A PIC Based Temperature Controller – Part 4
I have a basic user interface setup that allows the temperature to be set. Currently only the right 2 buttons are used, one for up temperature and the other for down temperature. When the laminator is turned on it shows the current roller temperature. Pressing the up/down button momentarily shows the set point, which is 50F at power up. This means the laminator is off by default. Holding up/down for a couple seconds starts the temperature changing in 5 degree increments every second. Releasing the button again shows the actual temperature of the roller.
I plan on adding code that will use the extra button to allow the set temp to be saved to the PICs internal EEprom and set again just by hitting the button momentarily. This will allow a commonly used temperature to be set quickly. Also, the room temperature calibration will be entered by holding the 3rd button while powering on the laminator. The calibration will also be saved to EEprom, and will only need to be done once. After working with the the code, I also want to a feature that will allow the PID constants to be changed by entering a special mode. This will allow the board to be tuned for different uses without needing reprogram the PIC.
I have tried the laminator out at it works well. Here is a picture of the laminator heating up. Please ignore poor quality, I had to do a longer exposure because I was only getting one digit showing in the pictures. This is caused by the 3 digits being multiplexed and only a single digit being turned on at a time. The camera was fast enough to only show one digit on at a time.
I currently have the second sensor disabled, because the PID control loop does a good job heating up the laminator while preventing overshoot. I will add the second senor as a fail safe that will turn off the laminator if the first sensor stops working for some reason. The laminator heats up to normal lamination temp of about 240F in less than 2 minutes. This is a nice improvement of the original 5 minutes or so it used to take, and is an added bonus of the modification.
I ran a blank board through a few times and the laminator only lost about 15 degrees on the first pass and recovered quickly. After the 2nd pass the board was hot enough that I didn’t want to touch it. This is a big improvement on the dozen or so passes it used to take. I need to see how hot the laminator will safely work. I have tried 260F for about an hour without any issues. If it can go a bit higher, a one pass toner transfer should be in sight. Worst case it will take 2 passes, which for me is very acceptable.
The display cutout was just done with a rotary tool, and while being a bit crude, works well. If I left the bit of plastic that would have gone between the display and buttons it almost would look stock.
Seeing there might be some interest in this project, I have set up a kickstarter page to try to get this into the hands of hackers and tinkerers like you. If you are interested, please feel free to check it out.
I hope to post a video of the laminator in action soon, but it’s currently apart as I was adding some features to the code.