Interface to a Silicon Labs Si7005 relative humidity sensor.
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
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 |
--- /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 +