Canberk Sönmez / Mbed 2 deprecated SHT21

A simple example adopting SHT21 Arduino library to mbed.

Dependencies:   mbed

main.cpp@0:062188c0bb61, 2017-08-10 (annotated)

Committer:
odtulumbedder
Date:
Thu Aug 10 13:25:37 2017 +0000
Revision:
0:062188c0bb61
Child:
1:f4a1942b4486
Initial Commit

Who changed what in which revision?

UserRevisionLine numberNew contents of line
odtulumbedder 0:062188c0bb61 1 #include "mbed.h"
odtulumbedder 0:062188c0bb61 2
odtulumbedder 0:062188c0bb61 3 /**
odtulumbedder 0:062188c0bb61 4 * A simple library for SHT21 humidity and temperature sensor.
odtulumbedder 0:062188c0bb61 5 * Based on the Arduino library.
odtulumbedder 0:062188c0bb61 6 */
odtulumbedder 0:062188c0bb61 7
odtulumbedder 0:062188c0bb61 8 class SHT21 {
odtulumbedder 0:062188c0bb61 9 public:
odtulumbedder 0:062188c0bb61 10 SHT21(PinName sda, PinName scl, char addr = (0x40 << 1));
odtulumbedder 0:062188c0bb61 11 SHT21(I2C &i2c, char addr = (0x40 << 1));
odtulumbedder 0:062188c0bb61 12
odtulumbedder 0:062188c0bb61 13 float temperature();
odtulumbedder 0:062188c0bb61 14 float humidity();
odtulumbedder 0:062188c0bb61 15
odtulumbedder 0:062188c0bb61 16 void reset();
odtulumbedder 0:062188c0bb61 17 void serialNumber(uint8_t *serialNumber);
odtulumbedder 0:062188c0bb61 18
odtulumbedder 0:062188c0bb61 19 ~SHT21();
odtulumbedder 0:062188c0bb61 20 private:
odtulumbedder 0:062188c0bb61 21 enum commands {
odtulumbedder 0:062188c0bb61 22 TRIGGER_T_MEASUREMENT_HM = 0xE3,
odtulumbedder 0:062188c0bb61 23 TRIGGER_RH_MEASUREMENT_HM = 0xE5,
odtulumbedder 0:062188c0bb61 24 TRIGGER_T_MEASUREMENT_NHM = 0xF3,
odtulumbedder 0:062188c0bb61 25 TRIGGER_RH_MEASUREMENT_NHM = 0xF5,
odtulumbedder 0:062188c0bb61 26 USER_REGISTER_W = 0xE6,
odtulumbedder 0:062188c0bb61 27 USER_REGISTER_R = 0xE7,
odtulumbedder 0:062188c0bb61 28 SOFT_RESET = 0xFE
odtulumbedder 0:062188c0bb61 29 };
odtulumbedder 0:062188c0bb61 30
odtulumbedder 0:062188c0bb61 31 static const uint16_t POLYNOMIAL;
odtulumbedder 0:062188c0bb61 32
odtulumbedder 0:062188c0bb61 33 char addr_;
odtulumbedder 0:062188c0bb61 34 I2C *pi2c_;
odtulumbedder 0:062188c0bb61 35 I2C &i2c_;
odtulumbedder 0:062188c0bb61 36
odtulumbedder 0:062188c0bb61 37 uint16_t readRaw(uint8_t cmd);
odtulumbedder 0:062188c0bb61 38 static bool crcChecksum(const uint8_t *data, uint8_t sz, uint8_t checksum);
odtulumbedder 0:062188c0bb61 39 };
odtulumbedder 0:062188c0bb61 40
odtulumbedder 0:062188c0bb61 41 const uint16_t SHT21::POLYNOMIAL = 0x131;
odtulumbedder 0:062188c0bb61 42
odtulumbedder 0:062188c0bb61 43 SHT21::SHT21(PinName sda, PinName scl, char addr) :
odtulumbedder 0:062188c0bb61 44 addr_(addr),
odtulumbedder 0:062188c0bb61 45 pi2c_(new I2C(sda, scl)),
