Switch Multiplexing

williB said:

Yeah ,but say you wanted to add 9 switches to your project and you only had one input and one optput left..
a single 4017 seems like a viable solution
* ducks and covers *
:lol:

Click to expand...

Yes, it's a viable solution, as I mentioned before, it's commonly used.

EDIT : Nigel can your matrix detect two switches being pressed at the same time ??

Click to expand...

Yes, it only depends on the scanning software you write - the keyboard you're typing on now almost certainly uses software scanning of a keypad matrix (just bigger!), as do your remote controls, mobile phone, microwave oven - almost anything with any number of keys.

See how my post made you all think outside of the box... :wink:

Configure this pin as an a to d and bias it to ground with 10k. Let each switch pull the pin high through a different resistence. Now read the atd in
and use software to figure out what switch is pushed.

ex sw 1 = 1k voltage = 4.5 volts
sw 2 = 10k voltage = 2.5 volts
sw3 = 20k voltage = 1.5 volts
no switch voltage = 0 volts

why not simply stick in one more pic or bigger pic?
using additional pic with only 1 or 2 io pins for communication
and all other pins for multiplexing you can add
significant number of switches.

there is one problem with the open loop counting method
like in 4017 example: it works as long as you don't loose count.
i would feel better if i could reset it when ever i want to but this means
one more pin.

maybe you don't need any other chips at all... how are you using existing ones (other than two you already mentioned)?