Canberk Sönmez
/
SHT21
A simple example adopting SHT21 Arduino library to mbed.
SHT21.cpp
- Committer:
- odtulumbedder
- Date:
- 2017-09-13
- Revision:
- 1:f4a1942b4486
File content as of revision 1:f4a1942b4486:
#include "SHT21.hpp" const uint16_t SHT21::POLYNOMIAL = 0x131; SHT21::SHT21(PinName sda, PinName scl, char addr) : addr_(addr), pi2c_(new I2C(sda, scl)), i2c_(*pi2c_) { } SHT21::SHT21(I2C &i2c, char addr) : addr_(addr), pi2c_(NULL), i2c_(i2c) { } float SHT21::temperature() { uint16_t r = readRaw(TRIGGER_T_MEASUREMENT_HM); r &= ~0x0003; return (-46.85 + 175.72/65536 * (float) r); } float SHT21::humidity() { uint16_t r = readRaw(TRIGGER_RH_MEASUREMENT_HM); r &= ~0x0003; return (-6.0 + 125.0/65536 * (float) r); } void SHT21::reset() { uint8_t pcmd [] = { SOFT_RESET }; i2c_.write(addr_, (const char *) pcmd, 1); wait_ms(15); } void SHT21::serialNumber(uint8_t *serialNumber) { uint8_t data[8]; uint8_t pcmd0[2] = { 0xFA, 0x0F }; uint8_t pcmd1[2] = { 0xFC, 0xC9 }; uint8_t i = 0; i2c_.write(addr_, (const char *) pcmd0, 2); i2c_.read(addr_, (char *) data, 8); serialNumber[5] = data[i++]; i++; serialNumber[4] = data[i++]; i++; serialNumber[3] = data[i++]; i++; serialNumber[2] = data[i++]; i = 0; i2c_.write(addr_, (const char *) pcmd1, 2); i2c_.read(addr_, (char *) data, 6); serialNumber[1] = data[i++]; serialNumber[0] = data[i++]; i++; serialNumber[7] = data[i++]; serialNumber[8] = data[i++]; i = 0; } SHT21::~SHT21() { if (pi2c_) delete pi2c_; } uint16_t SHT21::readRaw(uint8_t cmd) { uint8_t checksum; uint8_t data[2]; uint16_t result; uint8_t pcmd [] = { cmd }; i2c_.write(addr_, (const char *) pcmd, 1); i2c_.read(addr_, (char *) data, 2); i2c_.read(addr_, (char *) &checksum, 1); result = data[0] << 8; result += data[1]; if (crcChecksum(data, 2, checksum)) { reset(); return 1; } return result; } bool SHT21::crcChecksum(const uint8_t *data, uint8_t sz, uint8_t checksum) { uint8_t crc = 0; for (uint8_t i = 0; i < sz; ++i) { crc ^= data[i]; for (uint8_t j /* bit index */ = 8; j > 0; --j) { if (crc & 0x80) crc = (crc << 1) ^ POLYNOMIAL; else crc = (crc << 1); } } return crc == checksum; }