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Tunnel – Online payments for vending machine using Bitcoin from cell phones

Scenario details:

  • We have a vending machine for soft drink cans. Currently, the machine uses coins as payment, and depending on the amount inserted, the machine dispenses the corresponding drink
  • We want to incorporate an online payment system using mobile phones. For this we use Bitcoin
  • Each time a deposit is made to the Bitcoin address associated with the MTX-Tunnel, the modem will send a URC message via the serial port to the vending machine’s serial port so that it can count the deposit and allow the user to take a drink
  • The Bitcoin address associated with the MTX-Tunnel will be as follows: 
  • 1FTvXXEJCEFuRLe9A8ZZt2865KGiGet57r

Solution: MTX-65i modem + MTX-Tunnel software

EXAMPLE of settings (file config.txt) for such scenario:

COMM_baudrate: 9600
COMM_bitsperchar: 8
COMM_autorts: off
COMM_autocts: off
COMM_stopbits: 1
COMM_parity: none

MTX_PIN: 0000
MTX_model: MTX-65i
MTX_mode: none
MTX_ping: 30
MTX_urc: on

GPRS_apn: internetestatico.movistar.es
GPRS_timeout: 0

FIREWALL_enabled: off
TELNET_enabled: on
TELNET_login: user
TELNET_password: 1234

BITCOIN_enabled: on
BITCOIN_period: 30
BITCOIN_wakeup: on
BITCOIN_confirmations: 0
Serial port baud rate
Number of bits
No flow control
No flow control
1 stop bit
No parity
If SIM card doesn’t have PIN, leave as 0000
The MTX model chosen
We do not want GPRS gateways
Ping to ensure 3G/GPRS connectivity
IP to execute the ping
URC information messages enabled
APN GPRS provided by the GSM operator
GPRS Login
GPRS Password
Modem is always GPRS connected
Firewall disabled
Telnet is activated
Login for Telnet
Password for Telnet
Bitcoin system enabled
Bitcoin address associated with MTX

The system checks the account every 30 seconds
Wakeup input enabled
0 confirmations chosen as we want real time


  • The customer makes a Bitcoin transfer to the address associated with the MTX device. MTX does not use the wakeup input; instead, it checks every 30 seconds if a new Bitcoin transfer has been received (an unlimited tariff would be necessary in this case). Once a new deposit is detected, a URC message is send via the serial port (example: ^MTX_BITCOIN_INCOME_0.002)
  • The Bitcoin address must be unique for each MTX device. Therefore, if you have 10 MTX devices, you will need to generate 10 Bitcoin addresses. These are free and you can create as many as you like
  • Use of a QR code that contains the Bitcoin address is recommended for a more user-friendly experience. All Bitcoin wallets enabled for mobile phone use allow the Bitcoin addresses to be converted from QR codes by using the camera
  • If you wish, you can convert the Bitcoins into money (€, $, etc.) using any Exchange tools (BTC-E, Coinbase, Bitstamp, etc.)