Initial version of library

DISTRIBUTION

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+Copyright 2009 Jonathan Oxer <[email protected]>
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+http://www.gnu.org/licenses/

README

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+SHT1x
+=====
+
+Copyright 2009 Jonathan Oxer <[email protected]>
+www.practicalarduino.com
+
+Provides a simple interface to the SHT1x series (SHT10, SHT11, SHT15)
+temperature / humidity sensors from Sensirion (www.sensirion.com).
+These sensors use a "2-wire" communications buss that is similar to I2C
+and can co-exist on the same physical wire as I2C devices, but is not
+directly interoperable with it.

SHT1x.cpp

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+/**
+ * SHT1x Library
+ *
+ * Copyright 2009 Jonathan Oxer <[email protected]> / <www.practicalarduino.com>
+ * Based on previous work by:
+ *    Maurice Ribble: <www.glacialwanderer.com/hobbyrobotics/?p=5>
+ *    Wayne ?: <ragingreality.blogspot.com/2008/01/ardunio-and-sht15.html>
+ *
+ * Manages communication with SHT1x series (SHT10, SHT11, SHT15)
+ * temperature / humidity sensors from Sensirion (www.sensirion.com).
+ */
+#include "WProgram.h"
+#include "SHT1x.h"
+
+SHT1x::SHT1x(int dataPin, int clockPin)
+{
+  _dataPin = dataPin;
+  _clockPin = clockPin;
+}
+
+
+/* ================  Public methods ================ */
+
+/**
+ * Reads the current temperature in degrees Celsius
+ */
+float SHT1x::readTemperatureC()
+{
+  int _val;                // Raw value returned from sensor
+  float _temperature;      // Temperature derived from raw value
+
+  // Conversion coefficients from SHT15 datasheet
+  const float D1 = -40.0;  // for 14 Bit @ 5V
+  const float D2 =   0.01; // for 14 Bit DEGC
+
+  // Fetch raw value
+  _val = readTemperatureRaw();
+
+  // Convert raw value to degrees Celsius
+  _temperature = (_val * D2) + D1;
+
+  return (_temperature);
+}
+
+/**
+ * Reads the current temperature in degrees Fahrenheit
+ */
+float SHT1x::readTemperatureF()
+{
+  int _val;                 // Raw value returned from sensor
+  float _temperature;       // Temperature derived from raw value
+
+  // Conversion coefficients from SHT15 datasheet
+  const float D1 = -40.0;   // for 14 Bit @ 5V
+  const float D2 =   0.018; // for 14 Bit DEGC
+
+  // Fetch raw value
+  _val = readTemperatureRaw();
+
+  // Convert raw value to degrees Celsius
+  _temperature = (_val * D2) + D1;
+
+  return (_temperature);
+}
+
+/**
+ * Reads current temperature-corrected relative humidity
+ */
+float SHT1x::readHumidity()
+{
+  int _val;                    // Raw humidity value returned from sensor
+  float _linearHumidity;       // Humidity with linear correction applied
+  float _correctedHumidity;    // Temperature-corrected humidity
+  float _temperature;          // Raw temperature value
+
+  // Conversion coefficients from SHT15 datasheet
+  const float C1 = -4.0;       // for 12 Bit
+  const float C2 =  0.0405;    // for 12 Bit
+  const float C3 = -0.0000028; // for 12 Bit
+  const float T1 =  0.01;      // for 14 Bit @ 5V
+  const float T2 =  0.00008;   // for 14 Bit @ 5V
+
+  // Command to send to the SHT1x to request humidity
+  int _gHumidCmd = 0b00000101;
+
+  // Fetch the value from the sensor
+  sendCommandSHT(_gHumidCmd, _dataPin, _clockPin);
+  waitForResultSHT(_dataPin);
+  _val = getData16SHT(_dataPin, _clockPin);
+  skipCrcSHT(_dataPin, _clockPin);
+
+  // Apply linear conversion to raw value
+  _linearHumidity = C1 + C2 * _val + C3 * _val * _val;
+
+  // Get current temperature for humidity correction
+  _temperature = readTemperatureC();
+
+  // Correct humidity value for current temperature
+  _correctedHumidity = _temperature * (T1 + T2 * _val) + _linearHumidity;
+
+  return (_correctedHumidity);
+}
+
+
+/* ================  Private methods ================ */
+
+/**
+ * Reads the current raw temperature value
+ */
+float SHT1x::readTemperatureRaw()
+{
+  int _val;
+
+  // Command to send to the SHT1x to request Temperature
+  int _gTempCmd  = 0b00000011;
+
+  sendCommandSHT(_gTempCmd, _dataPin, _clockPin);
+  waitForResultSHT(_dataPin);
+  _val = getData16SHT(_dataPin, _clockPin);
+  skipCrcSHT(_dataPin, _clockPin);
+
+  return (_val);
+}
+
+/**
+ */
+int SHT1x::shiftIn(int _dataPin, int _clockPin, int _numBits)
+{
+  int ret = 0;
+  int i;
+
+  for (i=0; i<_numBits; ++i)
+  {
+     digitalWrite(_clockPin, HIGH);
+     delay(10);  // I don't know why I need this, but without it I don't get my 8 lsb of temp
+     ret = ret*2 + digitalRead(_dataPin);
+     digitalWrite(_clockPin, LOW);
+  }
+
+  return(ret);
+}
+
+/**
+ */
+void SHT1x::sendCommandSHT(int _command, int _dataPin, int _clockPin)
+{
+  int ack;
+
+  // Transmission Start
+  pinMode(_dataPin, OUTPUT);
+  pinMode(_clockPin, OUTPUT);
+  digitalWrite(_dataPin, HIGH);
+  digitalWrite(_clockPin, HIGH);
+  digitalWrite(_dataPin, LOW);
+  digitalWrite(_clockPin, LOW);
+  digitalWrite(_clockPin, HIGH);
+  digitalWrite(_dataPin, HIGH);
+  digitalWrite(_clockPin, LOW);
+
+  // The command (3 msb are address and must be 000, and last 5 bits are command)
+  shiftOut(_dataPin, _clockPin, MSBFIRST, _command);
+
+  // Verify we get the correct ack
+  digitalWrite(_clockPin, HIGH);
+  pinMode(_dataPin, INPUT);
+  ack = digitalRead(_dataPin);
+  if (ack != LOW) {
+    //Serial.println("Ack Error 0");
+  }
+  digitalWrite(_clockPin, LOW);
+  ack = digitalRead(_dataPin);
+  if (ack != HIGH) {
+    //Serial.println("Ack Error 1");
+  }
+}
+
+/**
+ */
+void SHT1x::waitForResultSHT(int _dataPin)
+{
+  int i;
+  int ack;
+
+  pinMode(_dataPin, INPUT);
+
+  for(i= 0; i < 100; ++i)
+  {
+    delay(10);
+    ack = digitalRead(_dataPin);
+
+    if (ack == LOW) {
+      break;
+    }
+  }
+
+  if (ack == HIGH) {
+    //Serial.println("Ack Error 2"); // Can't do serial stuff here, need another way of reporting errors
+  }
+}
+
+/**
+ */
+int SHT1x::getData16SHT(int _dataPin, int _clockPin)
+{
+  int val;
+
+  // Get the most significant bits
+  pinMode(_dataPin, INPUT);
+  pinMode(_clockPin, OUTPUT);
+  val = shiftIn(_dataPin, _clockPin, 8);
+  val *= 256;
+
+  // Send the required ack
+  pinMode(_dataPin, OUTPUT);
+  digitalWrite(_dataPin, HIGH);
+  digitalWrite(_dataPin, LOW);
+  digitalWrite(_clockPin, HIGH);
+  digitalWrite(_clockPin, LOW);
+
+  // Get the least significant bits
+  pinMode(_dataPin, INPUT);
+  val |= shiftIn(_dataPin, _clockPin, 8);
+
+  return val;
+}
+
+/**
+ */
+void SHT1x::skipCrcSHT(int _dataPin, int _clockPin)
+{
+  // Skip acknowledge to end trans (no CRC)
+  pinMode(_dataPin, OUTPUT);
+  pinMode(_clockPin, OUTPUT);
+
+  digitalWrite(_dataPin, HIGH);
+  digitalWrite(_clockPin, HIGH);
+  digitalWrite(_clockPin, LOW);
+}

