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Electronics Projects: How to Build a Parallel-Port LED Flasher

This electronics project presents a simple breadboard circuit that connects eight LEDs to the eight output pins of a parallel port. To complete this project, you need to have a computer with a parallel port, and you need to install the Kit 74 parallel-port software.

To connect the Kit 74 board to a computer, you need a printer cable with a DB25 male connector on one end and a DB25 female connector on the other end.


After you assemble the Parallel Port LED Flasher, you can test it by connecting it to your computer’s parallel port, opening a command prompt, and using the RELAY command to send data to the port. To turn on all eight LEDs, for example, run this command:


You may need to run the command twice to make the LEDs turn out. This requirement is due to a flaw in the RELAY command itself, not to a problem with your circuit or your computer’s parallel port.

Once you have completed this project, the finished parallel-port LED flasher circuit is connected to the male DB-25 connector on one end of a parallel printer cable. The other end of this cable is connected to the computer.

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