4x4 Switch Matrix Problems

[pmn2002]

Does anybody have aquick and easy solution for decoding a 4 row 4 column switch matrix.I've tried using logic etc but i can't find anything simple.I need a circuit that will indicate via led's which switch is being pressed.

Any ideas??

 

[aglet1000]

4x4 switch matrix discussion

I dont have a circuit for you but I will discuss the problem.
You need a 4x4 switch matrix. right...

Vcc---|-------|-------|-------|------A0
| SW0 | SW1 | SW2 | SW3
Vcc---|-------|-------|-------|------A1
| SW4 | SW5 | SW6 | SW7
Vcc---|-------|-------|-------|------A2
| SW8 | SW9 | SWA | SWB
Vcc---|-------|-------|-------|------A3
| SWC | SWD | SWE | SWF
| | | |
| | | |
| | | |------B0
| | |------------B1
| |------------------B2
|------------------------B3

This keypad would work like this. We will cycle B0-B3 one line low at a time.
ie 1110
1101
1011
0111
As we do this we will check the A0-A3 lines if anyone of these goes low then we have a key pressed.

B0-B3 A0-A3 Switch
1110 1110 SW3
1101 SW7
1011 SWB
0111 SWF
1101 1110 SW2
1101 SW6
1011 SWA
0111 SWE
1011 1110 SW1
1101 SW5
1011 SW9
0111 SWD
0111 1110 SW0
1101 SW4
1011 SW8
0111 SWC

If none of the signals is low then no key is pressed. The simplest way to do this is with a micro processor since it can be programmed to do all of the decoding.

If this is not an option maybe a counter on the B0-B3 signals and a Decoder on the A0-A3. When the counter switches the decoder checks the inputs.

This is not 100% complete dicussion but should give you something
to start with.

I made this beautiful diagram and nothing....

 

[gabby]

Hi
If you want easy complete solution you can use
74c922 or 74c923 (keyboard controller)

Or make it in a small uc or cpld and (prog debounce filter for it).

Best regards.

 

[srhoar]

nxn decoder

Just use an EPROM and 4-16 decoder.
BTW a micro would be easier.

 

[pmn2002]

thanks for the help i'm going to use a micro and a seven segment display