So, the smoker project is progressing. There I was, happily adding features (like supply voltage monitoring) and then it happened – out of memory.
I’m using a Microchip PIC 16F886 microcontroller that has 8192 WORDS of memory. In case you’re not sure what that means, a word is two bytes – so it has 16K of program memory – LOTS of memory, right? Well, apparently not.
Now I have a dilemma – I was still going to add serial and wireless communications to it so it could notify me via text message if anything bad is happening. That’s not going to be happening with the current board I have. So, here’s what’s going to happen – I have stopped adding features, and will concentrate on getting the ones I have working properly. At that point, I will work at making sure the PID process control routines are tuned perfectly, and I will have a complete, working, charcoal smoker temperature controller,
Next winter, I will have a new version of the board that uses a PIC 18F2550 microcontroller – one that has 32K words of memory – more than enough (yeah, right, I said that about the 16F886!), Below is a screen shot of the new design – all through hole except for the resistors, they are SMD on the underside. I think I will make this board all SMD when I get around to making it.
Oh yeah, the voltage monitoring – when I designed the V1 board, I included a voltage divider that goes to another ADC channel on the microcontroller. A little bit of programming, and I am able to sample and display the supply voltage within 100 millivolts – more than accurate enough. The user can press a button in auto mode that will display the voltage for five seconds, and the supply voltage is being checked twice a second during error checking. If the voltage drops to 10.5Vdc or lower, the fan and solenoid are powered down and the unit starts beeping an error. On the display, the user is prompted to turn the unit off and change the power supply. When it powers back up, a status bit is read in the on-board EEPROM that bypasses the title screen and setup for that power-up only. It goes directly back to Manual Mode so the smoker doesn’t get out of control.
The reason for this is that smokers sometimes get used where there is no Hydro – no power to run a power supply. A battery is the only option, and some of those BIG pork shoulders take many hours to cook. Just a way of ensuring that everything is working well.
There are still a couple of glitches to clear up and I’m ready for BBQ season! Now if only the 6ft of snow in my yard would melt!