Most of engineering industry using PC to control hardware with using additional I/O card but with Lalim Parallel Port Control you can use your default printer port controlling external device such as switching on/off light or control electronic devices. What does this program [does is] trigger the parallel port (Printer port) 's data pin by your command. For example when you trigger pin2 , your printer port's pin2 becomes +5 volt . With this +5 volt , you can built your own electronic circuit to drive other external device. You can also built a simple circuit to test it by connect a LED with 1 kohm resistor direct to it pin.