added decoder for the Dragino LHT52.

Dragino/LHT52/decoder.js

@@ -0,0 +1,84 @@
+/* 
+* Payload decoder for the Dragino LHT52 temperature sensor
+*/
+
+function Decoder(bytes, port) {
+
+    // The sensor supports multiple different payload types sent on predetermined ports.
+    if (port == 2) {
+        return decodeSensorData(bytes);
+    } else if (port == 5) {
+        return decodeDeviceStatus(bytes);
+    }
+
+    var output = {};
+    output.port = port;
+    return output;
+}
+
+function str_pad(byte){
+    var zero = '0';
+    var hex= byte.toString(16);    
+    var tmp  = 2-hex.length;
+    return zero.substr(0,tmp) + hex;
+}
+
+/**
+ * Decode sensor data
+ */
+function decodeSensorData(bytes) {
+    // Temperature
+    temperature = (((bytes[0] & 0xFF) << 8) | (bytes[1] & 0xFF)) / 100;
+
+    // Humidity
+    humidity = (((bytes[2] & 0xFF) << 8) | (bytes[3] & 0xFF)) / 10;
+
+    // External temperature
+    externalTemperature = (((bytes[4] & 0xFF) << 8) | (bytes[5] & 0xFF)) / 100;
+
+    // Ext
+    ext = bytes[6]; 
+
+    // Timestamp
+    timestamp = (bytes[7]<<24 | bytes[8]<<16 | bytes[9]<<8 | bytes[10]);
+
+    // Decoder output
+    var output = {};
+    output.temperature = temperature;
+    output.humidity = humidity;
+    output.external_temperature = externalTemperature;
+    output.ext = ext;
+    output.timestamp = timestamp;
+
+    return output;
+}
+
+/**
+ * Decode device status
+ */
+function decodeDeviceStatus(bytes) {
+    // Sensor Model
+    sensorModel = bytes[0];
+
+    // Firmware Version
+    firmwareVersion = str_pad((bytes[1]<<8)|bytes[2]);
+
+    // Frequency Band
+    frequencyBand = bytes[3];
+
+    // Sub band
+    subBand = bytes[4];
+
+    // Battery Voltage (in V)
+    batVoltage = (bytes[5]<<8|bytes[6]) / 1000;
+
+    // Decoder output
+    var output = {};
+    output.sensor_model = sensorModel;
+    output.firmware_version = firmwareVersion;
+    output.frequency_band = frequencyBand;
+    output.sub_band = subBand;
+    output.battery_voltage = batVoltage;
+
+    return output;
+}