Espresso Machine PID controller using ESP32 and RainMaker

Brief description

This project implements a PID/P controller to effectively control the temperature of an Espresso machine boiler, for a stable setpoint. Another feature implemented is the control of the water pump and pre-infusion settings. Combined, these functionalities allow for improved espresso extraction and consistency.

March 2024
https://github.com/raffarost/espresso

Raffael Rostagno
raffael.rostagno@gmail.com

Software

Build and Flash firmware

Follow the ESP RainMaker Documentation Get Started section to build and flash this firmware. Both RainMaker and ESP-IDF environments are necessary.

RainMaker

For the control interface, download RainMaker on your mobile, attach a USB cable to the serial port of the ESP32 board and do the wifi provisioning, after flashing the device with the application firmware.

Hardware

Components used in this project:

• ESP32 DevKitC v4 board
• Dimmer control circuit with Triac and zero-crossing signal
• Thermocouple type K with MAX6675 module
• Simple relay board (3.3V or 5V) with 3A or 5A current rating, 220V or 110V voltage rating
• ULN2003 or similar with free-wheeling diode, to drive relay
• Rapid prototype PCB for water pump drive assembly
• AC to 5V power supply to power Embedded devices
• Jumper wiring

Pinout and wiring

• MAX6675/Thermocouple

  Signal	GPIO
  MISO	19
  MOSI	NC
  CLK	18
  CS	25

• AC Dimmer (Heating element control)

  Signal	GPIO
  ZC (Zero-cross)	5
  DIM (Dimmer)	33

• ULN2003/Relay (water pump control)

  Signal	GPIO
  Relay in	4

Settings

Pinout

Pinout can be chosen according to personal needs and model of SoC used (SPI pins are fixed in some models).

Power grid frequency

For optimal control of the dimmer circuit, please adjust the following define according to your local power grid frequency:

#define GRID_FREQ       60

Type of controller

Three types of controlling algorithm for the heating element are provided:

#define PID         0
#define LOOKUP      1
#define PID_LOOKUP  2

The chosen control mechanism can be selected using the define below:

#define CONTROL_TYPE    LOOKUP

PID calibration

To calibrate the PID controller, the following symbols can be optimized for each application:

#define PID_KP  4.0f
#define PID_KI  2.0f
#define PID_KD  1.0f

#define PID_TAU 0.02f

P calibration (lookup)

To calibrate the P controller, the following vectors can be changed:

static float   deltaBkp[BKP_NUM] = {-10,  0, 0.5,  1,  2,  4, 10,  25,  50, 100};
static float controlSet[BKP_NUM] = {  0,  0,   1,  1,  1,  1,  1,  80, 100, 100};

The first vector corresponds to the temperature difference between target and actual reading. The second vector is the power factor (0 to 100%) to apply for each (interpolated) delta.