Charlieplexing Inputs?

Forum 2005-2010 (read only) Hardware Interfacing
1

Im planning on building a tic tac toe game with 9 leds and 9 pushbuttons

I got the LEDs figured out but I run out of pins when it comes to the inputs, so my question is, is it possible to somehow charlieplex inputs? If so how does one do it? after some research on google I, it seems that I need some diodes but that's about all I understand. Example schematics and code on how to read the inputs would be appreciated.

2

Unless you have a lot more going on, you should have plenty of I/O with simple matrix multiplexing. You'll only need 6 pins for output and 6 for input (3 rows x 3 cols). You could also combine the row drivers between the LEDs and buttons to get down to 9 total I/O pins.

3

please explain the 3x3 button matrix...
how would i connect this to the arduino and how do i read the inputs.
Like I said, Iv already know how to make the 3x3 led matrix with 6 arduino pins, I just need help with the buttons

4

Here you go:

Take each row low in turn, and for each row read each of the columns.

5

A month or two ago, there was a posting here from someone who had come across a really clever way to connect a small matrix of buttons to a network of resistors so that each button wound up producing a unique resistance. By tying one end to ground, and the other to another resistor to Vcc, it formed a voltage divider that allowed the button to be detected by a single analog input.

I'm pretty sure it was done with about 10 or 12 buttons, so it could work for your application.

It's worth trying to find it. Try forum searches with terms like "switch" or "button" and "single input" to track it down.

Ran

6

Concerning the circuit above, you need a diode in line with each switch to avoid phantom detection when more than one switch is pressed at once.
Have a look at the switch input part of my 8 by 8 monome:- Econo Monome

7

Thanks for the help everyone. I think i will try the resistor/analog method that Ran suggested. It sounds pretty easy and only uses one pin. If that dosent work for some reason, I will try the schematic ajb posted. Once again I thank everyone for their time and help.