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extending keypad by using just 8 wire

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INGLE.SHUBHAM

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Hello,
im designing a keypad i tried with 4*4,
but the total combination of the above condition is.
for 4*4 the total and max combination is 16.
Keypad-4x4-Matrix-Keypad-structure.jpg


and i want the total of 20 combinations so which technique i can use.
if you have only 8 wire



please suggest me something
 

Hi,

Use 3 wires for colums and a 3 to 8 demux ( like HC138). This gives 8 columns.
Now if you combine them with 5 rows you are able to decode 40 keys.

Klaus
 

INGLE.SHUBHAM said:
please suggest me something
Click to expand...

If you have 8 wires (signal wires) you can handle 2^8 combinations.

If you consider one wire must be a ground one (return path for the signals) then you will have 2^7 combinations.

If you need also power to be delivered by these 8 wires, then you lose one more wire, and will have 2^6 combinations.

Your old keyboard with 101 (ore more) keys works on four or five wires. The key presses are sent out as serial codes.

The scheme you have shown is the matrix is suboptimal- you need coders and decoders to reduce the number of wires. 4 row wires can be encoded by 2 wires. Similarly 4 column wires can be encoded by 2 wires. That makes a total of 4 wires.
 

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