μReflow Oven with MicroPython & LittlevGL

中文版请见于此。

WARNING: when updating from a previous version, make sure to get the latest config.json and carefully verify that it reflects your system configuration. First and foremost make sure that the heater is configured to the right polarity.

Updated! Now the μReflow Oven is PID control enabled!

For previous version which is non-PID controlled, pls see the branch Adafruit-EZ-Make-Oven-alike.

This project is an improved and heavily modified version of Adafruit EZ Make Oven. The original code of EZ Make Oven can be found here.

The purpose is to make a reflow soldering oven by modifying a kitchen oven with more affordable and widely available hardwares. Instead of an oven, a heating plate can also be used.

The GUI of this project is built with LittlevGL (lv_binding_micropython) which is a very powerful and easy to use GUI library. LittlevGL already comes with drivers for ILI9341 TFT display and XPT2046 touch controller, this project takes the advantage of both to ease the user operation.

Bill of Materials

• 1 x regular kitchen oven with 10-12L capacity, like this, OR a heater plate, like this.
• 1 x solid state relay rated at least 10A. Like this (the heater plate linked above already includes it).
• 1 x passive piezo buzzer. Like this.
• 1 x ILI9341 TFT display with on-board XPT2046 touch controller. Like this.
• 1 x Thermocouple amplifier with K-thermocouple. So far, MAX31855 and MAX6675 are supported. MAX31855 MAX6675
• 1 x AC-DC5v power supply to power the ESP32 dev board. Like this.
• 1 x ESP32 dev board. Like this.

Oven Modification and Wiring

• WARNING: The mains (220/110V) can be deadly. Make sure the oven is unplugged from the outlet before doing any modification or wiring.
• Ovens are different one from another, but basically all you need to do is to bypass the original switch and timer, and let the solid state relay control the heating element, hence the ESP32 board can turn the heating element on and off via the solid state relay.

The Firmware for ESP32

• Pls refer to here.

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Configuration

• Configuration is done by editing the config.json file.
• Hardware wiring: edit the value of the key names ending with '_pins' to match your actual wiring.
• The TFT screen and the touch controller share the same Clock, Data In & Data Out pins.
• The ACC pin is for switching power of the TFT screen. This pin is optional. If your display has an input to switch power (often labeled ACC), you may connect the designated GPIO directly to this pin. Alternatively, you could use a transistor to switch the power supply of the screen. It has been reported that the screen can even be powered directly from a GPIO pin, however note that an ESP32 GPIO pin can drive at most 50mA (according to specification) and a typical 2.8" screen will draw between 80mA and 250mA, so this method risks damaging your ESP32. Since this pin is optional, you may safely ignore it (simply wire the 3V3 pin of the screen to the 3V3 output of the ESP32).
• The active_low properties can be used to make a pin active low.
• sampling_hz determines the update rate of the temp sensor and the PID controller. The default setting 5 means 5HZ which is 5 times per second.
• temp_offset & pid parameters can be set in the settings of the GUI.
• advanced_temp_tuning can only be changed by editing the config.json.
  • preheat_until (temperature in Celsius) is used to set a temperature below which the oven will always be on - it helps to heat up the oven as quickly as possible at the early stage.
  • previsioning (time in Second) is for the PID to look for the set temp X seconds ahead, as the reflow temperature profile is not constant but a changing curve, this parameter will make the PID more reactive.
  • overshoot_comp (temperature in Celsius) it helps reduce the overshoot.

FTP access

• The above mentioned advanced_temp_tuning may need some trial and error. To make the fine tuning process a bit easier, the ESP32 will create a WiFi access point named Reflower ftp://192.168.4.1
• Simply connect to that SSID and you can edit the config.json by logging in 192.168.4.1:21 via an FTP client, e.g. FileZiila.

Installation

• All files are under MAIN folder.
• After flashing the firmware, you need to edit config.json to change the GPIO pin numbers according to how you wiring your TFT display and other components.
• Set sensor_type to either MAX31855 or MAX6675.
• Some solid state relays will not switch on with the little current supplied by an ESP32 GPIO pin. In this case you have to use a transistor between the GPIO pin and the SSR. You may need to configure the pin as active low then.
• Make sure you have configured the right polarity for all pins.
• Transfer all the files and folder under MAIN to the ESP32 dev board and you are good to go.

Usage Guide

• Upon powering on the first time, you will be guided through touch screen calibration, once finished, the ESP32 will reboot.
• After calibration and reboot, the GUI will load, where you can select Solder Paste type from the drop-down menu, just choose the type you'll use, and the reflow temperature profile will show down below.
• If your solder paste isn't there in the menu, you can build your own solder profile files. Pls refer to: https://learn.adafruit.com/ez-make-oven?view=all#the-toaster-oven, under chapter "Solder Paste Profiles". The new solder profile json file should be put under folder profiles.
• All set and click "Start" button to start the reflow soldering procress.
• If you wish to re-calibrate the touch screen, click the 'Settings' button on the screen, and choose from the popup window. And follow the on-screen instruction.

PID tuning tips

• Firstly, set previsioning & overshoot_comp to 0 in config.json to avoid confusing behavior.
• Set kp to a small value, e.g. 0.1, and kd to a large value, e.g. 300. This helps to minimize overshooting during the early stage which is typically seen in 'preheat' and 'soak' stage. Keep decreasing/increasing kp/kd value until minimum overshooting is observed.
• With a small kp & a large kd, it's very hard for the actual temp to reach the peak temp of the ideal reflow profile, this is when you need to tune the value of ki. Slowly increase ki until the actual peak temp gets really close to the ideal profile.
• Pls note that the integration part (where ki takes effects) of the PID algorithm is only enabled when it reaches 'reflow' stage - this is hard coded and cannot be changed by settings. The intention is to prevent overshooting in the early stage while it still can reach the peak temp of the ideal profile.