When the weather is too cold I can’t etch because the etching fluid freezes. So I made a heated etching tank, the heating element is recycled from an old washing machine. It consisted of 2 heating elements, a large 2Kw and a smaller 1Kw, I cut the 2Kw off so it would fit in my tank (and 3Kw would be too much). 1Kw is still a lot off power so I put a dimmer on it. To regulate the temperature I made a temperature controller with a pic16f676. The temperature sensor is a LM35 with heat shrink around it. The display is a 2x7segment display (Datasheet).
The hex file for the pic can be found here: Link.
The pcb (PDF):
The triac broke becease my heating element pulls almost 5A and the triac is a 4A model. Therefor I replaced it with a BT139 tricac.
I got a few questions about my etching tank, so I decided to take some pictures:
The etching tank is build from 2 ice-cream boxes:
The bottom box is filled with water, so the etching fluid heats "au bain marie".
To keep the etching fluid in movement I made a stirring machine from an old walkman and a handyvac.