Diff: Sht31.cpp

Revision:

0:86f8e66e04fc

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Sht31.cpp	Tue Jun 08 10:37:36 2021 +0000
@@ -0,0 +1,112 @@
+/***************************************************
+  This is a library for the SHT31 Digital Humidity & Temp Sht31
+
+  Designed specifically to work with the SHT31 Digital Sht31 from Adafruit
+  ----> https://www.adafruit.com/products/2857
+
+  These displays use I2C to communicate, 2 pins are required to
+  interface
+  Adafruit invests time and resources providing this open source code,
+  please support Adafruit and open-source hardware by purchasing
+  products from Adafruit!
+
+  Written by Limor Fried/Ladyada for Adafruit Industries.
+  BSD license, all text above must be included in any redistribution
+ ****************************************************/
+
+#include "Sht31.h"
+#include "mbed.h"
+
+Sht31::Sht31(PinName sda, PinName scl) : _i2c(sda, scl) {
+    _i2caddr = (0x44 << 1);
+    reset();
+    readStatus();
+}
+
+int Sht31::readTemperature(void) {
+    if (! readTempHum()) return NAN;
+    return temp;
+}
+
+int Sht31::readHumidity(void) {
+    if (! readTempHum()) return NAN;
+    return humidity;
+}
+
+void Sht31::reset(void) {
+    writeCommand(SHT31_SOFTRESET);
+    wait_ms(10);
+}
+
+uint16_t Sht31::readStatus(void) {
+    writeCommand(SHT31_READSTATUS);
+    char val[1];
+    _i2c.read(_i2caddr, val, 1);
+    uint16_t stat = val[0];
+    stat <<= 8;
+    _i2c.read(_i2caddr, val, 1);
+    stat |= val[0];
+    // printf("0x%X\r\n", stat);
+    return stat;
+}
+
+void Sht31::writeCommand(uint16_t cmd) {
+    char buf[2];
+    buf[0] = (cmd >> 8);
+    buf[1] = (cmd & 0xFF);
+    _i2c.write(_i2caddr, buf, 2);
+}
+
+bool Sht31::readTempHum(void) {
+    char readbuffer[6];
+
+    writeCommand(SHT31_MEAS_HIGHREP);
+
+    wait_ms(500);
+    _i2c.read(_i2caddr, readbuffer, 6);
+    
+    uint16_t ST, SRH;
+    ST = readbuffer[0];
+    ST <<= 8;
+    ST |= readbuffer[1];
+
+    if (readbuffer[2] != crc8((uint8_t *) readbuffer, 2)) {
+        return false;
+    }
+
+    SRH = readbuffer[3];
+    SRH <<= 8;
+    SRH |= readbuffer[4];
+
+    if (readbuffer[5] != crc8((uint8_t *) readbuffer+3, 2)) {
+        return false;
+    }
+
+    double stemp = ST;
+    stemp *= 175;
+    stemp /= 0xffff;
+    stemp = -45 + stemp;
+    temp = stemp;
+
+    double shum = SRH;
+    shum *= 100;
+    shum /= 0xFFFF;
+
+    humidity = shum;
+
+    return true;
+}
+
+uint8_t Sht31::crc8(const uint8_t *data, int len) {
+    const uint8_t POLYNOMIAL(0x31);
+    uint8_t crc(0xFF);
+
+    for ( int j = len; j; --j ) {
+        crc ^= *data++;
+
+        for ( int i = 8; i; --i ) {
+            crc = (crc & 0x80) ? (crc << 1) ^ POLYNOMIAL : (crc << 1);
+        }
+    }
+    return crc;
+}