Last Update: 03 Jun 2018
September 2004

ssd is a daemon for UNIX-based operation systems. It allows to shutdown the system using a calliper. This is useful for systems without a keyboard or similar. The daemon requires a small calliper, which can be built easily.

The calliper is connected to the RS232 interface of the system. After the daemon is running, a green LED shows the attendance of the daemon. If the calliper is pushed for longer than three seconds, the green LED turns off and a yellow one starts blinking. The blinking LED shows that the shutdown command is executed. The system is completely shutdown if both LEDs are off.

This projects bases on an idea by Guido Socher. He also developed the circuit.


In order to use the daemon a small calliper is required, which is to be connected to the COM-port of the system. It implements the depicted circuit and requires the listed parts.

  • 1 yellow low-power LED
  • 1 green low-power LED
  • 2 resistors 1.5 kΩ
  • 1 resistor 6.8 kΩ
  • 1 small calliper
  • 1 RS232 connector (female)
  • some wires