Yay! I just rewired the oven in parallel, so now it has 3200W. It heats up to 250°C in about one minute (4°C/s)! That's more than enough! Now the software has to do it's job and it has quite big reserve.
Just a quick update : made the PCB. Only 1 unrouted wire left (as always), but I'll fix that in no time this time :D New PC arrived (I'ts a laptop, I've never had a laptop!) and I'm excited because it is even faster than my old overclocked i7. Also the oven has been sent by the seller yesterday, so I'll expect it to arrive today or tomorrow. I have two syringes (extra small ones, about 2 grams [fraction of ounce - how much is the ounce btw?], only for tests) of soldering paste, so I'm ready. I bought both leaded and unleaded, because I don't know if the oven will manage to heat to 250°C although it is advertised as so (unleaded paste requires higher temp).
Day 8: Now, that the prototype, and firmware works, I did the schematic and started to route the board (that was the night before). Tonight I'll try to finish the board. Since I do not do PCB by myself (mostly because I have 3yrs kid running around, and I don't want that he drank iron chloride, whether accidentally or on purpose), I'll have them fabricated by some local fab. Oh, and seems that the hackaday.io profile is invisible. I know that this kind of oven stuff may be boring, but I thought there are more bored people / hobbyists outside.
Had a few problems, but firmware is more or less complete. It is as simple as it only could be. Got the casing and it seems to be to small to house the small PSU which would power the relay (relay is opto-coupled from the logic, and logic is powered from the USB) thus I'll go with external wall-wart, oh well. Tonight (when kid go asleep :D) I'll try to sketch the PCB.
After few hours spend on reading about control theory and PID controllers in particular I came to the conclusion, that PID controller is not suitable for my oven project mostly because it's on/off device. Although you can set temperature on most ovens, there is no simple way for me to control the knob on the panel - this is obvious. So instead SSR (a relay) is used, transforming the oven into on/off device. In a PID controller I is used to speed up the process increasing the overall value (lets name it u, where u = P + I + D). So lets assume, that setpoint (SP) equals 100°C, and PV (actual temperature) equals 20°C. Thus the error (e) is 80, and hence P > 0, the u becomes 1, oven starts to heat up. I increases every Dt (delta t), because it accumulates the past errors, but heating cannot be speed up : you cannot turn it on more. Similar consideration goes to D.
So for now I think, that the best solution will be to implement a on/of (bang-bang) controller with deadband (deadband dependent on thermal capacity of the oven used).
Day 5: Implemented P.I. controller (rudimentary). Successfully achieved 100°C without noticeable oscillations, but this is due to the fact, that I am using small toaster which has very low thermal capacity, and heats up almost instantly (and cools down fast).
Day 4: USB control requests are working as expected. I like them because they maintain data integrity i.e. each request has its own name (number, and 2 additional words) and it is apparent what it's doing. In my case there is only one request "GET_TEMP_REQUEST" (check GitHub) which sends back 32 bits of thermocouple data to the host. The highest measured temperature of light bulb in my desktop lamp is : temp = 274.75°C. It's 1AM, and I must wake up at 6AM o'clock. Oh well...
Day 5: Added the relay. Lesson learned : beefy solid state relays won't work with little load. My works when load has at least 24V and 50mA (or more ?). So I quit supplying 5V and other funny voltages, and went with 230V AC. Little scary, but at the end it would operate with high voltage, so what the heck. So tonight I basically made 100W blinky :D Also, tested the thermocouple with toaster, and it peeked at about 200°C.
Day 1 : MAX31855 testing with TM4C123 launchpad if I remember correctly. It was a while ago. Data acquired via USB.
Day 2: MSP430F5529 firmware (basics). Added URL.
Day 3: µC and thermocouple ADC see each other. Raw data (32 bits) is being sent to the host via USB CDC class connection. Tomorrow I'll try to switch to clean and tidy USB control requests, and maybe make some piece of host software to visualize the temp. readings. There's not much time left, in week or 2 all pieces of CPU-gauge will arrive and I want to solder the thingy in the oven (don't have the oven itself even!).