The Door Lock

2013-06-19: Door Relay was upgraded to a KMtronic Two Channel USB Relay Controller.

Relay interface uses a baud rate of 9600. Valid commands include (in hex, without spaces):

  • "FF 01 00": Turn relay 01 OFF
  • "FF 01 01": Turn relay 01 ON
  • "FF 01 03": Retrieve relay 01 state. Returns "FF 01 00" for off, "FF 01 01" for on.
  • "FF 02 XX": Same as above, but for relay 02.

Commands can be sent from the command line via echo -e "\xff\x01\x01" > /dev/ttyUSB0. The script merlo:/root/ retrieves and echoes the state of relay 01. Full documentation is available on the KMtronic site. See Manuals and Software Examples for more information. The manual for this relay controller and fully functional shell script examples are available at

The Depths of Time

Hi All,

The modem has now been replaced with the arduino and the small 5v relay 
board. It's working for now, but it's a hack and not even properly boxed 
up. [TPG] has already modified dispense to suit it. If it breaks, I'll let 
you keep the pieces.

For posterity, here are the super-sekret settings and commands: 

Serial over USB connected to merlo, 115200 8n1
Type "2;" and it will respond with "1,The UCC door is alive;"
Type "4;" and it will respond with "1,Opening door;" , keep the lock open 
for ten seconds and then say "1,Locking door;". The command codes are 
strange numbers because I hacked the CmdMessenger [1] library example to 
do the job.

I've found using picocom to check it is easier than minicom. The following 
command* will start picocom with the correct baud rate and a command 
character of x: `picocom /dev/ttyUSB0 -e x -b 115200'



Fixing the door lock

Symptom: Cries of "The door's broken." Door relay doesn't activate from snack machine, dispense or serial from Merlo.
Cause: The seeduino program seems to hang.
Fix: Restart seeduino (unplug/replug), then restart vendserver.

  • - [DTK]


text door relay diagram image

1. The power light should remain on at all time

1. The relay light should illuminate only when the door is unlocked, and otherwise be off.

The Wires Are Connected as Follows:

Lock - Con4 - Power

Relay(C) - Con3 - Lock

Power - Relay(NO)