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Firmware for a DIY Reflow Hot-Plate like "Tim's Hot Plate"

One of my "Tim's Hot-Plate" builds

A feature-rich reflow Hot-Plate firmware, i.e. usable for "Tim's Hot Plate"

Introduction

I was in the need for a reflow soldering Hot-Plate.

After evaluating a couple of good projects, I decided to build "Tim's Hot Plate" as it had a very detailed and quite good description, as well as I like the way how he did it with less or minimal external parts.

It was quickly build up and it worked quite good so that I could do my reflow soldering project for which I needed the Hot-Plate.

But: I decided for a larger (and more powerfull) 400W PTC as well as I mounted the Thermocouple in a different way as Tim did/described in his description. The result was, that I had to struggle with quite large overshooting (up to +40°C). Not a big deal as it was fairly easiable to compensate this overshooting by choosing a smaller target temp before reaching the real target temp.

However, during the reflow of a coulpe of prototype PCB's, the overshooting workaround started to annoy me, as well as I got a couple of ideas (while rotating the knob and watching/waiting for the target temperature).

As we all have some kind of fetish, and mine seem to be that I tend to over-optimize things others are fine with, I decided trying to build a more feature-rich firmware alternative.

Features

Setup

Built-in "Setup" within Hot-Plate user interface

Built-in Setup

Reflow Profile

"Manual" or (open-end) "Reflow-Profile" Mode, with built-in reflow profiles for low-temp. solder paste Sn42/Bi57.6/Ag0.4, as well as high-temp. Sn96.5/Ag3.0/Cu0. After (as well as during) the reflow profile time targets, the user may adapt the target temp. (every 10 seconds). At profile end, the last target temp remain active and the user has to stop the profile manually when everything reflowed correctly.

Reflow Profiles Reflow Profile Start Running Reflow Profile

PID Tuner support

Simply start an automatic step response run, with a connected serial console. Afterwards copy the resulting data into PID Tuner and (auto-)tune your PID constants. BTW: This step response can also be used to determine the overshot of the tuned target temperatures which might be used (at least as indication) for the BangON setting.

Setup BangON Setup BangOFF Setup BangOFF Setup BangOFF

PID constants

Either you know your PID constants, evaluate them the hard way "by hand" or use PID Tuner support for assistance in PID constant determination.

Setup PID constant Kp Setup PID constant Kd Setup PID constant Ki

BangON/BangOff

Quick start/Overshoot reduction settings and functionality. Mainly for bad/non-configuraed PID controller constants. A good configured PID controller normally does not need BangON/BangOFF, but PID controller constant determination is complicated and time consuming. See PID Tuner support for assistance in PID constant determination.

Setup BangON Setup BangOFF

SSR type

Active-low/high configurable within buit-in setup

Setup SSR Type

Save

Save of settings to EEPROM possible within built-in setup

Setup Save

Requirements

Assembled DIY Hot Plate like described in "Tim's Hot Plate" which is based on the following components

  • ATmega328 like Arduino Nano 3.x
  • Some kind of cheap AC-Mains powered PTC heater (200-400W)
  • SSR (active- high or low) which has enough power to switch your selected PTC
  • Convenient K-Type Thermocouple
  • MAX6675 Module
  • SSD1306 0.96" I2C OLED 128x64 Display
  • Rotary EC11 Encoder

Roadmap

  • Step response output for easier PID constant determination by the help of PID Tuner
  • Some kind of PID loop tuning/calibration
  • Ramp-up determination to identify PTC time and TC delay (BangON calibration)
  • Progressive rotary switching for quicker +/- move
  • C/F unit selection (if someone is interested in)
  • Larger display so that I don't need my glasses (old man wish)

Known Bugs/Issues

  • I've the impression that the Ki constant of the (currently) used AutoPID doesn't behave as expected -> Now fixed

Technology

The code structure is PlatformIO/VSCode based (no Ardino-IDE test or support).

Installing

  1. Upload .hex or .elf file WITHOUT HAVING AC-MAINS CONNECTED
  2. Long-press (> 0.5s) to get into built-in setup
  3. Choose "SSR Type"
  4. Select your SSR type (Active-Low/High). In the case of Tim's Hot Plate it will be "Active-Low"
  5. Choose "Save & Quit"
  6. Plug-in AC-Mains. Happy reflow soldering...

Usage

  • Rotate knob for +/- or up/down
  • Push knob to stop (or start profile if it's displayed on screen)
  • Long-Push (> 0.5s) to get into built-in setup

Built With

  • Tim's Hot Plate - Quite cool DIY reflow Hot Plate Project @ Instructables
  • U8g2 - Excellent and powerful Library for monochrome displays, version 2
  • MAX6675 - Arduino library for interfacing with MAX6675 thermocouple amplifier
  • CRC32 - An Arduino library for calculating a CRC32 checksum
  • AutoPID - Fairly good documented (as well as feature rich and small) Arduino AutoPID library
  • PID Tuner - Will help you to finde reasonable PID constants

Contributing

Please read CONTRIBUTING.md for details on our code of conduct, and the process for submitting pull requests to us.

Versioning

We use SemVer for versioning.

For the versions available, please see changelog file or the tags on this repository.

Authors

License

This project is licensed under the GNU General Public License 3 (GPL-3.0) - see the LICENSE.md file for details