Making my own reflow hot plate from scratch - Part 1 - Prototype

Apr 14

This is the first video of another video series on a project that I am working on. The subject this time is a fully customized reflow hot plate from scratch. I put together a relatively system using a few components as a first iteration. The system consists of an Arduino Nano as the main microcontroller, a MAX6675 K-type thermocouple module for measuring the temperature of the hot plate, a TRIAC switch circuit to switch the heating plate on and off and a 1.8” 128x160 TFT LCD to visualize everything. The controlling of the heating plate is very simple: I created a formula that based on the user-created reflow curve determines the temperature at a given moment and the code checks if we are above or below this temperature. The heater is turned on if we are below the target (or setpoint), and it turns off if we are above it. This is a very simple ON/OFF switching that has its drawbacks and advantages, but I can accept its drawbacks for the first iteration of this circuit.

Regarding the user interface, I went above and beyond and I tried to create a very flexible way of entering any kind of custom reflow curve. I also made it possible that during heating, a real-time time vs. temperature curve is being plotted over the user-defined reflow curve as well as information such as the target temperature, elapsed time, actual program…etc. is also shown.

Schematics and some photos

You can buy the relevant parts using the following affiliate links:

Arduino Nano

MAX6675 thermocouple module

1.8” TFT LCD

TRIAC switch module

Rotary encoder module

Blower fan

300 W Heating plate

A custom reflow curve

This is the main screen. Each temperature (red) and time (white) values can be modified using a rotary encoder. The user can create any custom reflow curve within reasonable limitations. The start button starts the heating program.

A finished heating program

Here is a finished program, currently in the cooling phase. The user-defined reflow curve is in the background and the cyan colored curve is the time-temperature diagram measured real-time during the heating program.

Result of the very first soldering

Actually, I haven’t tested the heater if I can solder with it. The very first soldering was done while I made the video. This is the result. Of course, I messed up the solder paste application, but still it is an acceptable result.

Imperfections

Here you can see some imperfections due to the excess solder paste.

Imperfections

Here you can see some imperfections due to the excess solder paste.

Arduino Nano

These are the connections of the Arduino Nano. The Nano, based on the power brick used takes the power either at its VIN pin or +5V pin. The MCU takes care of a rotary encoder, an LCD display, and a MAX6675 module.

TRIAC switch

This is a general optocoupler-TRIAC circuit. I also added a power brick to the circuit which will provide the power for the Arduino and its peripherals. An additional connection for the protective earth (not the same as GND) is also added.

Transistor switch for the fans

A simple BD139-based switch for the two fans. The obligatory diode is added to the motors. Pick the fans according to the output power of your power supply!