Lieven Hollevoet / Si7005

Interface to a Silicon Labs Si7005 relative humidity sensor.

Dependents:   Si7005_example

Si7005.cpp@0:6fbf67893ca2, 2013-04-10 (annotated)

Committer:
LievenHollevoet
Date:
Wed Apr 10 08:43:56 2013 +0000
Revision:
0:6fbf67893ca2
First working version of a library to interface to a Silicon Labs Si7005 relative humidity sensor.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
LievenHollevoet 0:6fbf67893ca2 1 /* mbed Si7005 relative humidity sensor Library
LievenHollevoet 0:6fbf67893ca2 2 *
LievenHollevoet 0:6fbf67893ca2 3 * Copyright (c) 2013, Lieven Hollevoet (http://likatronix.be)
LievenHollevoet 0:6fbf67893ca2 4 *
LievenHollevoet 0:6fbf67893ca2 5 * Permission is hereby granted, free of charge, to any person obtaining a copy
LievenHollevoet 0:6fbf67893ca2 6 * of this software and associated documentation files (the "Software"), to deal
LievenHollevoet 0:6fbf67893ca2 7 * in the Software without restriction, including without limitation the rights
LievenHollevoet 0:6fbf67893ca2 8 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
LievenHollevoet 0:6fbf67893ca2 9 * copies of the Software, and to permit persons to whom the Software is
LievenHollevoet 0:6fbf67893ca2 10 * furnished to do so, subject to the following conditions:
LievenHollevoet 0:6fbf67893ca2 11 *
LievenHollevoet 0:6fbf67893ca2 12 * The above copyright notice and this permission notice shall be included in
LievenHollevoet 0:6fbf67893ca2 13 * all copies or substantial portions of the Software.
LievenHollevoet 0:6fbf67893ca2 14 *
LievenHollevoet 0:6fbf67893ca2 15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
LievenHollevoet 0:6fbf67893ca2 16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
LievenHollevoet 0:6fbf67893ca2 17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
LievenHollevoet 0:6fbf67893ca2 18 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LievenHollevoet 0:6fbf67893ca2 19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
LievenHollevoet 0:6fbf67893ca2 20 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
LievenHollevoet 0:6fbf67893ca2 21 * THE SOFTWARE.
LievenHollevoet 0:6fbf67893ca2 22 */
LievenHollevoet 0:6fbf67893ca2 23
LievenHollevoet 0:6fbf67893ca2 24
LievenHollevoet 0:6fbf67893ca2 25 #include "Si7005.h"
LievenHollevoet 0:6fbf67893ca2 26 #include "mbed.h"
LievenHollevoet 0:6fbf67893ca2 27
LievenHollevoet 0:6fbf67893ca2 28 /*
LievenHollevoet 0:6fbf67893ca2 29 Constructor, pin names for I2C of the device
LievenHollevoet 0:6fbf67893ca2 30 */
LievenHollevoet 0:6fbf67893ca2 31 Si7005::Si7005(PinName scl, PinName sda)
LievenHollevoet 0:6fbf67893ca2 32 : _i2c(scl, sda) {
LievenHollevoet 0:6fbf67893ca2 33
LievenHollevoet 0:6fbf67893ca2 34 _i2c.frequency(50000);
LievenHollevoet 0:6fbf67893ca2 35 _addr = 0x80;
LievenHollevoet 0:6fbf67893ca2 36 }
LievenHollevoet 0:6fbf67893ca2 37
LievenHollevoet 0:6fbf67893ca2 38
LievenHollevoet 0:6fbf67893ca2 39 int Si7005::readID(void) {
LievenHollevoet 0:6fbf67893ca2 40 int data;
LievenHollevoet 0:6fbf67893ca2 41
LievenHollevoet 0:6fbf67893ca2 42 data = _read(SI7005_REG_ID);
LievenHollevoet 0:6fbf67893ca2 43
LievenHollevoet 0:6fbf67893ca2 44 return data;
LievenHollevoet 0:6fbf67893ca2 45
LievenHollevoet 0:6fbf67893ca2 46 }
LievenHollevoet 0:6fbf67893ca2 47
LievenHollevoet 0:6fbf67893ca2 48 void Si7005::startMeasurement(char type) {
LievenHollevoet 0:6fbf67893ca2 49 char command;
LievenHollevoet 0:6fbf67893ca2 50
LievenHollevoet 0:6fbf67893ca2 51 switch (type) {
LievenHollevoet 0:6fbf67893ca2 52 case SI7005_RH:
LievenHollevoet 0:6fbf67893ca2 53 command = 0x01; // Start relative humidity measurement
LievenHollevoet 0:6fbf67893ca2 54 break;
LievenHollevoet 0:6fbf67893ca2 55 case SI7005_T:
LievenHollevoet 0:6fbf67893ca2 56 command = 0x11; // Start temperature measurement
LievenHollevoet 0:6fbf67893ca2 57 break;
LievenHollevoet 0:6fbf67893ca2 58 default:
LievenHollevoet 0:6fbf67893ca2 59 return;
LievenHollevoet 0:6fbf67893ca2 60 }
