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Digital output extender module with multiplexer

A common problem, at least for me, when using I/O devices is running out of ports. When I was using the parallel I/O device in my rack box project, I ran out of outputs. I solved that by making this output extender. It’s quite simple; it uses a multiplexer circuit to multiplex (duh) 3 outputs and turn them into 7. It does have some limitations though…

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I/O module driven by a computer parallel port

With this unit a regular computer parallel (printer) port will give you 5 inputs and 8 outputs to use for something fun. And it’s very simply to build; one transistor and one resistor per output, and a single resistor for each inputs. The parallel port is pretty easy to access in most programming languages. The module as a 36 pin centronics connector, making it easy to connect to the computer using a regular printer cable.

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