dhtd

Daemon to manage reading DHT temperature sensors on an interval

Summary

This daemon polls the temperature and humidity data on an interval (30 seconds by default), and exposes the information over an HTTP interface.

The DHT sensors for reading temperature data on the Raspberry Pi (Linux) require precise timing that the kernel can't often guarantee. As such, the Adafruit Python DHT Library has baked into it a lot of retry and backoff logic.

To minimize the chance of losing the race with multiple instances of the DHT sensor gathering scripts running simultaneously, this daemon aims to be the single source of truth for the DHT sensor.

Example

Create a simple config

{
  "web": {
    "host": "127.0.0.1",
    "port": 10333
  },
  "dht": {
    "type": 22,
    "pin": 17
  },
  "interval": 30,
  "sudo": true,
  "stats": true
}

• web configures how the HTTP server is setup
• dht tells this program what kind of DHT sensor you are polling (11, 22, or 2302) and what gpio pin it is on
• interval is time in seconds to sleep between readings
• sudo whether to call the python script with sudo, defaults to true
• stats expose stats (hostname, node version, dhtd version) over /stats, defaults to true

And start the program with the config

$ dhtd config.json
2015-08-17T19:08:47.496Z calling: sudo /home/dave/dev/dhtd/_dht.py 22 17
2015-08-17T19:08:57.428Z success: {"fahrenheit": 77.71999931335449, "celsius": 25.399999618530273, "humidity": 45.599998474121094}
2015-08-17T19:08:57.583Z server started: http://127.0.0.1:10333
2015-08-17T19:08:58.924Z 127.0.0.1 GET /data
2015-08-17T19:09:04.294Z 127.0.0.1 GET /data.json

Human readable data is available at GET /data

$ curl -sS localhost:10333/data
fahrenheit: 77.72F
celsius: 25.40C
humidity: 45.60%
reading: 1440088176

And json data at GET /data.json

$ curl -sS localhost:10333/data.json | json
{
  "fahrenheit": 77.71999931335449,
  "celsius": 25.399999618530273,
  "humidity": 45.599998474121094,
  "reading": "2015-08-17T19:08:57.421Z"
}

API

GET /

Returns an index page that shows a thermometer graphic with the current reading that updates every 30 seconds.

GET /ping

Returns 200 and "pong\n"

GET /data

Returns the current data in text format

GET /data.json

Same as above but as JSON

GET /stats

JSON stats if stats is not set to false in the config

Notes

The daemon will wait until an initial reading of the sensor is taking before bringing up the HTTP server. Afterwards, any failures will be recorded in the logs (stdout), but requests to /data and /data.json will have the last previous successful reading data. This is why the reading property exists to see when the last successful reading was.

Installation

Adafruit Python DHT Library

This program depends on the Adafruit Python DHT Library in order to work properly - you can install it with:

sudo apt-get update
sudo apt-get install -y build-essential python-dev
mkdir -p ~/dev
git clone git://github.com/adafruit/Adafruit_Python_DHT ~/dev/Adafruit_Python_DHT
cd ~/dev/Adafruit_Python_DHT
sudo python setup.py install

Node.js

Node version 8 or higher

npm install -g dhtd

Alternatives

• https://github.com/larsks/dhtd - uses a socket file for communication - requires the daemon itself run as root

License

MIT License