Revision 0:6fbf67893ca2, committed 2013-04-10

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

--- /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]);
+
+}
+

--- /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
+