The DeLonghi oven model I bought was the AD679. I bought it a little over a year ago at an online store as a sale item for about $100 but I don't know if they still make it. It's probably a little "high end" for stripping down (it's one with a digital temp control) but that actually came in handy for hand timing some boards. I seem to recall they made one with a mechanical timer and temp control that had the same heating elements and fan that might be more budget oriented.
My thoughts on how I'll probably implement my controller (and a few comments on yours too I guess):
1) I'm making my controller stand-alone. I'll let it interface to a PC, download profiles (probably save them to EEPROM/Flash on controller), upload real-time temperature and other status data and probably be able to run a real-time profile graph. But I definitely want to be able to have a profile loaded in the controller and just hit a "go" button and have it run a cycle.
2) I don't trust a PC not to crash in the middle of a soldering cycle. Considering how much time I spend on the prototype board if I burn a batch because @#$% Windows locks up or the program crashes, well... I'll not be a happy camper.
3) Type K Thermocouples are good. I was looking at Omega's website and they have some cheap Type K's. They also have some armored sheaths for mounting them that will help protect them. You just drill a hole on the side of the oven chamber and they bolt through. My oven already has one of these in it for it's temperature probe. I'm not sure if they used a platinum RTD or thermocouple, but I'll find out when I tear it apart. I'm thinking of running two thermocouples for above and below board temperatures.
I'll likely use MAX6675 converters for my thermocouple interface. I've used these before and they are sweet! The MAX6675 chip, a bypass cap, your Type K TC and you get 12 bit temperature over SPI (0ÂºC->1024ÂºC). I'm normally not a huge fan of Maxim, but in this case it's a great part for the job. Maxim's chips are great but getting them in production volumes for commercial products is always a crapshoot.
4) I'm definitely using keys and an LCD. I want a standalone user interface and display. In your case, why not just use a larger PIC? You seem to have a certain affection for 16F88's...
Which is fine, they're great chips but I've always believed in using the chip that fits the job not fitting the job to the chip.
5) I'll probably use solid state zero cross relays instead of mechanical relays. Mechanical relays can cause noise problems on the AC line, even when switching heavy resistive loads like the heaters. For the fan they'll be even worse. Mechanical relays will work but you may have to fight noise problems and the noise might even get back into the PC. But then I'm pretty conservative in my designs, especially when I'm building a tool I want to have work forever with few or no hassles.
Oh yeah, the toaster will probably have at least two relays in it (maybe three) -- one for the fan, one for the heaters or possibly one each for the top heater and botton heater. Hmmm, you know I don't remember my oven "clicking" on and off except maybe for the fan. They may be using triacs for the heating elements. I bet they are, they are cheaper than relays.
So with all that taken into account I still haven't decided which CPU to use. I have been doing a lot of MSP430 designs lately and really like the chip family. I'm a registered Microchip and Atmel consultant so I really should think about a PIC or AVR too. And I have an interface board
that I designed a while ago for the Rabbit CPU modules that already has everything I need except the thermocouple interface -- but it does have an expansion slot for a small board just for occasions like this. The Rabbit is overkill but probably easiest to write software for. And I'm a registered Rabbit consultant too... decisions, decisions.
Anyway, keep us posted. I'll do the same. I'm especially interested in what kinds of algorithms people are using for their heater control and profiling.