A digital tally list for hackerspaces

I'm a member of an open workshop in my hometown. Last week we started joking around about getting a drink vending machine. Still half joking, I started searching on eBay for used vending machines. While on my way to a pub, I pictured having a vending machine for the workshop: cashless, probably driven by Stripe.

While at the pub, my idea was quickly voted down. Instead the idea that gained traction was a digital tally list. We started sketching out this plan. It would be driven by the same RFID tokens that give you access to the workshop. We were unsure about having a prepaid or a postpaid model.

This problem looked like it was sized in a way that we could clear out the major road blocks during my vacation last week. The pub appointment was on Tuesday, I started work on Wednesday and had some basic demo running by the end of the day. I continued on Thursday and had more features and a more streamlined UI by the end of the day.

On Friday I slapped a license on it and evaluated our RFID options. Basically the RFID token we use as a key supports the MIFARE protocol, so we can go with the cheapest reader hardware that is available at 5 Eur a piece. Right now we're still in a state where we enter a UID on the command line, when prompted, instead of running with the actual reader. But the prompt is already running in its own thread and I'm pretty sure we can just connect the RFID reader in this way.

On Sunday a very talented friend joined in and he re-styled the entire app
with the workshop's corporate design. Simplifying stuff on his way.

Overall our plan is to write a digital tally list in two weeks, going from idea to running prototype. This tally list should support donations with a variable amount, drinks with set price, as well as assorted items like the workshop fee. It also needs to support rudimentary user management and some kind of admin interface. All users will be verified by RFID.

Currently consumption is logged into a monthly log-file, so we can easily handle the payments. Users are managed by the UI itself, we just have to put the initial UID into a json file. Drink prices are read from JSON and a price update requires a restart of the app. The app itself will run on a Raspberry PI with an attached 7" display and an RFID reader attached via the serial port.

The entire app is written in Python with a QML frontend.

I'm ordering the RFID hardware and the display this week, so we have a full weekend of hacking ahead of us.

Here we go.

Let's see if we make this.

Code lives here