I was able to use the parallel port on my old 8 bit computer and set up a breadboard with 8 LEDs and by sending values 0 to 255 to the port, I was able to light the 8 LEDs in 256 different combinations. I then switched the 8 LEDs for optoisolators and built a crude board and was able to have a switch for 8 different items.

I would like to take this one step further and create a 8 bit to 256 bit multiplexer switch circuit.

I would ultimately like to use my old 8 bit computer to control Christmas lights around my house. I could do a lot with 256 switches (I guess it would essentially be 255 and 0 would be off).

The multiplexer switch is a bit beyond my abilities. I'm sure someone has already done this or something similar. Can someone point me in the right direction?

My career is in IT, but I was an electronics technician in the Air Force and I do have a fair bit of knowledge, but I am rusty and have never tried building my own 8 bit to 256 bit multiplexer switch circuit.

Thank you.

 

With 8-to-256 multiplexer, you can control only one LED at a time.

A better solution would be to use 8-bit serial shift registers. Then you can expand it to as many LEDs as desired.
For example, if you wanted to control 256 LEDs, you would need 32 shift registers.

The way this works, you shift serial data along a daisy chain. The shift clock can be very high, for example 10 MHz. It would take only 25.6 μs to shift data to 256 LEDs.

The other advantage is that you can easily have many fancy rotating patterns without requiring complex programming.

 

If you like controlling lots of little LEDs, learn about the individually addressable RGB[W] LEDs based on the WS2812 (or other) chips.

No longer any need for muxes.

 

Yes, WS2812B gives you full control of hundreds of LEDs with RGB and 256 levels of brightness, with very little code. If strips work for you, it is great, but you can also wire together individual ones for any configuration you want.