbuffer + 3, 2))
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return false;
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// Serial.print("ST = "); Serial.println(ST);
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double stemp = ST;
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stemp *= 175;
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stemp /= 0xffff;
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stemp = -45 + stemp;
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temp = stemp;
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// Serial.print("SRH = "); Serial.println(SRH);
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double shum = SRH;
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shum *= 100;
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shum /= 0xFFFF;
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humidity = shum;
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return true;
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}
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void Adafruit_SHT31::writeCommand(uint16_t cmd) {
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Wire.beginTransmission(_i2caddr);
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Wire.write(cmd >> 8);
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Wire.write(cmd & 0xFF);
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Wire.endTransmission();
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}
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uint8_t Adafruit_SHT31::crc8(const uint8_t *data, int len) {
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/*
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*
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* CRC-8 formula from page 14 of SHT spec pdf
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*
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* Test data 0xBE, 0xEF should yield 0x92
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*
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* Initialization data 0xFF
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* Polynomial 0x31 (x8 + x5 +x4 +1)
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* Final XOR 0x00
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*/
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const uint8_t POLYNOMIAL(0x31);
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uint8_t crc(0xFF);
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for (int j = len; j; --j) {
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crc ^= *data++;
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for (int i = 8; i; --i) {
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crc = (crc & 0x80) ? (crc << 1) ^ POLYNOMIAL : (crc << 1);
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}
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}
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return crc;
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}
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