http://www.info.kmtronic.com/software/Raspberry_PI/Raspberry_PI_KMTronic_USB_Relay.zip

USB One Relay commands:

 FF 01 00 - OFF command

FF 01 01 - ON command

                   FF 01 03 - Status request command

> FF 01 xx - Reply from relay

where xx is status: 01 - Relay is ON, 00 - Relay is OFF

Set baudrate to 9600b/s

Switch ON relay

Switch OFF relay

Status request