implemented dht22 reading

updated readme
added example

Author: depuits

README.md

@@ -1,9 +1,57 @@
 # pigpio-dht
+
 Dht22 control using node.js and pigpio.
 
 ## Installation
+
 1. Install [pigpio C library](https://github.com/joan2937/pigpio).
-2. Install module dependencies: `npm i pigpio-dht`.
+2. Install module: `npm i pigpio-dht`.
+
+## Usage
+
+```javascript
+const dht = require('dht');
+
+const dataPin = 5;
+const sensor = dht(dataPin);
+
+setInterval(() => { 
+	sensor.read();
+}, 2500); // the sensor can only be red every 2 seconds
+
+sensor.on('result', data => {
+	console.log(`temp: ${data.temperature}°c`); 
+	console.log(`rhum: ${data.humidity}%`); 
+});
+
+sensor.on('badChecksum', () => {
+	console.log('checksum failed');
+});
+```
+
+### Events
+
+#### start
+
+Emitted when starting to read a value.
+
+#### end
+
+Emitted when the reading stops. This because it was complete, an error occured or anything else.
+
+#### result
+
+- result object containing temperature and humidity
+Emitted when the reading was completed successful.
+
+#### badChecksum
+
+Emitted when finished reading but the checksum was invalid.
+
+## Built With
+
+* [pigpio](https://github.com/fivdi/pigpio) - Gpio wrapper for nodejs
+
+## Versioning
 
-## usage
-TODO
+We use [SemVer](http://semver.org/) for versioning. For the versions available, see the [tags on this repository](https://github.com/your/project/tags).

examples/simpleRead.js

@@ -0,0 +1,17 @@
+const dht = require('../');
+
+const dataPin = 5;
+const sensor = dht(dataPin);
+
+setInterval(() => { 
+	sensor.read();
+}, 2500); // the sensor can only be red every 2 seconds
+
+sensor.on('result', data => {
+	console.log(`temp: ${data.temperature}°c`); 
+	console.log(`rhum: ${data.humidity}%`); 
+});
+
+sensor.on('badChecksum', () => {
+	console.log('checksum failed');
+});

index.js

@@ -1,28 +1,124 @@
 'use strict';
 const Gpio = require('pigpio').Gpio;
+const eventEmitter = require('events').EventEmitter;
 
 module.exports = function(pin, type) {
+	const dht = Object.create(new eventEmitter());
 	const gpio = new Gpio(pin, { mode: Gpio.OUTPUT, pullUpDown: Gpio.PUD_OFF };
 
-	gpio.trigger(80, 0);
+	dht.reading = false;
 
-	gpio.enableAlert();
-	gpio.disableAlert();
+	var lastHighTick = 0;
+	var bits = 0;
+
+	var rhumHigh = 0;
+	var rhumLow = 0;
+	var tempHigh = 0;
+	var tempLow = 0;
+	var checksum = 0;
+
+	function startReading() {
+		if (dht.reading) {
+			// cancel out if we are already reading
+			return false;
+		}
+		dht.emmit('start');
+		// Trigger a new relative humidity and temperature reading.
+		// write low for 18 ms
+		gpio.digitalWrite(0);
+		// after that let the line go high and start reading
+		setTimeout(() => { 
+			// reset all values
+			bits = -2; // initialized at -2 because the first 2 lows are the ack
+			rhumHigh = 0;
+			rhumLow = 0;
+			tempHigh = 0;
+			tempLow = 0;
+			checksum = 0;
+
+			// start reading input
+			gpio.mode(Gpio.INPUT);
+			gpio.enableAlert();
+		}, 18);
+
+		return true;
+	}
+	function endReading() {
+		dht.reading = false;
+		gpio.disableAlert();
+		gpio.mode(Gpio.OUTPUT);
+		dht.emmit('end');
+	}
 
 	gpio.on('alert', (level, tick) => {
-		//TODO communication logic goes here
-		var startTick = 0xffffffff; // 2^32-1 or 4294967295, the max unsigned 32 bit integer
-		var endTick = 1;
-		console.log((endTick >> 0) - (startTick >> 0)); // prints 2 which is what we want
+		// Accumulate the 40 data bits.  Format into 5 bytes, humidity high,
+		// humidity low, temperature high, temperature low, checksum.
+
+		// bits are only accumulated on the low level
+		if (level == 0) {
+			let diff = (tick >> 0) - (lastHighTick >> 0);
+			
+			// Edge length determines if bit is 1 or 0.
+			let val = 0;
+			// low bit is between 26 and 28 µs
+			// high bit is 70 µs
+			// So we check on the value in between to avoid small differences
+			if (diff >= 50) {
+				val = 1;
+				if (diff >= 200) { // Bad bit?
+					checksum = 256; // Force bad checksum.
+				}
+			}
+
+			if (bits < 0) {
+				// header bits
+				// we don't need to do anything with these
+			} else if (bits < 8) {
+				// in humidity high byte
+				rhumHigh = (rhumHigh << 1) + val;				
+			} else if (bits < 16) {
+				// in humidity low byte
+				rhumLow = (rhumLow << 1) + val;				
+			} else if (bits < 24) {
+				// in temp high byte
+				tempHigh = (tempHigh << 1) + val;				
+			} else if (bits < 32) {
+				// in temp low byte
+				tempLow = (tempLow << 1) + val;
+			} else {
+				// In checksum byte.
+				checksum  = (checksum << 1)  + val;
+
+				if (bits == 39) {
+					// 40th bit received.
+					endReading();
+
+					let total = rhumHigh + rhumLow + tempHigh + tempLow;
+
+					// Is checksum ok?
+					if ((total & 255) == checksum) {
+						let rhum = ((rhumHigh << 8) + rhumLow) * 0.1;
+
+						// check the temperature sign
+						let mult = (tempHigh & 128) ? -0.1 : 0.1;
+						tempHigh = tempHigh & 127; // strip the sign bit
+						let temp = ((tempHigh << 8) + tempLow) * mult;
+						
+						dht.emit('result', { temperature: temp, humidity: rhum });
+					} else {
+						dht.emmit('badChecksum');
+					}
+				}
+			}
+
+			++bits;
+		} else if (level == 1) {
+			lastHighTick = tick;
+		}
 	});
 
-	function trigger() {
-		//Trigger a new relative humidity and temperature reading.
-		
-		//TODO implement
-		/*self.pi.write(self.gpio, pigpio.LOW)
-		time.sleep(0.017) // 17 ms
-		self.pi.set_mode(self.gpio, pigpio.INPUT)
-		self.pi.set_watchdog(self.gpio, 200)*/
-	}
+	return Object.assign(dht, {
+		gpio, 
+		read: startReading
+	});
 };

package.json

@@ -1,7 +1,7 @@
 {
   "name": "pigpio-dht",
   "version": "1.0.0",
-  "description": "DHT implementation using node.js and pigpio.",
+  "description": "Dht22 control using node.js and pigpio.",
   "main": "index.js",
   "scripts": {
     "test": "echo \"Error: no test specified\" && exit 1"
@@ -13,17 +13,16 @@
   "keywords": [
     "DHT",
     "DHT22",
-    "pigpio"
+    "pigpio",
+    "raspberry",
+    "pi"
   ],
   "author": "depuits",
   "license": "ISC",
   "bugs": {
     "url": "https://github.com/depuits/pigpio-dht/issues"
   },
   "homepage": "https://github.com/depuits/pigpio-dht#readme",
-  "devDependencies": {
-    "pigpio-mock": "0.0.1"
-  },
   "dependencies": {
     "pigpio": "^0.6.4"
   }