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A decentralized DePin bar using Solana Pay Qr codes to buy drink directly from a bottle using a raspberry pi and a pump.

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LetMeBuy - A Solana powered Raspberry Pi drink dispenser

A decentralized bar system built on Solana that allows users to purchase drinks using USDC, connected to a Raspberry Pi that shows the product and plays a sound as soon as the transaction is confirmed, and also sends Telegram notifications to a channel for tracking sales and table deliveries.

Live Version of the app

Video Walkthrough

Table of Contents

  1. Demo & Media
  2. What You Need to Build This Project
  3. How it Works
  4. Features
  5. Quick Start
  6. Setup
  7. Manual Raspberry Pi Setup
  8. Development
  9. Contributing
  10. License
  11. Attach a bigger screen to show QR code
  12. Connect the Raspberry to mobile internet

Demo & Media

Here is a Video of how the bar looks like in action. And its not hard to build! https://x.com/SolPlay_jonas/status/1915380491852697746

shAkb6ywYxZAG63U.mp4
image

What You Need to Build This Project

Any of these different pumps:

There is some starter kits which contains the servo and some cables if you want to have some more options. For examples you can add a distance sensor, or some motor or something else to your bar project.

Optional:

If you want to show the current product on a screen or play a sound when a purchase is made you can add the following: I would also recommend one of the power solutions to power the raspberry pi and the pump so you dont neet to have it connected to a cable all the time. The X306 is a bit easer to setup and has more power. But the PiSugar is a bit smaller and cuter.

How it works

Best watch the Video Walkthrough for a detailed explanation. The heart of the project is the WebApp that controls an Anchor program which lets you create your own store where you can sell items via Solana Pay Transaction Request QR codes. The raspberry pi listens via a websocket connection to the Anchor Events that are emitted from the program whenever there is a new Purchase. When it finds a drink in the receipts that has not been delivered yet and fits its configured product it will press the button at the pump, deliver the drink and then mark the receipt as delivered via a transaction. The Vercel app also listens to a Helius Webhook that triggers an API every time there is a new Purchase anchor event and then posts a message into a Telegram chat.

Features

  • Purchase drinks using USDC or other SPL tokens via Solana Pay QR codes
  • Real-time product display on Raspberry Pi OLED screen
  • Sound notification on successful purchases
  • Automatic Telegram notifications for sales tracking
  • Multi-product support with configurable prices for any SPL token or SOL
  • Receipt tracking and management
  • Bar setup and configuration interface

Quick Start

Recommended: Use the install script in the raspberry folder to automate setup and configure the bar script as a service.

cd raspberry
./bar-install.sh

This will install dependencies and set up the Raspberry Pi service automatically. Best follow the tutorial in the README.MD in the raspberry folder. For manual setup, see below.

Setup

Hardware Setup

image

1. Connect the Servo to press the button. It will be controlled via GPIO 14

  • Connect the Brown cable to GND for example pin 6
  • Connect the Red Cable to 5V pin 2 or 4
  • Connect the yellow cable, control pin to GPIO 14 which is pin 8

2. Connect the OLED display:

A detailed guide on how to connect the OLED display to the raspberry pi can be found here

  • SDA to GPIO 2 (pin 3)
  • SCL to GPIO 3 (pin 5)
  • VCC to 3.3V (pin 1)
  • GND to ground (pin 9 doesn't work for some reason. Use another one, for example: pin25)

3. Connect DFPlayer Mini MP3

  • Follow the instructions here to connect the DFPlayer Mini MP3 to the raspberry pi

  • Put an mp3 file in the DFPlayer Mini MP3 folder on the sd card

  • Make sure the file name is "0001_YOURSONGNAME.mp3"

  • Make sure the file is in a folder called "mp3"

  • The red LED on the DFPlayer Mini MP3 should light up when the file is playing it will not light up all the time.

  • To test if the DFPlayer Mini MP3 is working you can connect a speaker and power and then connect the bottom right two pins for a short time and it will play the first song.

  • 3V to 3V or 5V Pin 1, 2 or 4 on the Raspberry Pi whatever you still have free

  • Connect your 3w Speaker to two speaker pins

  • GNG to any GND on the raspberry pi for example pin 34

  • The Trigger port 1 to GPIO 23 (pin 16) this one wil play the first song on the DFPlayer Mini MP3 card whenever a purchase is made.

image

Software Setup

You can directly use the bar at https://letmebuy.app/ you only need to deploy a new program and app if you want to do changes to the bar program or want your own unique frontend design.

