Bitcoin Point of Sale System
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This is a Bitcoin point of sale application. It was mainly written to demonstrate the use of the green address feature, but can also be used independently of that. It is written in Python and works in combination with the standard Bitcoin-Qt client. It is targeted at standard PC hardware, e.g. laptop (used by merchant) + external monitor (facing the customer). The main mode of operation is displaying a QR code with a Bitcoin URI to the customer and listening - via Bitcoin-Qt - on the network for a matching Bitcoin transaction. But the software also support the use of NFC hardware to transmit the Bitcoin URI as well as receiving incoming transactions via Bluetooth. See videos of the system in action at (using QR codes) and (using NFC).


Getting started

The system requires at least Bitcoin-Qt 0.8.2, as it is making use of the 'walletnotify' feature. To check for green addresses a complete transaction index is also required, which can be enabled by adding 'txindex=1' to bitcoin.conf and starting the daemon with '-reindex' to build the index the first time. The configuration file ~/.bitcoin/bitcoin.conf should look something like this:


Then start bitcoind like listed below (-reindex is only needed on the first run). Make sure that the queue-tx utility is executable, so that bitcoind can call it when new transactions are received.

./bitcoind -reindex -walletnotify="/path/to/greenaddress-pos-tools/utils/queue-tx %s"

Afterwards you are ready to start the Python app:

  • install dependencies: python-bluez, python-qrencode, python-qt4, python-zmq
  • create the file $HOME/.greenaddress-pos-tool with this contents (or let the app create this default configuration file when first starting up):
    "exchange_rate_ticker": {
        "currency": "USD", 
        "fields": [
        "interval": 60, 
        "source": "", 
        "url": ""
    "green_addresses": {
        "1LNWw6yCxkUmkhArb2Nf2MPw6vG7u5WG7q": "Verified by Mt.Gox.", 
        "1MAxx46Dp3tFw933PxPwEYYGCpxYda2pyH": "Verified by Bridgewalker."
    "rpc_url": "http://rpcuser:rpcpassword@", 
    "single_screen_mode": false
  • run: python

You should see two windows popping up: The merchant back end and the customer display. If you enter a BTC amount and click "Update display", a new Bitcoin address and associated QR code will be generated and displayed to the customer. The tool then listens for transactions to the Bitcoin address and as soon as it receives something, it changes the display to read "Payment received". If the payment was done via Bridgewalker's green address, it will add the phrase "Verified by Bridgewalker". The merchant is expected to use their Bitcoin client to see if the correct amount was sent.

NFC support

The software supports the use of NFC hardware. If an NFC device is detected, it will be used to offer the currently displayed Bitcoin address and amount to any client that comes within range.

Any device supported by the library nfcpy ( ) should be fine (see ). This code was tested with the NFC reader 'SCM SCL3711'.

To get this reader running on Linux, you need to ensure that the permissions are set properly. You might want to create udev rules like the following (e.g. as /etc/udev/rules.d/52-nfcdev.rules):

SUBSYSTEM=="usb", ACTION=="add", ATTRS{idVendor}=="04e6", ATTRS{idProduct}=="5591", GROUP="plugdev" # SCM SCL-3711
SUBSYSTEM=="usb", ACTION=="add", ATTRS{idVendor}=="054c", ATTRS{idProduct}=="06c1", GROUP="plugdev" # Sony RC-S380

Load the new udev rules via 'service udev reload'. Afterwards make sure, that you are a member of the 'plugdev' group, to be able to access the device. You might also need to prevent the kernel module 'pn533' from grabbing and blocking the device:

rmmod pn533
echo "blacklist pn533" > /etc/modprobe.d/blacklist-nfc.conf

The following clients are known to be able to receive Bitcoin URIs via NFC: Schildbach Wallet, Bridgewalker.

Bluetooth support

The software will use Bluetooth to listen for serialized Bitcoin transactions. To this end, it will advertise a Bluetooth service using the UUID 3357a7bb-762d-464a-8d9a-dca592d57d5b (compatible with Schildbach Wallet and Bridgewalker). It will furthermore include its Bluetooth MAC as an additional parameter in all Bitcoin URIS (&bt=...). Clients that support this convention can then transmit a serialized Bitcoin transaction via Bluetooth using a simple format first specified by the Schildbach wallet.

The following clients are known to be able to transmit Bitcoin transactions via Bluetooth in this manner: Schildbach Wallet, Bridgewalker.

Green address technique

You can read more about the green address technique in this thread: or on the wiki: . Currently (as of June 2013) Mt.Gox and Bridgewalker ( ) implement this convention and allow to send transactions that will be recognized by the Python app as originating from a green address.


I'm developing on Linux, so this is only tested on Linux. But I would hope this to be fairly portable. Patches to make it work (better) on Windows and/or Mac OS are welcome.

If you appreciate this release, donations are gladly accepted at 1CQoprPjRmsDQDzgmUK1njmXSv3SMpAjm7 .