KMTronic USB Relay controller One Channel Box allows a PC to control a single external device using simple RS232 commands – is fully powered from the USB bus
For 12V/24V DC 15A or 120V/220V AC at 10A max.
usbrelay.exe -c:<COM port> -r:<RELAY>#<STATE> -b:<BROADCAST> -q
usbrelay.exe -c:5 -r:1#1 (this will turn on relay)
usbrelay.exe -c:5 -r:1#0 (this will turn off relay)