Sous PIDe v0.1

I've wanted to build a PID temperature controller for a while. It's essentially an intelligent thermostat that carefully maintains the temperature, with a low hysteresis and minimal overshoot. They're used for all sorts of things, like sous vide cooking, brewing, reflow solder ovens, basically anything where accurate temperature control is required.

I've recently done some experiements with Retrobrighting (bleaching) old discoloured ABS telephones. The original method involved using a source of UV, such as the Sun, but more recently people have had good results using heat, which finally gives me an excuse to build a PID temperature controller.

This post isn't a detailed tutorial. Just some food for thought if you're constructing your own.

 

Sous PIDe - A PID based temperature controller

 

 

I purchased a combined bundle of the REX C-100 PID controller, a FOTEK 40A Solid State Relay (SSR), a heatsink, and a short thermocouple came to the grand total of £13.26 including P+P & VAT from AliExpress. The REX controllers are known to be cheap and do the job, but it sounds like they have quite a high failure rate. This might be an issue if you're controlling the temperature of something that'll be expensive if it goes wrong, but for a basic proof of concept it should be adequate.

The PID Controller is mounted in some laser cut and folded 3mm acrylic sheet - I'd share the design but I don't recommend it, it was a total faff bending the plastic without warping other areas. If you're desperate for it get in touch.

 

Despite its appearance made some effort to make it safe, such as putting acrylic covers over exposed terminals carrying mains voltage. They'll stop an accident like a dropped screwdriver shorting something out, but they won't stop you sticking said screwdriver in a live terminal - some common sense is required and I wouldn't recommend using it in the prescence of children, animals, or anyone daft enough to take a screwdriver to it whilst its plugged in. I've also bonded all exposed metal parts to earth.

 

I've still not quite mastered tuning the PID controller. The auto tuning wasn't great (Another known issue) so I have to dial in my own values for P, I and D. I'll probably have to build an external temperature logger in order to perfect it.

 

 

Sous vide eggs anyone?