Notice: This project is incredibly dumb both due to the fact that there are high voltages at play, but also because it has the potential to burn your house down and everyone in it. Treat this as a curiosity and don't try to replicate it.
The original plan for this project was to make a system to mix waste 3D printer filament that I could pour into moulds. I don't believe now that either maker is safe up to 200°C let alone the 250°C required for ABS as bread does not require that sort of heat. I purchased two bread makers from Value Village (aka Savers) for under $16 CAD total. One is branded as CounterCraft and the other is a Black and Decker model that was popular around the turn of the millenium.
All that said, having a temperature controlled mixer can have many uses. Including baking bread!
Internally, both are set up the same way:
- A triac to control the mixer motor
- A relay for the heating element
- A thermistor (more on this later) for temperature feedback
- A 5v logic board with an LCD, microcontroller
- A high voltage board holding a piezo speaker and the scary bits
Externally, both are a mix of polypropylene plastic and steel.
This model has less plastic in the critical heat path and has the thermistor mounted close to the mixing pan. It has a better bowl fit in general but I have never seen this brand of maker before and likely will have trouble sourcing new pans if something goes thermonuclear.
The important wires seem to be (where the black wire is pin 1):
- Thermistor
- Thermistor
- Heater (active high, 25mA draw)
- Unknown
- VCC (5v)
- Unknown
- Mixer (active low, 350mA draw)
- Unknown
- Unknown
One of those unknowns is the piezo and I'll circle back when I take the board off again.
I bought one of these RAMPS boards with a graphical LCD display years ago and decided this would be a good fit as Marlin is highly customizable and can be controlled from standard tools or an SD card.
After some experimentation it turned out that the correct thermistor seems to be #8 that is listed in Configuration.h as "100k 0603 SMD Vishay NTCS0603E3104FXT (4.7k pullup)". I haven't tested its thermal resolution at higher temperatures just yet, but it seems to align well with my meat thermometer up to 87°C
That was fine, but as the bed heater MOSFET on D8 switches to ground I cannot drive the heater relay straight from the board. Instead, I'll hack together a little perf board with a few components and tack them onto one of the AUX pins. The triac drive for the motor should work out of the box.
