The makerspace I'm a part of had a community event pre COVID where we opened our doors to the public for prospective members to tour our space and meet our members too. It was a great time where a lot of people got to meet others and discuss projects and ideas too; there was a lot of creativity and fun on those nights.
Unfortunately, for a long period of time that event was put on hiatus because of the pandemic and our poor case numbers at the time. It was really unfortunate since it really felt like a large part of what makes our makerspace welcoming and unique. Now with vaccines and other mandates put in place, we're able to open our doors and have our open night again; just with a few small changes.
I wanted to make something unique for the reopening, something shows off the skills I learned at the makerspace and my own skills in design too. I thought a wearable nametag would be perfect for that, and a wonderful conversation starter too. With that in mind, I set out these goals
- Wearable and battery powered. It can't be too big or too heavy
- It needs to be aesthetic to draw attention and be easy to read and know what it is
- Easy to make and accessible, especially if other members want one too.
For my first prototype, I chose a cheap MAX7219 clone module from Ebay. It'd give me an idea of how much current it could potentially draw, along with how many LED matrix I should use for something wearable. To control it, I settled on a ATtiny 45, which is becoming one of my favourite ICs! While it may not be feature rich, it can absolutely work with the simple serial connection the MAX7219 needs. The code running on the device isn't mine, and all credit goes to Electronoobs' example on scrolling text. His work is elegant and efficient, and easily fits within the 4kb of program space my MCU has.
The next consideration was how to make something wearable. Obviously that meant the project needed to have a small and dense battery like a lipo pack and a way to charge it too. I've done this a few times before, and it's incredibly easy with something like the MCP73831. There's one thing little difficulty though. The MAX7219 asks for a minumum of 4v, which is higher than the 3.7 nominal voltage a lipo battery can provide. I need to source a boost converter circuit that can supply up to 500mA. The PAM2401 seemed like a suitable IC for my needs, it's well documented, has a small footprint, and only needs a few passive components to work.