BitVend

Most recent code for each system is:

Arduino - Arduino/platformio/src/vend_hack.cpp RPi - RPi/bitvend/ (Rust service; RPi/bitvend/README.md explains the code, RPi/bitvend/SETUP.md covers setup). The old Python 2 scripts are in RPi/legacy/.

Docs for the vending machine itself are all in docs/ - CONLUX for the billmech, tcr6xxx for the coinmech, and the other two for the rest of the machine, including the control board.

System Overview

The original vending machine components all seem to work. The Bitcoin acceptance works by performing a 'replay attack' on the coin mech, the TRC6010. It communicates with the vending machine 'motherboard' via a 12-pin connector ( `./manuals/Vending Machine Manual w Schematic.pdf, page 40 / last page, connector J7).

This 12-pin connection has 3 main wires for communication between the two components; Send, Interrupt, and Data. These wires seem to be running at 5 V. Note that these pins have two different numbers, depending on which connector you're referencing. In the trc6xxx manual, they are pins 3, 4, and 5 ( `./manuals/trc6xxx_operational_service_guide.pdf, page 10). But in the full Vending Machine manual, those pins are mapped to different pin numbers on the J7 header. Effectively, the wire ordering is 'shuffled' on the TRC-6xxx connector vs. the vending machine motherboard. I would recommend just using the pin numbers from the trc6xxx manual, but be very mindful of the actual pin placement on that cable.

For the 'replay attack', we previously recorded the timing of voltage state transitions on these wires when a quarter was inserted into the coin mech. These recordings are stored at the top of vend_hack.cpp.

The responsibilities of each component are:

• Raspberry Pi: Receive Lightning payments to a static address (Lexe wallet), convert each payment to USD, round to whole quarters, and pulse a GPIO pin once per quarter.
• Arduino: For each pulse from the Pi, grant one quarter of credit on the vending machine by replaying a coin signal recording.
• Vending Machine: Accurately list prices for items, and vend them. Can optionally provide change.

Electrical

You probably want to power the Arduino from the coinmech -> motherboard connector / pins. This is a simple way to make sure the Arduino is using a suitable ground reference. For the coinmech pins:

• Pin 10 is ground and pin 12 is 24V (high).
• Pin 2 does not seem to actually be tied to pin 10.
• Pin 1 is indeed 5V high.
• Pins 3, 4, and 5 are 5V, and held high by default.
• An Arduino Uno (or similar) can run off of the 5V power available on this connector.

There is an ON/OFF switch behind the bill acceptor; that is for the whole vending machine.

Accepting Funds

Customers pay over Lightning to a static Lightning Address / BIP353 address (₿name@lexe.app), shown as a QR code on the machine. The Pi runs RPi/bitvend, a small Rust service built on the Lexe wallet SDK, which:

1. Waits for incoming Lightning payments.
2. Converts each one to USD at the current BTC price (Coinbase, falling back to Kraken).
3. Rounds to whole quarters: down, or up if within 2% (2¢–24¢) of the next quarter.
4. Pulses Pi physical pin 12 (BCM 18) once per quarter; this pin is wired to Arduino pin 10.

The Pi holds only receive-only Lexe credentials; the wallet's seed phrase stays on an admin machine. See RPi/bitvend/SETUP.md for setup, deployment and tests, and Arduino/platformio/README.md for the pulse protocol.