Diff: SHT1x.cpp

Revision:

0:ad72ec3d85e8

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/SHT1x.cpp	Thu Jun 21 03:56:43 2012 +0000
@@ -0,0 +1,117 @@
+/*
+ * mbed library to use a SENSIRION SHT1x/SHT7x sensor
+ * Copyright (c) 2011 Hiroshi Suga
+ * Released under the MIT License: http://mbed.org/license/mit
+ */
+ 
+/** @file
+ * @brief mbed library to use a SENSIRION SHT1x/SHT7x sensor
+ * humidity/temperature sensor SHT11, SHT15, SHT71, SHT75 (SENSIRION) Ver.4
+ * interface: I2C digital
+ */
+
+#include "mbed.h"
+#include "SHT1x.h"
+
+enum SHT_cmd {
+    SHT_cmd_temperature = 0x03,
+    SHT_cmd_humidity = 0x05,
+    SHT_cmd_read_status = 0x07,
+    SHT_cmd_write_status = 0x06,
+    SHT_cmd_reset = 0x1e
+};
+
+SHT1x::SHT1x (PinName p_sda, PinName p_scl, SHT_acc p_acc, SHT_vdd p_vdd) : i2c(p_sda, p_scl) {
+    init(p_acc, p_vdd);
+}
+
+SHT1x::SHT1x (I2C& p_i2c, SHT_acc p_acc, SHT_vdd p_vdd) : i2c(p_i2c) {
+    init(p_acc, p_vdd);
+}
+
+float SHT1x::get_temperature() {
+    return temperature;
+}
+
+float SHT1x::get_humidity() {
+    return humidity;
+}
+
+void SHT1x::update () {
+    float t, rhl, rht;
+    unsigned short sot, sorh;
+
+    sot = twi_readshort(SHT_cmd_temperature, (accuracy == SHT_low ? 80 : 320));
+    sorh = twi_readshort(SHT_cmd_humidity, (accuracy == SHT_low ? 20 : 80));
+    if (sot == 0xffff || sorh == 0xffff) return;
+
+    if (accuracy == SHT_low) {
+        sot &= 0x0fff; // 12bit
+        sorh &= 0x00ff; // 8bit
+    } else {
+        sot &= 0x3fff; // 14bit
+        sorh &= 0x0fff; // 12bit
+    }    
+
+    t = d1 + d2 * (float)sot;
+    temperature = t;
+
+    rhl = c1 + c2 * (float)sorh + c3 * (float)(sorh * sorh);
+    rht = (t - 25.0) * (t1 + t2 * (float)sorh) + rhl;
+    if (rht > 99.0) rht = 100.0;
+    humidity = rht;
+}
+
+void SHT1x::init (SHT_acc p_acc, SHT_vdd p_vdd) {
+
+    humidity = 0;
+    temperature = 0;
+
+    if (p_vdd == SHT_3V3) {
+        d1 = -39.66; // 3.3V
+    } else {
+        d1 = -40.1; // 5V
+    }
+
+    accuracy = p_acc;
+    if (accuracy == SHT_low) {
+        d2 = 0.04;
+        c1 = -2.0468; c2 = 0.5872; c3 = -4.0845/10000.0;
+        t1 = 0.01; t2 = 0.00128;
+        twi_writechar(SHT_cmd_write_status, 1);
+    } else {
+        d2 = 0.01;
+        c1 = -2.0468; c2 = 0.0367; c3 = -1.5955/1000000.0;
+        t1 = 0.01; t2 = 0.00008;
+        twi_writechar(SHT_cmd_write_status, 0);
+    }    
+}
+
+unsigned short SHT1x::twi_readshort (int addr, int wait) {
+    unsigned short i;
+
+    i2c.start();
+    i2c.stop();
+
+    i2c.start();
+    i2c.write(addr);
+    wait_ms(wait);
+
+    i = i2c.read(1) << 8;
+    i |= i2c.read(1);
+    i2c.read(0);
+    i2c.stop();
+
+    return i;
+}
+
+void SHT1x::twi_writechar (int addr, int dat) {
+
+    i2c.start();
+    i2c.stop();
+
+    i2c.start();
+    i2c.write(addr);
+    i2c.write(dat);
+    i2c.stop();
+}