Fixing a 3-zone reflow oven with ATmega1280

Ed from over at ESTechnical owns a three-zone reflow oven. While the device had performed well for several years, like with anything, age took a toll on its belt speed and temperature control displays. Unfortunately, the speed became so inconsistent that most boards running through the conveyer weren’t completed reflowed. Meanwhile, the LCD displays were on their way out as well. Worst of all, the belt speed appeared to be varying with temperature. Since not a whole heck of a lot was wrong with the oven mechanically, in true DIY fashion, Ed decided to tinker around a bit to keep it functioning.

In doing so, Ed elected to remove the oven’s inner workings and swapping it out with an Arduino Mega (ATmega1280), thereby solving the belt problem and replacing the oven’s existing interface.

When Ed began looking into his belt speed problem, he discovered that the belt motor was controlled by an adjustable linear regulator and was completely open loop.

“I assume that as the temperature was increasing, so was the output voltage (some sort of power dissipation limiting in the IC?). I removed the conveyor belt drive motor and powered it up on the bench with a variable power supply. It didn’t sound good running with no load, lots of chattering of the shaft wobbling in loose bushings,” he writes.

After realizing that closed-loop speed control would really help make the oven more consistent, Ed decided to overhaul all of the electronics in the oven.

“To make the closed loop control possible, clearly a microcontroller needed to be involved in the new controller. I considered making a one off PCB for the oven, but rapidly settled on the idea of making as much use as possible of ready made prototyping stuff that’s widely available online. The Arduino Motor Shields seemed like a great time saver, and I found a range of screw terminal breakout boards with prototyping space for the Arduino family of boards.”

Upon determining that the new controller would be based on an MCU, Ed went on to substitute the temperature control and all of the functions of the oven with the ATmega1280 based board. The Maker also selected a breakout board for the Mega, a motor shield and a 4-input MAX31855 breakout board.

Upon completion, the Arduino now controls the belt speed and runs PID loops which drives the heating elements in each of the oven’s three zones. In addition, the ‘duino can be programmed with different profiles, stored in EEPROM, which are made up of three-zone temperatures and a conveyor speed.

Interested in learning more? You can access Ed’s detailed breakdown of the build here, as well as check out a writeup from our friends over at Hackaday here.