Pneumatic Controller: Part 3

That’s right, Part 3! Take that, Hand Typing project!

You will not believe how simple the solution to my interrupt woes turned out to be. I tried the code again with the Timer1 Arduino library and was able to use timer interrupts and the LCD, but still couldn’t change the LCD from inside the interrupt. While looking online, I found someone saying how interrupts were disabled inside other interrupts, but you could re-enable them.

Now until this point, I had thought that interrupts were disabled just as a function of how they work, but it seems that they are only disabled with the assumption that if you wanted to stop whatever you’re doing to do the interrupt, you probably don’t want to be interrupted while in it. But in my case, I did so that I could print to the LCD.


That’s it. That is literally all I added to the timer interrupt function to make it work perfectly. It is frustratingly simple. Anyway, it worked.

Luckily (?), it still had some problems. The timer interrupt had some confusion with the scrolling and would sometimes, but somehow not always, print random characters all over and stop the flow of the program. Naturally this was not something I wanted.

I thought of two solutions. The first was to change from an automatic scroll to one that scrolled when a button was pressed, using an external interrupt. This was significantly worse for some reason.

The second way was to get rid of the interrupts entirely.

“But Ari,” you exclaim. “You spent so much time getting them to work. They were so special to you!”

That’s true, imaginary commenter. But an important lesson i learned about writing papers is to kill your darlings. As much as I liked having timer interrupts in the code, ultimately they made it more complicated and worse than it needed to be.

So what would I use instead of interrupts? Well, the normal way would have been to just check for scrolling every loop through this part of the code, but I hadn’t originally because parts of the code stopped and waited for input, which would leave a break with no scrolling. What I realized is that only one function actually used the scroll function anyway so all I needed to do was reorganize it to use a loop instead of waiting (for those who have used the Arduino LCD, it was a switch from waitForKey() to getKey()).

This worked and the program now scrolls lovelily (it’s a word, look it up). It even makes the program a bit faster because there’s no extra memory taken up by interrupts and libraries. Hooray!

Besides a couple of smaller changes, the main thing I did last week was to make a temporary assembly for the keypad/LCD. Until now I had been leaning the keypad as best I could but this got a little annoying. I couldn’t put the full assembly together because I haven’t decided how things will be stacked (probably: Arduino – Generic shield to make disconnecting the Arduino a one step process – All wires besides the LCD – LCD), so I taped them together as best I could.DSCN2071


The nice thing is that the keypad was built with a window for the LCD, so everything looks all neat and shiny. The text displayed is from the beginning of the setup and is asking how many pistons to use.

Things continue to go well with no obvious problems foreseeable. I hope to finish the debugging of the setup program this week and then start assembling/testing the actual pistons.

Until next time!



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