odtulumbedder 0:062188c0bb61 46 i2c_(*pi2c_) {
odtulumbedder 0:062188c0bb61 47 }
odtulumbedder 0:062188c0bb61 48
odtulumbedder 0:062188c0bb61 49 SHT21::SHT21(I2C &i2c, char addr) :
odtulumbedder 0:062188c0bb61 50 addr_(addr),
odtulumbedder 0:062188c0bb61 51 pi2c_(NULL),
odtulumbedder 0:062188c0bb61 52 i2c_(i2c) {
odtulumbedder 0:062188c0bb61 53 }
odtulumbedder 0:062188c0bb61 54
odtulumbedder 0:062188c0bb61 55 float SHT21::temperature() {
odtulumbedder 0:062188c0bb61 56 uint16_t r = readRaw(TRIGGER_T_MEASUREMENT_HM);
odtulumbedder 0:062188c0bb61 57 r &= ~0x0003;
odtulumbedder 0:062188c0bb61 58 return (-46.85 + 175.72/65536 * (float) r);
odtulumbedder 0:062188c0bb61 59 }
odtulumbedder 0:062188c0bb61 60
odtulumbedder 0:062188c0bb61 61 float SHT21::humidity() {
odtulumbedder 0:062188c0bb61 62 uint16_t r = readRaw(TRIGGER_RH_MEASUREMENT_HM);
odtulumbedder 0:062188c0bb61 63 r &= ~0x0003;
odtulumbedder 0:062188c0bb61 64 return (-6.0 + 125.0/65536 * (float) r);
odtulumbedder 0:062188c0bb61 65 }
odtulumbedder 0:062188c0bb61 66
odtulumbedder 0:062188c0bb61 67 void SHT21::reset() {
odtulumbedder 0:062188c0bb61 68 uint8_t pcmd [] = { SOFT_RESET };
odtulumbedder 0:062188c0bb61 69 i2c_.write(addr_, (const char *) pcmd, 1);
odtulumbedder 0:062188c0bb61 70 wait_ms(15);
odtulumbedder 0:062188c0bb61 71 }
odtulumbedder 0:062188c0bb61 72
odtulumbedder 0:062188c0bb61 73 void SHT21::serialNumber(uint8_t *serialNumber) {
odtulumbedder 0:062188c0bb61 74 uint8_t data[8];
odtulumbedder 0:062188c0bb61 75 uint8_t pcmd0[2] = { 0xFA, 0x0F };
odtulumbedder 0:062188c0bb61 76 uint8_t pcmd1[2] = { 0xFC, 0xC9 };
odtulumbedder 0:062188c0bb61 77 uint8_t i = 0;
odtulumbedder 0:062188c0bb61 78 i2c_.write(addr_, (const char *) pcmd0, 2);
odtulumbedder 0:062188c0bb61 79 i2c_.read(addr_, (char *) data, 8);
odtulumbedder 0:062188c0bb61 80
odtulumbedder 0:062188c0bb61 81 serialNumber[5] = data[i++];
odtulumbedder 0:062188c0bb61 82 i++;
odtulumbedder 0:062188c0bb61 83 serialNumber[4] = data[i++];
odtulumbedder 0:062188c0bb61 84 i++;
odtulumbedder 0:062188c0bb61 85 serialNumber[3] = data[i++];
odtulumbedder 0:062188c0bb61 86 i++;
odtulumbedder 0:062188c0bb61 87 serialNumber[2] = data[i++];
odtulumbedder 0:062188c0bb61 88 i = 0;
odtulumbedder 0:062188c0bb61 89
odtulumbedder 0:062188c0bb61 90 i2c_.write(addr_, (const char *) pcmd1, 2);
odtulumbedder 0:062188c0bb61 91 i2c_.read(addr_, (char *) data, 6);
odtulumbedder 0:062188c0bb61 92
odtulumbedder 0:062188c0bb61 93 serialNumber[1] = data[i++];
odtulumbedder 0:062188c0bb61 94 serialNumber[0] = data[i++];
odtulumbedder 0:062188c0bb61 95 i++;
odtulumbedder 0:062188c0bb61 96 serialNumber[7] = data[i++];
odtulumbedder 0:062188c0bb61 97 serialNumber[8] = data[i++];
odtulumbedder 0:062188c0bb61 98 i = 0;
