Because the principal thrust of my work over the past 40 years has been proof-of-concept, I have a considerable assortment of development boards on hand. I'm sure one of the simpler ones will do the job. I even have an 805x board with an LCD port and a number of other potentially useful features, one that I have in quantity because it's so cheap, came with a useful EPROM-monitor, and a small-C compiler, a FORTH interpreter, and an assembler, not that I've used those particular ones, and to which it's easy to attach other hardware, all for just under $40. It's not popular any longer, but still does what it always did, which is run 805x code. That one may, in fact, still be on the market.

I also have a supply of solid-state-relays for 110 volt AC control. I don't think I'll have to buy much hardware. It's just the packaging that always becomes bothersome when one builds rather than buying something of which only one is needed. When I need half a dozen or so, it's worth constructing holding fixtures, templates, patterns, etc, but with just one ... well ...

With a small CPLD, it's trivial to construct memory-mapped I/O locations, and once there's a place to put things, e.g. the CPLD, located on the protype area, that's as good a way to do things as any. However, I'd much prefer to buy something proven and well-specified, rather than trying to build something.

That doesn't rule out building the controller, it simply means I'd prefer to buy one. If I build one, I probably will simply use one of the many MCU dev-boards I have on hand. There's one really old 'HC11 board I'm considering, that has an 8-channel multiplexed ADC, which would work for temperature sensing, among other things, uses SPI to "talk" to peripherals, and has on-chip EEPROM for parameter and history storage. I haven't yet written 'HC11 code for the LCD, but I believe the LCD is probably the easiest way to display what's going on. I also have small SiLabs boards that have both ADC and DAC, if that should prove necessary, not to mention a set of comparators, which also might be useful. I doubt I'll have to find any more dev-boards.

RE