LievenHollevoet 0:6fbf67893ca2 61
LievenHollevoet 0:6fbf67893ca2 62 _write(SI7005_REG_CONFIG, command);
LievenHollevoet 0:6fbf67893ca2 63
LievenHollevoet 0:6fbf67893ca2 64 return;
LievenHollevoet 0:6fbf67893ca2 65 }
LievenHollevoet 0:6fbf67893ca2 66
LievenHollevoet 0:6fbf67893ca2 67 bool Si7005::conversionDone(void) {
LievenHollevoet 0:6fbf67893ca2 68 int result;
LievenHollevoet 0:6fbf67893ca2 69 result = _read(SI7005_REG_STATUS);
LievenHollevoet 0:6fbf67893ca2 70
LievenHollevoet 0:6fbf67893ca2 71 if (result == 0) {
LievenHollevoet 0:6fbf67893ca2 72 return true;
LievenHollevoet 0:6fbf67893ca2 73 } else {
LievenHollevoet 0:6fbf67893ca2 74 return false;
LievenHollevoet 0:6fbf67893ca2 75 }
LievenHollevoet 0:6fbf67893ca2 76
LievenHollevoet 0:6fbf67893ca2 77 }
LievenHollevoet 0:6fbf67893ca2 78
LievenHollevoet 0:6fbf67893ca2 79 int Si7005::readResult(char type) {
LievenHollevoet 0:6fbf67893ca2 80 int result;
LievenHollevoet 0:6fbf67893ca2 81 float f_res;
LievenHollevoet 0:6fbf67893ca2 82 float f_lin;
LievenHollevoet 0:6fbf67893ca2 83
LievenHollevoet 0:6fbf67893ca2 84 result = _read_int(SI7005_REG_DATAH);
LievenHollevoet 0:6fbf67893ca2 85
LievenHollevoet 0:6fbf67893ca2 86 switch (type) {
LievenHollevoet 0:6fbf67893ca2 87 case SI7005_RH:
LievenHollevoet 0:6fbf67893ca2 88 // Keep upper 12 bits
LievenHollevoet 0:6fbf67893ca2 89 result = result >> 4;
LievenHollevoet 0:6fbf67893ca2 90 // Calculate %
LievenHollevoet 0:6fbf67893ca2 91 f_res = ((float)result / 16) - 24;
LievenHollevoet 0:6fbf67893ca2 92 // Linearize
LievenHollevoet 0:6fbf67893ca2 93 f_lin = f_res - ((f_res * f_res) * - 0.00393 + f_res * 0.4008 - 4.7844 );
LievenHollevoet 0:6fbf67893ca2 94 return (int)f_lin;
LievenHollevoet 0:6fbf67893ca2 95 case SI7005_T:
LievenHollevoet 0:6fbf67893ca2 96 // Keep upper 14 bits
LievenHollevoet 0:6fbf67893ca2 97 result = result >> 2;
LievenHollevoet 0:6fbf67893ca2 98 // Calculate %
LievenHollevoet 0:6fbf67893ca2 99 result = (result / 32) - 50;
LievenHollevoet 0:6fbf67893ca2 100 return result;
LievenHollevoet 0:6fbf67893ca2 101 default:
LievenHollevoet 0:6fbf67893ca2 102 return -1;
LievenHollevoet 0:6fbf67893ca2 103 }
LievenHollevoet 0:6fbf67893ca2 104 }
LievenHollevoet 0:6fbf67893ca2 105 // private functions for low level IO
LievenHollevoet 0:6fbf67893ca2 106 // The Si7005 needs a restart bit when doing read accesses
LievenHollevoet 0:6fbf67893ca2 107
LievenHollevoet 0:6fbf67893ca2 108 void Si7005::_write(int reg, int data) {
LievenHollevoet 0:6fbf67893ca2 109 char args[2];
LievenHollevoet 0:6fbf67893ca2 110 args[0] = reg;
LievenHollevoet 0:6fbf67893ca2 111 args[1] = data;
LievenHollevoet 0:6fbf67893ca2 112 _i2c.write(_addr, args,2);
LievenHollevoet 0:6fbf67893ca2 113 }
LievenHollevoet 0:6fbf67893ca2 114
LievenHollevoet 0:6fbf67893ca2 115 int Si7005::_read(int reg) {
LievenHollevoet 0:6fbf67893ca2 116 char args[2];
LievenHollevoet 0:6fbf67893ca2 117 args[0] = reg;
LievenHollevoet 0:6fbf67893ca2 118 _i2c.write(_addr, args, 1, true); // No stop condition here
LievenHollevoet 0:6fbf67893ca2 119 _i2c.read(_addr, args, 1, true); // And a restart condition here
LievenHollevoet 0:6fbf67893ca2 120 _i2c.stop();
LievenHollevoet 0:6fbf67893ca2 121 return(args[0]);
LievenHollevoet 0:6fbf67893ca2 122 }
LievenHollevoet 0:6fbf67893ca2 123
LievenHollevoet 0:6fbf67893ca2 124 int Si7005::_read_int(int reg) {
LievenHollevoet 0:6fbf67893ca2 125 char data[2];
LievenHollevoet 0:6fbf67893ca2 126 data[0] = reg;
LievenHollevoet 0:6fbf67893ca2 127 _i2c.write(_addr, data, 1, true); // No stop condition here
LievenHollevoet 0:6fbf67893ca2 128 _i2c.read(_addr, data, 2, true); // And a restart condition here
LievenHollevoet 0:6fbf67893ca2 129 _i2c.stop();
LievenHollevoet 0:6fbf67893ca2 130
LievenHollevoet 0:6fbf67893ca2 131 // Data is read out MSB first
LievenHollevoet 0:6fbf67893ca2 132
LievenHollevoet 0:6fbf67893ca2 133 return ((data[0] << 8) + data[1]);
LievenHollevoet 0:6fbf67893ca2 134
LievenHollevoet 0:6fbf67893ca2 135 }
LievenHollevoet 0:6fbf67893ca2 136