Having seen a tweet to a Hackaday article (/ht Andy Piper) about adding a ESP8266 to the new IKEA VINDRIKTNING air quality sensor.

IKEA Air Quality Sensor showing Green Light

The sensor is a little stand alone platform that measures the amount of PM 2.5 particles in the air and it has an array of coloured LEDs on the front to show a spectrum from green when the count is low and red when high.

Sören Beye opened one up and worked out that the micro controller that reads the sensor to control the leds does so over a uart serial connection and that the Tx/Rx lines were exposed via a a set of test pads along with 5v and Ground power. This makes it easy to attach a second micro controller to the Rx line to read the response when the sensor is polled.

Sören has written some code for an ESP8266 to decode that response and publish the result via MQTT.

Making the hardware modification is pretty simple

Wemos D1 Mini attached to sensor
  • Unscrew the case
  • Strip the ends on 3 short pieces of wire
  • Solder the 3 leads to the test pads labelled 5v, G and REST
  • Solder the 5V to 5V, G to G and REST to D2 (assuming using a Wemos D1 Mini)
  • Place the Wemos in the empty space above the sensor
  • Screw the case back together

The software is built using the Ardunio IDE and is easily flashed via the USB port. Once installed when the ESP8266 boots it will set up a WiFi Access Point to allow you to enter details for the local WiFi network and the address, username and password for a MQTT broker.

When connected the sensor publishes a couple of messages to allow auto configuration for people who use Home Assistant but it also publishes messages like this:

    "ssid":"IoT Network",

It includes the pm25 value and information about which network it’s connected to and it’s current IP address. I’m subscribing to this with Node-RED and using it to convert the numerical value, which has units of μg/m3 into a recognised scale (found on page 4).

let pm25 = msg.payload.pm25
if ( pm25 < 12 ) {
  msg.payload.string = "good"
} else if (pm25 >= 12 && pm25 < 36) {
  msg.payload.string = "moderate"
} else if (pm25 >= 36 && pm25 < 56) {
  msg.payload.string = "unhealthy for sensitive groups"
} else if (pm25 >= 56 && pm25 < 151 ) {
  msg.payload.string = "unhealthy"
} else if (pm25 >= 151 && pm25 < 251 ) {
  msg.payload.string = "very unhealthy"
} else if (pm25 >= 251 ) {
  msg.payload.string = "hazardous"
return msg;

I’m feeding this into a Google Smart Home Assistant Sensor device that has the SensorState trait, this takes the scale values as input, but you can also include the raw values as well.

msg.payload = {
        "rawValue": msg.payload.pm25
return msg;

I will add the an Air Quality trait to the Node-RED Google Assistant Bridge shortly.

I’m also routing it to gauge in a Node-RED Dashboard setup.

Quick and Dirty Finger Daemon

I’ve been listening to more Brad & Will Made a Tech Pod and the current episode triggered a bunch of nostalgia about using finger to work out what my fellow CS students at university were up to. I won’t go into to too much detail about what Finger is as the podcast covers it all.

This podcast has triggered things like this in the past, like when I decided to make this blog (and Brad & Will’s podcast) available via Gopher.

On the podcast they had Ben Brown as a guest who had written his own Finger Daemon and linked it up to a site called Happy Net Box where users can update their plan file. Then anybody can access it using the finger command e.g. finger hardillb@happynetbox.com . The finger command is shipped by default on Windows, OSx and Linux so can be accessed from nearly anywhere.

I really liked the idea of resurrecting finger and as well as having a play with Happy Net Box I decided to see if I could run my own.

I started to look at what it would take to run a finger daemon on one of my Raspberry Pis, but while there are 2 packaged they don’t appear to run on current releases as they rely on init.d rather than Systemd.

Next up I thought I’d have a look at the protocol, which is documented in RFC1288. It is incredibly basic, you just listen on port 79 and read the username terminated with a new line & carriage return. This seamed to be simple enough to implement so I thought I’d give it a try in Go (and I needed something to do while all tonight’s TV was taken up with 22 men chasing a fall round a field).

The code is on Github here.

package main

import (

const (
  CONN_HOST = ""
  CONN_PORT = "79"
  CONN_TYPE = "tcp"

func main () {
  l, err := net.Listen(CONN_TYPE, CONN_HOST+":"+CONN_PORT)
  if err != nil {
    fmt.Println("Error opening port: ", err.Error())

  defer l.Close()
  for {
    conn, err := l.Accept()
    if err != nil {
      fmt.Println("Error accepting connection: ", err.Error())
    go handleRequest(conn)

func handleRequest(conn net.Conn) {
  defer conn.Close()
  currentTime := time.Now()
  buf := make([]byte, 1024)
  reqLen, err := conn.Read(buf)
  if err != nil {
    fmt.Println("Error reading from: ", err.Error())
  } else {
    fmt.Println("Connection from: ", conn.RemoteAddr())

  request := strings.TrimSpace(string(buf[:reqLen]))

  parts := strings.Split(request, " ")
  wide := false
  user := parts[0]

  if parts[0] == "/W" && len(parts) == 2 {
    wide = true
    user = parts[1]
  } else if parts[0] == "/W" && len(parts) == 1 {

  if strings.Index(user, "@") != -1 {
    conn.Write([]byte("Forwarding not supported\r\n"))
  } else {
    if wide {
    } else {
      pwd, err := os.Getwd()
      filePath := path.Join(pwd, "plans", path.Base(user + ".plan"))
      filePath = path.Clean(filePath)
      file, err := os.Open(filePath)
      if err != nil {
        //not found
        // io.Write([]byte("Not Found\r\n"))
      } else {
        defer file.Close()

Rather than deal with the nasty security problems with pulling .plan files out of peoples home directories it uses a directory called plans and loads files that match the pattern <username>.plan

I’ve also built it in a Docker container and mounted a local directory to allow me to edit and add new plan files.

You can test it with finger ben@hardill.me.uk