This Fail of the Week will remind our readers that every project they make, no matter how small they might be, may have big consequences if something goes wrong. Shown in the picture above is an oven that [Kevin] tweaked to perform reflow soldering. The story is he had just moved into a new place a few weeks ago and needed to make a new batch of boards. As he had cycled this oven many times, he was confident enough to leave the room to answer a few emails. A few minutes later, he had the unfortunate experience of smelling something burning as well as discovering white smoke invading his place.
The oven control board [Kevin] designed is powered by USB and uses simple ON/OFF temperature control. The temperature inside the oven is measured using a MAX6675 K-type thermocouple amplifier. After having thrown the oven outside to contain the risk and let it cool down, [Kevin] started to investigate what may have been the cause of the incident. He discovered that his temperature reading was not correct, and that swapping the USB AC adapter with another resolved the problem. The chip reading the thermocouple needs a solid 5V reference for accurate readings. The mains adapter he was using is non-branded and he guesses that the 5V rail is super dirty. We’d love to see an oscilloscope screenshot… perhaps encouragement in the comments section will convince him to publish a follow-up?
He plans to implement a simple over-temperature detector on a completely separate circuit using a mechanical relay to cut mains if things heat up too much.
Fail of the Week is a Hackaday column which runs every Wednesday. Help keep the fun rolling by writing about your past failures and sending us a link to the story – or sending in links to fail write ups you find in your Internet travels.