The Project

After finding an old hotplate in the basement, and remembering the trouble I've had with flat no-leads packages, I decided to retrofit the hotplate with a modern control system. The modern control system has the added benefit of allowing the hotplate to follow heating profiles I set up for it, such as those recommended by manufacturers for integrated circuits.

The Design

Why Smart?

You may be wondering why the hotplate is going to be a "smart" device, it probably seems as useless as a smart toaster, however I have some fair reasoning behind it;

• If I wanted to program a heating profile easily, I would need a display capable of displaying the curves, and all the displays I found weren't cheap.

• Further compounding the display price issue, the display will be right next to a hotplate, in the event of an accident, I would rather not have to replace the display

• I had a NodeMCU laying around and they're pretty cheap

However, to boost the ease of use and functionality of the hotplate, I will also have a basic display on the front and some controls for times where I just want to set the temperature and forget.

Board Design

Being the third board I've designed, and the first with high voltage, I am still a bit of a newbie at this, so any feedback is greatly appreciated. The board is essentially split into four sections, high voltage TRIAC and triggering, voltage step down and rectification, control and feedback circuitry and a separate display board. The high voltage section is controlled using optocouplers to protect the low voltage DC parts of the board. The final circuit schematic is shown below.

Progress

Currently, the project is waiting for parts to come back into stock, however in the meantime, I've assembled what I could, shown below, and intend to do some testing before I plug it into 120VAC. The display portion won't be functional for a good deal of time as the integrated circuit isn't expected to come back into stock for a long time, thanks COVID.