Temperature Sensor

Setup

The following two commands load the 1-Wire and thermometer drivers on GPIO 4.

sudo modprobe w1-gpio
sudo modprobe w1-therm

We then need to change directory cd to our 1-Wire device folder and list ls the devices in order to ensure that our thermometer has loaded correctly.

cd /sys/bus/w1/devices/
ls

In the device drivers, your sensor should be listed as a series of numbers and letters. In this case, the device is registered as 28-000005e2fdc3. You then need to access the sensor with the cd command, replacing our serial number with your own.

cd 28-000005e2fdc3

The sensor periodically writes to the w1_slave file, so we simply use the cat command to read it.

cat w1_slave

This yields the following two lines of text, with the output t= showing the temperature in degrees Celsius. A decimal point should be placed after the first two digits e.g. the temperature reading we’ve received is 23.125 degrees Celsius.

72 01 4b 46 7f ff 0e 10 57 : crc=57 YES

72 01 4b 46 7f ff 0e 10 57 t=23125

The Node Package ds18x20 is used to provide a Javascript API to these devices.https://www.npmjs.com/package/ds18x20

This is a service which emits the temperature for all connected temperature sensors. It is built upon the npm dsx1820 package.

var temp_svc = require('temp_svc.js');

Before emitting data, the service requires to be started.  Once started it emits temperature events every 10 seconds..

emitter = temp_svc.start();
temp_svc.stop();

Periodically the temperature from all sensors are emitted to all listeners.

emitter.listen("temp", function(name,value){
  console.log(name, value);
});
{ ‘Kettle Inlet: 22.9, ‘Mash Tun outlet: 22.8 }

The temperature is requested from each sensor. The result is returned in Celsius degrees and rounded to one decimal place.

temp_svc.currentTemp(function(result){
  console.log(result);
});

Temperature in ° C

{ 28-00000574c791: 22.9, 28-00000574f4f3: 22.8 }

TBD

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