Adam Haile wrote in to share about his Dial-A-Song project — in order to create a matrix keypad Raspberry Pi interface he had to write a new library around interrupts instead of polling (here!) that he wanted to share. “I’m using an old phone keypad here but it works great with your membrane 3×4 keypad equally as well.”
Here are a few details from his ongoing Dial-A-Song Voicemail Musicbox Project:
Much of the inspiration came from They Might Be Giants, who used to leave recordings of their songs on their answering machine, which could be listened to by calling (718) 387-6962. So, I wanted to combine a little of that with a phone tree menu to give the feel of calling in to a phone service to listen to music of your choice. Yes, it’s a little ridiculous, but why else would I be building it.
As a way of documenting the project and an extra push to keep working on it, I’m going to be writing up a build log in several parts as the build progresses.
…The first thing to do was remove the short ribbon cable that came on the keypad and replace it with something a little longer so I could more easily hook it up to the Pi.
…It’s super simple to use as you can see from the code below. Instantiate the class with a callback function and that function gets called when there’s a keypress on the pad. Just note that the callback will be running on the context of a different thread from the main thread. While it uses interrupts, RPi.GPIO cheats a little bit and the interrupts are actually running on background threads and so will the callback. Not usually a big problem but something to be aware of.
You can grab the full library and find any updates to it on GitHub.