Diff: AM2321.cpp

Revision:

0:d1c0dbf5e5a6

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/AM2321.cpp	Tue May 06 10:21:11 2014 +0000
@@ -0,0 +1,116 @@
+/*
+ *  AM2321 (Aosong Guangzhou Electronics)
+ *  Temperature and Humidity Sensor mbed library
+ * 
+ *  Copyright (c) 2014 tomozh <tomozh@gmail.com>
+ *  
+ *  This software is released under the MIT License.
+ *  http://opensource.org/licenses/mit-license.php
+ *
+ *  Last update : 2014/05/06
+ */
+
+#include "mbed.h"
+#include "AM2321.h"
+
+const int AM2321_I2C_ADDR = 0xB8;
+
+AM2321::AM2321(PinName sda, PinName scl)
+: _i2c(sda, scl)
+{
+    _result.temperature = 0.0f;
+    _result.humidity    = 0.0f;        
+}
+
+float AM2321::getLogicalValue(uint16_t regVal) const
+{
+    if(regVal & 0x8000)
+    {
+        regVal &= ~0x8000;
+        return (float)regVal / -10.0;
+    }
+    else
+    {
+        return (float)regVal / 10.0;    
+    }
+}
+
+uint16_t AM2321::calcCRC16(const uint8_t* src, int len) const
+{
+    uint16_t crc = 0xFFFF;
+
+    while(len--)
+    {
+        crc ^= *(src++);
+        
+        for(uint8_t i = 0; i < 8; i++)
+        {
+            if(crc & 0x01)
+            {
+                crc >>= 1;
+                crc ^= 0xA001;
+            }
+            else
+            {
+                crc >>= 1;
+            }
+        }
+    }
+    
+    return crc; 
+}
+
+bool AM2321::poll(void)
+{
+    bool    success = false;
+    uint8_t data[8];
+    
+    const static uint8_t READ_REGISTER_CMD[] = {
+           0x03     // Read register command
+         , 0x00     // start addrress
+         , 0x04     // read length
+          };
+
+    // wakeup
+    _i2c.write(AM2321_I2C_ADDR, NULL, 0);
+
+    // read data
+    _i2c.write(AM2321_I2C_ADDR, (char*)READ_REGISTER_CMD, 3);
+    wait_us(1600);
+
+    if(_i2c.read(AM2321_I2C_ADDR, (char*)data, 8) == 0)
+    {
+        uint8_t  cmd     = data[0];
+        uint8_t  dataLen = data[1];
+        uint16_t humiVal = (data[2] * 256) + data[3];
+        uint16_t tempVal = (data[4] * 256) + data[5];
+        uint16_t recvCRC = data[6] + (data[7] * 256);
+        uint16_t chkCRC  = calcCRC16(&data[0], 6);
+
+        if(dataLen == 4)
+        {
+            if(recvCRC == chkCRC)
+            {
+                if(cmd == 0x03)
+                {
+                    _result.temperature = getLogicalValue(tempVal);
+                    _result.humidity    = getLogicalValue(humiVal);
+
+                    success = true;
+                }
+            }
+        }
+    }
+    
+    return success;
+}
+
+float AM2321::getTemperature(void) const
+{
+    return _result.temperature;
+}
+
+float AM2321::getHumidity(void) const
+{
+    return _result.humidity;
+}