Pomodoro on ESP-32

Implementation of the Pomodoro technique on the ESP-32 microcontroller.

Each transition between work and rest cycle is indicated by one or multiple physical stimulus (melody and/or color).

A display indicates the progression of the timer and double as an NTP clock.

Table of content

• Pomodoro
• Electronic circuit
  • Schematic
  • Materials
    • Note on the seven-segments display and shift-register
• Software
  • Design
  • Dependency
• Tool
  • Seven-segment display value

Pomodoro

Pomodoro is a time management technique that use a timer to break down task and rest period.

Electronic circuit

Schematic

Materials

Type	Designation	Quantity
System on a chip	ESP-WROOM-32	1
4 digit 7 segment display	HS420561K-32	1
8-bit shift register	SN74HC595N	1
Transistor	PN2222	4
Diode		3
Passive buzzer		1
Momentary Switch		1
Resistor	220 Ω	11
Resistor	4.7 kΩ	4

Note on the seven-display segment and shift-register

You might have notice that it's not the prettiest way to use a 4-digits seven-segments display.

Initially I wanted to use one shift-register per digit, but as I found only one SN74HC595N on my parts bins, I ultimately decided to make do. The result is a bit messier but works.

Software

Design

This software make use of the two core of the ESP-32, and it's FreeRTOS implementation to have two tasks:

1. Display the time remaining on the clock and use interrupt to count each second passed.
2. Alarm the user of a transition between task and rest with the use of melody and visual cue.

Dependency

Ignoring the common library use in almost every project (like stdint.h, Arduino.h, esp32-hal-ledc.h or HardwareSerial.h), the code make use of:

• pitches.h from arduino to create melody using the piezo speaker. Included in lib/pitches.h for ease of deployment.

Tool

Seven-segment display value

To ease the transition between physical segment and binary/hexadecimal code, I created a small HTML tool tool/SevenSegmentDisplayValue.html.