odtulumbedder 0:062188c0bb61 99 }
odtulumbedder 0:062188c0bb61 100
odtulumbedder 0:062188c0bb61 101 SHT21::~SHT21() {
odtulumbedder 0:062188c0bb61 102 if (pi2c_) delete pi2c_;
odtulumbedder 0:062188c0bb61 103 }
odtulumbedder 0:062188c0bb61 104
odtulumbedder 0:062188c0bb61 105 uint16_t SHT21::readRaw(uint8_t cmd) {
odtulumbedder 0:062188c0bb61 106 uint8_t checksum;
odtulumbedder 0:062188c0bb61 107 uint8_t data[2];
odtulumbedder 0:062188c0bb61 108 uint16_t result;
odtulumbedder 0:062188c0bb61 109
odtulumbedder 0:062188c0bb61 110 uint8_t pcmd [] = { cmd };
odtulumbedder 0:062188c0bb61 111
odtulumbedder 0:062188c0bb61 112 i2c_.write(addr_, (const char *) pcmd, 1);
odtulumbedder 0:062188c0bb61 113 i2c_.read(addr_, (char *) data, 2);
odtulumbedder 0:062188c0bb61 114 i2c_.read(addr_, (char *) &checksum, 1);
odtulumbedder 0:062188c0bb61 115
odtulumbedder 0:062188c0bb61 116 result = data[0] << 8;
odtulumbedder 0:062188c0bb61 117 result += data[1];
odtulumbedder 0:062188c0bb61 118
odtulumbedder 0:062188c0bb61 119 if (crcChecksum(data, 2, checksum)) {
odtulumbedder 0:062188c0bb61 120 reset();
odtulumbedder 0:062188c0bb61 121 return 1;
odtulumbedder 0:062188c0bb61 122 }
odtulumbedder 0:062188c0bb61 123 return result;
odtulumbedder 0:062188c0bb61 124 }
odtulumbedder 0:062188c0bb61 125
odtulumbedder 0:062188c0bb61 126 bool SHT21::crcChecksum(const uint8_t *data, uint8_t sz, uint8_t checksum) {
odtulumbedder 0:062188c0bb61 127 uint8_t crc = 0;
odtulumbedder 0:062188c0bb61 128
odtulumbedder 0:062188c0bb61 129 for (uint8_t i = 0; i < sz; ++i) {
odtulumbedder 0:062188c0bb61 130 crc ^= data[i];
odtulumbedder 0:062188c0bb61 131 for (uint8_t j /* bit index */ = 8; j > 0; --j) {
odtulumbedder 0:062188c0bb61 132 if (crc & 0x80)
odtulumbedder 0:062188c0bb61 133 crc = (crc << 1) ^ POLYNOMIAL;
odtulumbedder 0:062188c0bb61 134 else
odtulumbedder 0:062188c0bb61 135 crc = (crc << 1);
odtulumbedder 0:062188c0bb61 136 }
odtulumbedder 0:062188c0bb61 137 }
odtulumbedder 0:062188c0bb61 138
odtulumbedder 0:062188c0bb61 139 return crc == checksum;
odtulumbedder 0:062188c0bb61 140 }
odtulumbedder 0:062188c0bb61 141
odtulumbedder 0:062188c0bb61 142 SHT21 sht21(PB_9 /* I2C_SDA */, PB_8 /* I2C_SCL */);
odtulumbedder 0:062188c0bb61 143 Serial pc(USBTX, USBRX);
odtulumbedder 0:062188c0bb61 144
odtulumbedder 0:062188c0bb61 145 int main() {
odtulumbedder 0:062188c0bb61 146 while(1) {
odtulumbedder 0:062188c0bb61 147 pc.printf(
odtulumbedder 0:062188c0bb61 148 "%2.2f degC, %2.2f %%\n",
odtulumbedder 0:062188c0bb61 149 sht21.temperature(),
odtulumbedder 0:062188c0bb61 150 sht21.humidity());
odtulumbedder 0:062188c0bb61 151 wait(1);
odtulumbedder 0:062188c0bb61 152 }
odtulumbedder 0:062188c0bb61 153 }