I've made my own controller before. I designed it so it could be made on a single side PCB using SMT and non SMT components (so a reasonable soldering iron was enough).

Here is what I found:


- Dual layer boards are beyond peoples manufacturing capability
- Open source is useless if your target user can't make the hardware. Expecting them to take a dual-layer board design to somebody to cut is a stretch.
- Open source is useless unless your target can build the programming tools
- Thermocouples are prohibitively expensive due to the CJC circuitry
- Thermistors are cheap and work (albeit with more complicated software). But they are generally limited to -50C. i.e. only good for single stage controller.
- 4x20 Blue backlit LCDs look great

- Easier the assembly the more likely people will attempt it. (I designed mine with no throught hole, so no drilling required)


Without quantity purchasing I can't see you getting the price-point you suggest given the SSR's, CJC's, Thermocouples, op-amps going into your circuit.

You will also have to simply split the project into single stage or dual/multi stage controller. The specs are just to different.