  1. Clone the repository:
git clone https://github.com/Woody4618/bar
cd bar
  1. Install dependencies:
# For the web app
cd app
yarn install

# For the Raspberry Pi
cd raspberry
yarn install
  1. Configure environment variables:

The deployed bar already comes with a setup bot and you need to just add the LetMeBuyBot to your channel.

If you want to use your own bot you can create a telegram token by talking to BotFather. You basically just ask the botfather if he can create you a bot using /newbot and then you can use the token he gives you.

# Create .env.local in app directory
TELEGRAM_BOT_TOKEN=your_bot_token_here
RPC_URL=https://api.mainnet-beta.solana.com
  1. Start the development server:
cd app
yarn dev

The easiest way to deploy the web app is using Vercel

Deploy program

If you choose to deploy your own program. Just follow the anchor docs.

anchor test
anchor build
anchor deploy

Then you need to replace the program id in all places where it is used. Jus search and replace in hte project. If you change the program you also need to copy the idl into a few places. For that you can use the copy_types.sh script in the root of the repo or use the srcipt to figure out all the places where the idl needs to be placed.

Raspberry Pi Setup

For detailed Raspberry Pi setup instructions, see raspberry/README.md.

There is an install script in the raspberry folder that will install the dependencies and configure the bar script as a service if you want to automate the setup.

Development

The project consists of four main components:

  1. Solana Program (programs/solana-bar/):

    • Handles bar initialization
    • Manages product and receipt accounts
    • Processes purchases

  2. Web Interface (app/):

    • Bar setup and management
    • Product configuration
    • QR code generation for purchases

  3. Raspberry Pi Service (raspberry/):

    • Monitors receipt account
    • Displays product information on OLED
    • Plays sound notifications on receipts changes

  4. Telegram notifications:

    • Sends notifications to a specific channel when a purchase is made
    • This is done via a Helius webhook that calls the end point api/webhooktg
    • This api endpoint parses the anchor events out of the transactions and then uses the Telegram token to send a message to the channel that is configured in the bar setup

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is licensed under the MIT License - see the LICENSE file for details.

For detailed Raspberry Pi setup, troubleshooting, and advanced configuration, see raspberry/README.md.

Attach a bigger screen to show QR code

Having the QR codes printer and glued to the raspberry is cool. But also maybe a bit dangerous in case someone overwrites your QR code. So what you can do instead is directly show the QR code on a screen conneted to the Raspberry pi.

Some options for that would be:

I have not gotten the time yet to try these. So if anyone could provide the code for one of these would be awesome. Since these dont use the L2C interface we currently use for the smalle OLED display.

Connect the Raspberry to mobile internet

By default this project uses WIFI. But if you want to you can also connect it to 4g, LTE or Lorawan to work anywhere. Here are some options:

Use raspberry pi with a WIFI USB Stick

  1. Buy a sim card with data and activate it
  2. Buy a WIFI USB Stick. For germany i tested ZTE WCDMA Technologies MSM ZTE Mobile Broadband and it worked well.
  3. Connect the WIFI USB Stick to the raspberry pi via usb to micro usb and connect it to the USB port of the pi. Not the power port since that may be blocked by out power solution for the raspberry pi.
  4. In most cases it should be detected automatically and you can just use it.

Check if the modem is detected:

lsusb
...
Bus 001 Device 008: ID 19d2:1405 ZTE WCDMA Technologies MSM ZTE Mobile Broadband
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Then you can if the raspberry does atually use the modem:

nmcli device
...
eth0           ethernet  connected               Wired connection 1

It will most likely be showed as Wired connection 1. You can also check if the raspberry actually uses the modem using:

ip route

Use Raspberry pi 4G Hat

  1. Buy a 4G Hat. For example the Waveshare SIM7600G-H 4G HAT
  2. Connect the 4G Hat to the raspberry pi via the GPIO pins.
  3. Connect the 4G Hat to the internet via the sim card.

Use Lorawan

  1. Buy a Lorawan Devboard. I tried with the HTCC-AB02S and it worked well.

Check out the more detailed Lorawan README here

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A decentralized DePin bar using Solana Pay Qr codes to buy drink directly from a bottle using a raspberry pi and a pump.

letmebuy.app

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