Pixl.js Simple Logger

This example shows you how to build a simple device to let you count things happening each day, graph (and export) the result. Scroll down to see how to attach external sensors or use Puck.js to modify the counter remotely.

Maybe you're growing Tomatoes and you want to count how many you get off your plant each day, or maybe you're counting the amount of times your coworker does something annoying.

To use this, just get a Pixl.js, connect with the Espruino IDE, copy the code below into the right-hand side of it, and click 'Upload'.

When it's running, you just use the right-hand upper and lower buttons to increment or decrement the counter. Each day within an hour of midnight, the counter is zeroed and another bar is added to the graph.

To export your data, connect again with the Web IDE and type toCSV() in the left-hand pane. A comma-separated list of dates and numbers will be printed which you can then copy and paste into Excel or the spreadsheet of your choice.

Data Storage

This code only keeps the data in RAM, so it will be lost if power is removed. You could easily use the Storage Module to store the data when it changes, however since the current time will be lost, this could be of limited use.

Other Boards

It's pretty straightforward to run this code on non-Pixl.js boards. Just ensure that a variable called g contains an instance of a Graphics class set up for your display, and that BTN2 and BTN3 point to pins attached to two buttons.

var days = [0];
var today = days.length-1;
var currentDay = (new Date()).getDay();

function count(dir) {
  days[today] += dir;
  if (days[today]<0) days[today]=0;

function draw() {
  var mid = 22;
  g.drawString((new Date()).toString().substr(0,10).trim(),mid,50);
  require("graph").drawBar(g, days, {
    x : mid*2, y : 5,
    miny: 0,
    axes : true,
    gridy : 5

setWatch(x=>count(1), BTN2, {repeat:true});
setWatch(x=>count(-1), BTN3, {repeat:true});

function checkDay() {
  var day = (new Date()).getDay();
  if (currentDay != day) {
    today = days.length-1;
    currentDay = day;
setInterval(checkDay, 1000*60*60);

function toCSV() {
  var start = Date.now() - 1000*60*60*24*(days.length-1);
  for (var i=0;i<days.length;i++) {
    var date = new Date(start + i*1000*60*60*24);
    var dateStr = date.toString().substr(0,10).trim();
    console.log(dateStr + "," + days[i]);


Triggering the counter

In the example above, the counter is only triggered by the buttons on the side of Pixl.js. However all you need to do to use an external input is to call count(1) when you want to increase the counter.

Wired Pyroelectric sensor

Just wire a Pyroelectric motion sensor up to Vin and GND on your Pixl.js, and connect the signal wire to any input - the example uses A0.

Then all you need to trigger the counter is to add the line:

setWatch(x=>count(1), A0, {repeat:true, edge:"rising"});

Wireless Puck.js sensor

For wireless connections, you need to run the command Bluetooth.setConsole(true) on the Pixl.js so that you don't get Bluetooth connection information written to the LCD.

Then, get a Puck.js and connect to it with the Web IDE. The following code will connect to the Pixl.js when a button is pressed (remember to change Pixl.js 6155 to your Pixl's name).

function count() {
  NRF.requestDevice({ filters: [{ name: 'Pixl.js 6155' }] }).then(function(device) {
    return require("ble_simple_uart").write(device, "count(1)\n");
  }).then(function() {
  }).catch(function() {
    digitalPulse(LED1, 1, 1000);
    setTimeout(count, 1000);

setWatch(count, BTN, {repeat:true,edge:"rising"});

Note: Espruino can currently only handle a single active connection, at a time, so you can't call count() before the previous call to count() has finished (the Blue LED has gone out). To fix this, just keep track of when Puck.js is busy in a variable.

You can use external inputs in the same way we did for Pixl.js above, or you can (for example) use the following code from this example to use the Magnetometer:

var zero = Puck.mag();
var doorOpen = false;
function onMag(p) {
  p.x -= zero.x;
  p.y -= zero.y;
  p.z -= zero.z;
  var s = Math.sqrt(p.x*p.x + p.y*p.y + p.z*p.z);
  var open = s<1000;
  if (open!=doorOpen) {
    doorOpen = open;
    if (!open) count();
Puck.on('mag', onMag);

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