TPMS - Tire Pressure Monitoring System

Followup from this thread and now pimped up to be of actual use on the infamous Pixl.js.

Hardware

1. cheap BLE 4 enabled set of 4 thimble-sized tire pressure sensors (search for TPMS - V11 on eBay or Aliexpress):
   
   
2. Pixl.js module
   
   

Software

// define your tires here (2-4)
const tires = {
  '207bdd': {
    name: 'FL',
    minBar: 7.0,
    minBat: 20,
  },
  '30bc95': {
    name: 'FR',
    minBar: 7.0,
    minBat: 20,
  },
  '10ba52': {
    name: 'R',
    minBar: 5.5,
    minBat: 20
  }
};

const ALARM_BAR = 0x01;
const ALARM_BAT = 0x02;
const ALARM_LEAK = 0x04;
const ALARM_TIME = 0x08;

var dirty = 1;
const timeout = 120;

var flashTimer;

function setFlash(on) {
  if(on) {
    if(flashTimer == undefined) {
      flashTimer = setInterval(function(){
        digitalPulse(LED1, 1, [100]);
      }, 1000);
    }
  }
  else {
    if(flashTimer) {
      clearInterval(flashTimer);
      flashTimer = undefined;
    }
    LED1.reset();
  }
}


function analyze() {
  var flash = 0;
  for(let id in tires) {
    var alarm = 0;
    var d = tires[id];
    if(d.t > 0) {
      // underpressure
      if(d.bar < d.minBar) {
        alarm |= ALARM_BAR;
      }
      // battery low
      if(d.bat < d.minBat) {
        alarm |= ALARM_BAT;
      }
      // signal loss
      if(d.t + timeout < getTime()) {
        alarm |= ALARM_TIME;
      }
      // leak
      if(d.leak) {
        alarm |= ALARM_LEAK;
      }
    }
    else {
      tires[id].t = getTime();
    }
    if(alarm > 0) {
      flash = 1;
    }
    tires[id].alarm = alarm;
  }
  setFlash(flash);
}

function out(text, x, y, inverse) {
  if(inverse) {
    g.fillRect(x, y, x + g.stringWidth(text) + 2, y + g.getFontHeight() - 1);
    g.setColor(0, 0, 0);
  }
  g.drawString(text, x + 1, y);
  g.setColor(1, 1, 1);
}

function draw() {
  g.clear();
  var y = 0;
  out('TPMS', 0, 0, 1);
  for(let id in tires) {
    y += g.getFontHeight();
    var d = tires[id];
    g.drawString(d.name, 0, y);
    if(d.bar != undefined) {
      out(d.bar.toFixed(1), 25, y, d.alarm & ALARM_BAR);
      out(d.temp.toFixed(1) + '°C', 55, y);
      out(d.bat + '%', 95, y, d.alarm & ALARM_BAT);
    }
    else {
      out('...', 50, y);
    }
    if(d.alarm & ALARM_TIME) {
      out('?', 120, y, 1);
    }
    else if(d.alarm & ALARM_LEAK) {
      out('!', 120, y, 1);
    }
  }
  g.flip();
}

function decodeData(device) {
  var d = new DataView(device.manufacturerData);
  var id = d.getUint32(2).toString(16).slice(-6);

  if( tires[id] != undefined ) {
    tires[id].t = getTime();
    tires[id].bar = d.getUint32(6, 1) / 100000;
    tires[id].temp = d.getUint32(10, 1) / 100;
    tires[id].bat = d.getUint8(14);
    tires[id].leak = d.getUint8(15);
    dirty = 1;
  }
}


function onInit() {
  require("FontDylex7x13").add(Graphics);
  g.setFontDylex7x13();
  analyze();
  draw();

  NRF.setScan(function(device){
    decodeData(device);
  }, {
    filters:[{
      services: ['fbb0']
    }]
  });

  setInterval(function(){
    if(dirty) {
      analyze();
      draw();
      dirty = 0;
    }
  }, 5000);
}

onInit();

Function

The sensors do not require a connection or traversing Services and Characteristics.
All the data is just put into 16 bytes of manufacturerData found in each broadcast:

• Bytes 0-5: pevice ID
  
• Bytes 6-9: pressure (Pascal, Bar * 100000)
  
• Bytes 10-13: temperature (°C * 100)
  
• Byte 14: Battery (%)
  
• Byte 15: Flat (flag - 0=OK, 1=detected)
  
  

The sensor seems to:

• Sleep when no pressure detected (no transmissions at all)
  
• Transmit as soon as a change appears (with a few seconds delay)
  
• Transmit at least every 60 seconds when pressure detected
  
  

The set contains a card showing the last 6 hex digits of each device.
You can copy these digits (lower case) to the object on top of the code.
Everything from 1-4 wheels is possible. I only use 3 wheels because I own a Velomobile, but everything from unicycle to car is possible.

For each wheel you can define an individual name, a minimum pressure minBar and a minimum battery percentage minBat.

Underpressure, low battery, loss of signal (stale data for more than timeout seconds) and leaks are detected.
There is a flag (I called it leak that seems to show 1 when the pressure is starting to decrease at a certain rate and/or the temperature is rising but the pressure is not).

When any issue is detected, LED1 begins to flash and the value gets inverted.
This is how it looks:

1 Attachment