Finishing Prototyping

A project log for Reflow Oven

PID Control, Rotary Encoder, Touch LCD, MAX31855K, Arduino Nano

apparentvjapparentvj 11/16/2016 at 17:370 Comments


This being the first log and the project is ongoing for some time, I'll put here all the works until now.

As we know the internet is full of toaster reflows, I've gone through most of them for inspiration. But none of them were matching my components, necesities or taste.

So, same story, made my own.


Everything started with the Smoothieboard, it's a great! 32bit CNC Controller.

But price was preety high and thought, for that money I'll make my own reflow oven, buy components, PCB's and learn a lot along the way, as already wanted to get into surface mount components.


Oven. I bought a cheap oven Severin TO , but was really scared that it wouldn't heat up quickly enough, having ~1500W @220V and 19 Liters. But after purchasing I saw EEVBlog's video about SMD Reflow and saw the same Oven from a BetaLayout Kit. Good, that was a relief, now I'm assured it works reliably.

Thermocouple. Saw that everybody is using MAX6675 or AD595 these seemed preety outdated components and you need a lookup table to convert current to temperature. Wanted something new, that will last and the project will be easily maintanable in the future.

Went with the MAX31885K, but as the chip in my country was more expensive that the ThermoClick from Mikroelektronika bought from farnell. (Bastard romanian resellers)

Relay. Bought a chinese 25 A "FOTEK" Solid State Relay . As we'll be using around 6Amps, I'm not really scared that'll blow up any second. Got a big heatsink with a fan from an old computer, that'll do it. As the Arduino isn't powerful enough to trigger the relay I'm using a BC547 NPN transistor to switch the 12v rails to the relay (as shown in the diagram).

Arduino. As I wanted to integrate it into the assembly, I've choosen the NANO.

Screen. Got some cheap mcufriend 2.4" TFT LCD + rotary encoder

Parts. On/Off Switch, E-Stop Button, 12v Transformer, StepDownConverter12v-5v


Started with dismantling the oven to pieces, as I wanted to reassemble it with screws and insulation. Ripped it's guts out, and found out the old wiring was switching the Neutral so Live was always in the heating elements. As insulation between walls I used black Gasket Sealer. Then after letting the silicone cure, I insulated the walls with mineral padding (recovered from and old oven) as you can see in the pictures.


Preety straight forward, but unfortunately I found myself using all of the NANO pins and don't have space for functionalities I wanted to implement. So future version will have a shift register to broaden the I/O.

Schematic coming soon, and a diagram of the whole electrical wiring.


Right now I'm finishing the software side of things, the sketch is around 1K lines including comments. Right now everything is on a breadboard, but plan to put everything on a pcb.