Multiplexing

[Fear the Weasel]

Hi there,

I'm in the process of building a Midibox that uses encoders.  I plan on writing my own custom C code for the project so I've of course been going through all the current source code but there's one main feature of MIOS I don't understand.  Multiplexing.

Coming from a software background and not a hardware one I'm having a few problems understanding the concept of multiplexing LED's.  How does this work? (in a hardware sense)  Is the microcontroller going through each turning it on quickly then doing the same to the next set but so quickly I can't see the difference?

Just a brief explanation would be very helpful.  Sorry for my hardware newbieness and feel free to laugh out loud if my explanation is way off mark.....  ;)

Cheers.

[Screaming_Rabbit]

Is the microcontroller going through each turning it on quickly then doing the same to the next set but so quickly I can't see the difference?

... yes.

Greets, Roger

[Fear the Weasel]

Thanks!  That's sorta what I gathered from the source code but just wanted to make sure.    :)

[moogah]

What a multiplexer (mux) does can be described like this:

If you have 7 different signals that you need compress onto one wire you can set up a device to read the level of each input, one after another, and do this so quickly that you don't lose fidelity (think of it like sampling audio).  At the other end of the wire there is a de-multiplexer (demux) that switches in sync with the mux such that it reads the value of the signal at just the right time and routes it to an output so that what you see at a given output wire is what was seen at a given input wire. 

[Fear the Weasel]

Cheers!  I'm pretty new to electronics (come from a programming background) so all this extra info is gold to me.  ;D