Interface to a Silicon Labs Si7005 relative humidity sensor.

Dependents:   Si7005_example

Files at this revision

API Documentation at this revision

Comitter:
LievenHollevoet
Date:
Wed Apr 10 08:43:56 2013 +0000
Commit message:
First working version of a library to interface to a Silicon Labs Si7005 relative humidity sensor.

Changed in this revision

Si7005.cpp Show annotated file Show diff for this revision Revisions of this file
Si7005.h Show annotated file Show diff for this revision Revisions of this file
diff -r 000000000000 -r 6fbf67893ca2 Si7005.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Si7005.cpp	Wed Apr 10 08:43:56 2013 +0000
@@ -0,0 +1,136 @@
+/* mbed Si7005 relative humidity sensor Library
+ *
+ * Copyright (c) 2013, Lieven Hollevoet (http://likatronix.be)
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+
+#include "Si7005.h"
+#include "mbed.h"
+
+/*
+ Constructor, pin names for I2C of the device
+ */
+Si7005::Si7005(PinName scl, PinName sda)
+        : _i2c(scl, sda) {
+
+    _i2c.frequency(50000);
+      _addr = 0x80;
+}
+
+
+int Si7005::readID(void) {
+    int data;
+
+    data = _read(SI7005_REG_ID);
+
+    return data;
+
+}
+
+void Si7005::startMeasurement(char type) {
+    char command;
+
+    switch (type) {
+    case SI7005_RH:
+        command = 0x01; // Start relative humidity measurement
+        break;
+    case SI7005_T:
+        command = 0x11; // Start temperature measurement
+        break;
+    default:
+        return;
+    }
+
+    _write(SI7005_REG_CONFIG, command);
+
+    return;
+}
+
+bool Si7005::conversionDone(void) {
+    int result;
+    result = _read(SI7005_REG_STATUS);
+
+    if (result == 0) {
+        return true;
+    } else {
+        return false;
+    }
+
+}
+
+int Si7005::readResult(char type) {
+    int result;
+    float f_res;
+    float f_lin;
+
+    result = _read_int(SI7005_REG_DATAH);
+
+    switch (type) {
+    case SI7005_RH:
+        // Keep upper 12 bits
+        result = result >> 4;
+        // Calculate %
+        f_res = ((float)result / 16) - 24;
+        // Linearize
+        f_lin = f_res - ((f_res * f_res) * - 0.00393 + f_res * 0.4008 - 4.7844 );
+        return (int)f_lin;
+    case SI7005_T:
+        // Keep upper 14 bits
+        result = result >> 2;
+        // Calculate %
+        result = (result / 32) - 50;
+        return result;
+    default:
+        return -1;
+    }
+}
+// private functions for low level IO
+// The Si7005 needs a restart bit when doing read accesses
+
+void Si7005::_write(int reg, int data) {
+    char args[2];
+    args[0] = reg;
+    args[1] = data;
+    _i2c.write(_addr, args,2);
+}
+
+int Si7005::_read(int reg) {
+    char args[2];
+    args[0] = reg;
+    _i2c.write(_addr, args, 1, true); // No stop condition here
+    _i2c.read(_addr, args, 1, true);  // And a restart condition here
+    _i2c.stop();
+    return(args[0]);
+}
+
+int Si7005::_read_int(int reg) {
+    char data[2];
+    data[0] = reg;
+    _i2c.write(_addr, data, 1, true); // No stop condition here
+    _i2c.read(_addr, data, 2, true);  // And a restart condition here
+    _i2c.stop();
+
+    // Data is read out MSB first
+
+    return ((data[0] << 8) + data[1]);
+
+}
+
diff -r 000000000000 -r 6fbf67893ca2 Si7005.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Si7005.h	Wed Apr 10 08:43:56 2013 +0000
@@ -0,0 +1,137 @@
+/* mbed Si7005 relative humidity sensor Library
+ *
+ * Copyright (c) 2013, Lieven Hollevoet (http://likatronix.be)
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef SI7005_H
+#define SI7005_H
+
+#include "mbed.h"
+
+/*
+ * register names
+ */
+
+#define SI7005_REG_STATUS  0
+#define SI7005_REG_DATAH   1
+#define SI7005_REG_DATAL   2
+#define SI7005_REG_CONFIG  3
+#define SI7005_REG_ID     17
+
+/*
+ * measurement types
+ */
+
+#define SI7005_RH 0
+#define SI7005_T  1
+
+/** Class to interface to a Silicon Labs Si7005 relative humidity sensor.
+ *
+ * Example:
+ * @code
+ * #include "mbed.h"
+ * #include "Si7005.h"
+ *
+ * Si7005 rh(p28, p27);         // sda, scl
+ * DigitalOut rh_cs_n(p26);     // Chip select signal
+ * Serial uart(USBTX, USBRX);   // tx, rx
+ 
+ * int main() {
+ *
+ *     // Enable RH sensor
+ *     rh_cs_n = 0;
+ *     // Let it startup!
+ *     wait(0.05);
+ *
+ *     char id;
+ *     id = rh.readID();
+ *     uart.printf("Sensor type: %02X\n", id);
+ 
+ *     // Relative humidity measurement
+ *     rh.startMeasurement(SI7005_RH);
+ *     while (!rh.conversionDone()) {
+ *             wait(0.01);
+ *     }
+ *     int measurement = rh.readResult(SI7005_RH);
+ *     uart.printf("RH = %i procent\n", measurement);
+ *
+ *       // Start temperature measurement
+ *       rh.startMeasurement(SI7005_T);
+ *       while (!rh.conversionDone()){
+ *         wait (0.01);
+ *       }
+ *       measurement = rh.readResult(SI7005_T);
+ *       uart.printf("Temp = %i degrees C\n", measurement);
+ *
+ *     // Disable the sensor
+ *     rh_cs_n = 1;
+ *
+ * }
+ * @endcode
+ */
+class Si7005 {
+
+public:
+
+    /** Creates the sensor interface instance
+     * @param sda I2C data pin
+     * @param scl I2C clock pin
+     */
+    Si7005(PinName sda, PinName scl);
+
+    /** Read the chip ID
+     * @returns The chip ID register contents. Should be in the format 0x5y for a Si7005 sensor where 'y' is the chip revision.
+     */
+    int readID (void);
+
+    /** Start a measurement for relative humidity or temperature
+     * Initiate a measurement. The type can be either SI7005_RH for a relative humidity measurement or SI7005_T for a temperature measurement.
+     * This function starts the conversion in the sensor. Before reading out the
+     * result, ensure the conversion is done by calling conversionDone().
+     * @param type Either SI7005_RH for humidity measurement or SI7005_T for temperature
+     */
+    void startMeasurement (char type);
+
+    /** Checks if the measurement is done.
+     * Reports true if the conversion is finished. This is detected by reading the DONE bit in the STATUS register of the sensor.
+     * @returns true if the conversion is done
+     */
+    bool conversionDone (void);
+
+    /** Reads the measurement result.
+     * @param type Either SI7005_RH for humidity measurement or SI7005_T for temperature
+     * @returns The measurement result as specified in the datasheet, a 12-bit value for the relative humidity measurement and a 14-bit value for a temperature measurement.
+     */
+    int readResult (char type);
+
+protected:
+
+    void _write(int reg, int data);
+    int _read(int reg);
+    int _read_int(int reg);
+    int _addr;
+    I2C _i2c;
+
+};
+
+
+#endif
+