Nov 062016

During today’s Dev Japan Meetup I finally had the time to do something I always wanted to do but never had time to implement: Create a fast link from an end-device (AKA browser or phone application) to my LED display. That display is a simple 10×10 WS2812 LEDs strip originally connected to an Arduino with a Bluetooth receiver, but replaced by a Wemos D1 mini flashed with Espruino since that has WiFi and more RAM.

Here the important (but incomplete) part of the Espruino program:

var host = "";
var WebSocket = require("ws");
var ws = new WebSocket(host,{
  path: '/',
  port: 8080, // default is 80
  protocol : "echo-protocol", // websocket protocol name (default is none)
  protocolVersion: 13, // websocket protocol version, default is 13
  origin: 'Espruino',
  keepAlive: 60

ws.on('open', function() {
  console.log("Connected to server");

ws.on('message', function(msg) {
  console.log("MSG: " + msg);
  if (msg == "R") {
    colorize(40, 10, 10);
  } else if (msg == "G") {
    colorize(10, 40, 10);
  } else if (msg == "B") {
    colorize(10, 10, 40);
  esp8266.neopixelWrite(NodeMCU.D4, leds);

The logic is as simple as it looks: connect to a WS server and wait for incoming messages. If it’s “R”, or “G”, or “B”, then colorize the LED array.

Here a section of the browser part:

var ws = new WebSocket("ws://");

ws.onopen = function(evt) {
  var conn_status = document.getElementById('conn_text');

ws.onmessage = function(evt) {
  var newMessage = document.createElement('p');
  newMessage.textContent = "Server: " +;

ws.onclose = function(evt) {
  alert ("Connection closed");

$(".color").click(function(evt) {

and the buttons look like

<button type="submit" class="color" val="R">Red</button>
<button type="submit" class="color" val="G">Green</button>
<button type="submit" class="color" val="B">Blue</button>

The one missing part is the websocket server in the middle which relays messages, which I took quite literally from here from the Espruino Websocket docs.

This is anything but clean code, and not yet a complete and instructive example application, but it’s the first step and a good proof-of-concept.

Next step is a web page to have a 10×10 grid of buttons which can be turned on/off by touching, and the corresponding commands are sent to the LED display.

Oct 302016

Lua is neat, but learning Lua and JavaScript and NodeJS. Although Lua and especially NodeMCU is similar (not only in name) to NodeJS, it would be nicer to use only one language.

Here the recipe:

  1. Download espruino_1v87.tve_master_b3dc05b_esp8266.tgz
  2. Write flash (note: might use 80m and qio, but my old one does dio):
    ./ --port /dev/ttyUSB0 --baud 115200 write_flash --flash_freq 40m --flash_mode dio --flash_size 32m \
    0x0000 ~/Downloads/espruino_1v87.tve_master_b3dc05b_esp8266/boot_v1.6.bin \
    0x1000 ~/Downloads/espruino_1v87.tve_master_b3dc05b_esp8266/espruino_esp8266_user1.bin \
    0x3FC000 ~/Downloads/espruino_1v87.tve_master_b3dc05b_esp8266/esp_init_data_default.bin \
    0x37E000 ~/Downloads/espruino_1v87.tve_master_b3dc05b_esp8266/blank.bin
  3. Verify it:
    ./ --port /dev/ttyUSB0 --baud 115200 verify_flash \
    0x1000 ~/Downloads/espruino_1v87.tve_master_b3dc05b_esp8266/espruino_esp8266_user1.bin \
    0x3FC000 ~/Downloads/espruino_1v87.tve_master_b3dc05b_esp8266/esp_init_data_default.bin \
    0x37E000 ~/Downloads/espruino_1v87.tve_master_b3dc05b_esp8266/blank.bin
  4. Connect at 115200bps.
  5. Connect to your AP:
    var wifi = require("Wifi");
    wifi.connect("your_sid", {password:"your_password"}, function(err){
     console.log("connected? err=", err, "info=", wifi.getIP());
  6. In the Espruino IDE add the IP address
  7. When you reconnect via Espruino IDE, you should now have 2 choices: serial or TCP/IP via WLAN


Oct 162016
Node-RED: Functions

My light sensor (actually just a LDR connected to the single ADC pin on the ESP8266) tends to be a bit jumpy and the graphs looked anything but smooth. Quick fix: averaging samples. Node-RED has functions for this. And here is one to average 4 samples:

// jshint esversion: 6

const oldDataMax=4;
let lastData;
let count = context.get('count')||0;
let oldData = context.get('oldData')||[];

// Need to shift all numbers one left if array full
// Circular buffer would be nice, but overly complex for such small buffers

if (count==oldDataMax) {
 for (let i=1; i<oldDataMax; ++i) {
} else {

// Calculate the average

let avg=0;
for (let i=0; i<=lastData; ++i) {

context.set('count', count);
context.set('oldData', oldData);

let avgMsg = { payload: ""+avg };

return [ msg, avgMsg ];

Much less jumpy graphs now!


Aug 142016

When you have a microcontroller which can connect to the network and it has a RGB LED, the logical step is to make this LED controllable via a web browser.

The list of issues faced is numerous:

  • NodeMCU does not handle websockets natively
  • Thus a bridge between normal TCP sockets used by NodeMCU and WebSockets used by the web browser is needed: ws-tcp-bridge does that
  • ws-tcp-bridge defaults to binary blobs which the browser cannot handle. Switching the websocket’s binaryType to arraybuffer fixes this
  • Sending data too fast to a just created websocket which has its binaryType not yet changed to arraybuffer breaks ws-tcp-bridge with a fatal error:
    TypeError: “list” argument must be an Array of Buffers
  • NodeMCU uses Lua, the browser JavaScript. The langages are quite similar! See below for an example.

Code is at

Interesting is the comparison of Lua and JavaScript variable names are the same):

JavaScript Lua
for (c of s.split('')) {

  if (c>='0' && c<='9') {
    if (state==1)

    } else {
      if (state==1) {
        setOneColor(color, value);
      if (c=='R' || c=='G' || c=='B') {
for n=1,s:len(),1 do
   c=s:sub(n, n)
   if c>='0' and c<='9' then
     if state==1 then
     if state==1 then
       setOneColor(color, value)
     if c=='R' or c=='G' or c=='B' then