This is a collection of bits that allows a device to communicate with a vending machine that implements the MDB/ICP standard.
At SparkCC we have a bunch of vending machines. Of these, at least one talks MDB/ICP, which is a protocol that connects a VMC (vending machine controller) to a number of devices, like coin mechs, bill acceptors, and cashless (credit card etc) devices. There's been a long-standing project idea to actually use this vending machine, probably for common components for projects, but managing money is a lot of effort and we could do it another way if we had the interface.
So. I'm building one.
There's a lot of info floating around about how these things work, but I wanted to learn how to do a heap of things, so I'm building it from scratch instead.
The biggest complication for this interface is the electronic interface - an opto-isolated multidrop serial bus isn't a big deal on its own, but finding a UART that supports 9-bit communications is a little less straightforward. A lot of microcontrollers have these, but then we want to hook the vending machine to more powerful systems so we don't have to deal with low-level considerations when we eventually build something way more complex than it needs to be.
Many of the design decisions for this project come from the contents of my gadget bin, as well as my own abilities:
This project has a bunch of filters defined to keep the KiCad files as git-friendly as possible. To set this up correctly, run this:
git config include.path ../extra.gitconfigFor more info about the filters, see here.
Contains project global stuff:
Schematics and PCB layouts for the board that connects all of the pieces together. Uses KiCad v5.
MDB/ICP interface firmware for the Teensy. This acts as MDB Cashless Device 1 (0x10). Uses Teensyduino via PlatformIO, because the Arduino IDE is... weird.