Water metering

Works in progress! I'm not done with migrating this setup to Homey yet!
This article describes the setup of digitally measuring water usage, using a tessel.io microcontroller.
Choosing the correct water meter
You are not allowed to install a water meter yourself. In dialog with the waterworks, ro replace or install a water meter you need to ask for a water meter that can support digital readings.
In Trondheim, Norway, Øwre-Johnsen as delivers the water meters allowed to be installed.
In dialoge with Øwre-Johnsen as, I ended up installing Elster V200 (KVM-T). In addition I ordered and installed the Falcon PR6 pulse module. This one you can install your self.
Reading the pulse
I chose to use a tessel.io microcontroller, because it has both analog and digital gpio ports that is very easy to interact with using javascript.
The Falcon PR6 contains a battery and gives a digital impulse every liter user detected. Connect the black wire to GND and the yellow to one of the numbered PINs.
And when/if you order a Tessel 2, remember to also order a set of jumper wiresthat fits.
Here is a class to read the pulse indicating one liter used.
const  
  EventEmitter = require('events'),
  tessel = require('tessel')
​
const pin = tessel.port.A.pin[4]
​
class PulseReader extends EventEmitter {  
  constructor() {
    super()
    this.previous = false
    setInterval(() => {
      this.read()
    }, 50) // Read impulse every 50 ms
  }
​
  // Give a short blue LED blink to signal that an pulse is detected.
  blink() {
    blue.on()
    setTimeout(function () {
      blue.off()
    }, 100);
  }
​
  read() {
    pin.read((error, value) => {
      if (error) {
        console.error("Error reading analog input: " + error)
        return
      }
      let val = (value === 0)
​
      // Emit a value event every time a digital pulse is detected
      // Will discard all subsequent readins from the same pulse
      if (val && val !== this.previous) {
        this.emit('value', true)
        this.blink()
      }
      this.previous = val
    })
  }
}
​
module.exports = PulseReader
It can be used like this:
let d = new Database()  
let p = new PulseReader()
​
p.on('value', (value) => {  
  d.post(1)
})
​

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Outline

Choosing the correct water meter

Reading the pulse