8 April 2014 – When we assemble prototype PCB’s in the lab using SMD components and solder paste, we use a normal desktop oven to reflow the boards. In the beginning we used a TV-braai – well, that’s what we call it in South Africa –  and just eye balled it till we guessed it was cooked enough! Surprisingly I have built quite complex PCB’s using this method with a great success rate.

 

After a while we decided to hack an off-the-shelf oven and add some form of temperature control. We did this by ripping out some of the internals and controlling it with a relay and thermocouple.  This has been working perfectly for a few years except for the unsightly project box and wires protruding from the oven. I always wanted to make a dedicated PCB to control the oven and finally made the time to do it. The following was on my wish list:

• Minimal hacking of the oven.
• Safety.
• Hacker friendly (Arduino™).

I decided to us a fused opto-isolated triac circuit capable of driving a 3000W oven. Added a MAX31855 thermocouple-to-digital coverter and added a piezzo buzzer, RGB LED, fan output and a connector with inputs for 3 push buttons. The smallest panel mount connector I could readily and cheaply find was a standard DB connector and used a Degson power connector for the AC line. The idea is to place the oven controller inside a project/laser cut box. Fit a panel mount AC socket to the side of the box where the oven can be plugged in using the plug which it came with. The oven can then be controlled using any micro controller of your choice such as an Arduino™ via the DB connector. The thermocouple can be inserted into the oven via the door or you could drill a hole in the side and mount it properly. I should mention a thermocouple in free air usually reads lower temps than the actual PCB because the PCB absorbs the heat better than the air and you should calibrate for this. Another option is to temporarily fix the thermocouple to your PCB with a paper clip but I find I never have space for this.

Here are some photos of the finalized PCB:

 

We have extra PCB’s available and will sell them as blanks, populated or in a laser cut enclosure. Give us a shout if you are interested.