SHT1x.h

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+/**
+ * SHT1x Library
+ *
+ * Copyright 2009 Jonathan Oxer <[email protected]> / <www.practicalarduino.com>
+ * Based on previous work by:
+ *    Maurice Ribble: <www.glacialwanderer.com/hobbyrobotics/?p=5>
+ *    Wayne ?: <ragingreality.blogspot.com/2008/01/ardunio-and-sht15.html>
+ *
+ * Manages communication with SHT1x series (SHT10, SHT11, SHT15)
+ * temperature / humidity sensors from Sensirion (www.sensirion.com).
+ */
+#ifndef SHT1x_h
+#define SHT1x_h
+
+#include "WProgram.h"
+
+class SHT1x
+{
+  public:
+    SHT1x(int dataPin, int clockPin);
+    float readHumidity();
+    float readTemperatureC();
+    float readTemperatureF();
+  private:
+    int _dataPin;
+    int _clockPin;
+    int _numBits;
+    float readTemperatureRaw();
+    int shiftIn(int _dataPin, int _clockPin, int _numBits);
+    void sendCommandSHT(int _command, int _dataPin, int _clockPin);
+    void waitForResultSHT(int _dataPin);
+    int getData16SHT(int _dataPin, int _clockPin);
+    void skipCrcSHT(int _dataPin, int _clockPin);
+};
+
+#endif

examples/ReadSHT1xValues/ReadSHT1xValues.pde

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+/**
+ * ReadSHT1xValues
+ *
+ * Read temperature and humidity values from an SHT1x-series (SHT10,
+ * SHT11, SHT15) sensor.
+ *
+ * Copyright 2009 Jonathan Oxer <jon@oxer.com.au>
+ * www.practicalarduino.com
+ */
+
+#include <SHT1x.h>
+
+// Specify data and clock connections and instantiate SHT1x object
+#define dataPin  10
+#define clockPin 11
+SHT1x sht1x(dataPin, clockPin);
+
+void setup()
+{
+   Serial.begin(38400); // Open serial connection to report values to host
+   Serial.println("Starting up");
+}
+
+void loop()
+{
+  float temp_c;
+  float temp_f;
+  float humidity;
+
+  // Read values from the sensor
+  temp_c = sht1x.readTemperatureC();
+  temp_f = sht1x.readTemperatureF();
+  humidity = sht1x.readHumidity();
+
+  // Print the values to the serial port
+  Serial.print("Temperature: ");
+  Serial.print(temp_c, DEC);
+  Serial.print("C / ");
+  Serial.print(temp_f, DEC);
+  Serial.print("F. Humidity: ");
+  Serial.print(humidity);
+  Serial.println("%");
+
+  delay(2000);
+}