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Pomodoro With an ESP32: One ''The Melee – Side by Side'' Project

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Pomodoro With an ESP32: One ''The Melee – Side by Side'' Project

Check out the results of this collaborative pomodoro, where a team utilizes an ESP32, Pi Zero, MQTT/mosquitto, and Angular and Node together to create an app.

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Last weekend, there was a great event called The Melee – Side by Side (Many thanks to @ojoven and @diversius).

The event was a kind of Hackathon where a group of people get together one day to share our side projects and to work together (yes, we also have lunch and beer, too!). The format of the event is just a copy of the event that our colleagues from Bilbao called El Comité.

@ibaiimaz spoke about one project to create one collaborative pomodoro where the people of one team can share their status and see the status of the rest of the group. When I heard pomodoro and status, I immediately thought of one servo moving a flag and some LEDs turning on and off. We had a project. @penniath and @tatai also joined us. We also had a team.

We had a project and we also had a deadline. We had to show a working prototype by the end of the day. That means that we didn’t have too much time. First, we decided on the mockup of the project, reducing the initial scope (more ambitious) to fit within our time slot. We discussed intensely for 10 minutes and finally described an ultra-detailed blueprint, seen below:

It was time to start working.

@penniath and @tatai worked on the backend. They were responsible for managing the pomodoro timers, listening to MQTT events, and creating an API for the frontend. The backend also must provide a WebSockets interface to allow for real-time events within the frontend. They decided to use Node and socket.io for the WebSockets. You can see the source code here.

@ibaiimaz started with the frontend. He decided to create an Angular web application listening to socket.io events to show the status of the pomodoro. You can see the source code here.

Finally, I worked with the hardware. I created a prototype with one ESP32, two RGB LEDs, one button, one servo, and a couple of resistors.

Here's the source code.

#include <WiFi.h>
#include <PubSubClient.h>
int redPin_g = 19;
int greenPin_g = 17;
int bluePin_g = 18;
int redPin_i = 21;
int greenPin_i = 2;
int bluePin_i = 4;
#define SERVO_PIN 16
const int buttonPin = 15;
int buttonState = 0;
int channel = 1;
int hz = 50;
int depth = 16;
const char* ssid = "SSID";
const char* password = "password";
const char* server = "";
const char* topic = "/pomodoro/+";
const char* clientName = "com.gonzalo123.esp32";
WiFiClient wifiClient;
PubSubClient client(wifiClient);
void wifiConnect() {
  Serial.print("Connecting to ");
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
  Serial.print("WiFi connected: ");
void mqttReConnect() {
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    if (client.connect(clientName)) {
    } else {
      Serial.print("failed, rc=");
      Serial.println(" try again in 5 seconds");
void callback(char* topic, byte* payload, unsigned int length) {
  Serial.print("Message arrived [");
  String data;
  for (int i = 0; i < length; i++) {
    data += (char)payload[i];
  int value = data.toInt();
  if (strcmp(topic, "/pomodoro/gonzalo") == 0) {
    switch (value) {
      case 1:
        ledcWrite(1, 3400);
        setColor_g(0, 255, 0);
      case 2:
        setColor_g(255, 0, 0);
      case 3:
        ledcWrite(1, 6400);
        setColor_g(0, 0, 255);
  } else {
    switch (value) {
      case 1:
        setColor_i(0, 255, 0);
      case 2:
        setColor_i(255, 0, 0);
      case 3:
        setColor_i(0, 0, 255);  // green
  Serial.print("] value:");
void setup()
  pinMode(buttonPin, INPUT_PULLUP);
  pinMode(redPin_g, OUTPUT);
  pinMode(greenPin_g, OUTPUT);
  pinMode(bluePin_g, OUTPUT);
  pinMode(redPin_i, OUTPUT);
  pinMode(greenPin_i, OUTPUT);
  pinMode(bluePin_i, OUTPUT);
  ledcSetup(channel, hz, depth);
  ledcAttachPin(SERVO_PIN, channel);
  client.setServer(server, 1883);
void mqttEmit(String topic, String value)
  client.publish((char*) topic.c_str(), (char*) value.c_str());
void loop()
  if (!client.connected()) {
  buttonState = digitalRead(buttonPin);
  if (buttonState == HIGH) {
    mqttEmit("/start/gonzalo", (String) "3");
void setColor_i(int red, int green, int blue)
  digitalWrite(redPin_i, red);
  digitalWrite(greenPin_i, green);
  digitalWrite(bluePin_i, blue);
void setColor_g(int red, int green, int blue)
  digitalWrite(redPin_g, red);
  digitalWrite(greenPin_g, green);
  digitalWrite(bluePin_g, blue);

The MQTT server (a mosquitto server) was initially running on my laptop, but I also had one Raspberry Pi Zero in my bag. We decided to use the Pi Zero as a server and run the mosquitto MQTT server with Raspbian. Everything is better with a Raspberry Pi. @tatai helped me to set up the server.

Here you can see the prototype in action:

That’s the kind of side projects that I normally create alone, but it’s definitely more fun to do it with other colleagues, even if I needed to wake up early one Saturday morning.

The ESP32 source code is here.

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