Matemat

The Matemat is a vending machine for carbonated soft drinks.

It is based on an old vending machine with all its electronics replaced by new custom-build circuit boards.

All hardware and software was designed by members of CCC Basel and released in the form of circuit diagrams, printed circuit board layouts and source code for anyone to use and modify. Refer to the LICENSE file for details.

The name "Matemat" is a portmanteau of "mate" (as in mate tea) and "automat" (the German word for vending machine). The device is mainly intended to dispense mate tea based soft drinks, but may be used for other types of beverages too.

Structure

The heart of the vending machine is a Raspberry Pi model 3 or zero or later, with a custom CAN interface board on its GPIO header.

See CAN Hat for more information.

Firmware

Some of the modules require firmware. There is a makefile in each module's firmware directory to build and flash the firmware to the integrated microcontroller

Before building, you need to check out the CAN driver source code, which is referenced as a Git submodule.

Run the following commands in the checked out repository:

git submodule init
git submodule update

Modules

The Matemat components are highly modular. Individual circuits are connected by CAN bus, and can be extended as needed.

drive

Single-motor driver.

Attached directly to each bottle release mechanism. Requires only power supply wires for the motor and the CAN bus line.

power

Motor driver board and power supply.

Alternative to the drive board. Uses the existing machine wiring instead of power + CAN.

control

Old central control board. Obsolete.

feedback

End switch feedback interface.

Senses the status of the end switches and sends CAN bus messages on changes.

poweriface

Interface between CAN bus and power board.

This module requires firmware. Connect an Atmel programmer to the ISP header, change into the firmware directory poweriface/firmware/ and run:

make flash

sensor

Environment sensor interface.

wiring

Wring schema of the old vending machine.

Bus

Topology

All modules are connected via a CAN bus. It is highly recommended to wire them by means of shielded twisted-pair cable with a nominal impedance of 120Ω. At the very least, you need a cable with three wires to ensure a good ground connection between all modules.

To allow for easy wiring, six-pole screw terminals are mounted to the PCBs. Two poles are intended for the positive CAN bus line, two for the negative line and two for the shield. They are internally connected together.

Wiring

To achieve a continuous bus topology, connect only two cables to each module. Make sure CAN H is connected to CAN H and CAN L to CAN L. Crossover is not supported on the CAN bus. When wiring is complete, you should end up with a continuous bus that is tapped at each module. Attach 120Ω resistors (preferably 1% or better) to the ends of the bus.

The final wiring should look like this:

┌───────────┐   ┌───────────┐   ┌───────────┐
│  module1  │   │  module2  │   │  module3  │
│           │   │           │   │           │
│H L ⏚ H L ⏚│   │H L ⏚ H L ⏚│   │H L ⏚ H L ⏚│
└╥─╥─╥─╥─╥─╥┘   └╥─╥─╥─╥─╥─╥┘   └╥─╥─╥─╥─╥─╥┘
 ╰━╯   └╥┘╱      └╥┘╱  └╥┘╱      └╥┘╱  ╰━╯
 120Ω   ║╱        ║╱    ║╱        ║╱   120Ω
        ╚═════════╝     ╚═════════╝

Protocol

Bus communication only makes use of basic CAN features. No higher-level protocols such as CiA, EtherCAN, VSCP or similar are required.

Extended 29-bit CAN adressing mode is used.

This is the list of supported message IDs:

Message ID	Sender	Receiver	Data Length	Data Format	Description
0x1000	controller	poweriface	1	0b00000MMM	Start dispensing from slot M (0-5)
0x100	any	poweriface	0		Send power board status report
0x100	any	sensor	0		Send sensor board status report
0x10	poweriface	any	2	0xLL 0xHH	Power board status report (0xHHLL are the contents of the 16-bit shift register)
0x1	sensor	any	2	0bABCDEFGH 0b00000IJK	Sensor board status report (ABCDEFGHIJK are the states of the end switches, dispenser empty switches and the rest switch)