Sniffing Vending Machine Buses

Sniffing the Multidrop Bus


We’ve talked about a variety of protocols and how to deal with them in the past. Today, [Dan] is working on sniffing vending machine Multidrop Bus. The Multidrop Bus (MDB) protocol is a standard used in vending machines to connect devices such as currency collectors to the host controller.

To connect to the bus, interface hardware is required. [Dan] worked out compliant hardware and connected it to an Arduino. With the device on the bus, [Dan] got to work on an Arduino sketch to parse the MDB data into a human-readable format. With that working, the bus can easily be sniffed over the Arduino’s serial console.

This is just the start of a more involved project. Since this protocol is used to communicate with a vending machine’s currency collector or card reader, being able to communicate it would allow him to implement his own payment methods. The plan is to augment the vending machine he operates at Vancouver Hack Space to accept Bitcoin. We’re looking forward to seeing that project unfold.


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