How to code in C for Alphanumeric 4x3 keypad

Question

Currently I am working on a project which has following setup.

AVR micro-controller
IDE - AVR Studio
Operating system - FreeRTOS

For input I am using a keypad matrix of 4x3. I have already coded for 4x3 keypad to take inputs as numbers. But now I want to make it alpha-numeric. Like we see in our mobile phone keypads.

Example - Key 2 will be used to take input for 2,a,b,c. Single press key 2, we will get number 2, double press key 2 then we will get 'a', tripple press key 2 then we will get 'b' and fourtimes press key 2 then we will get 'd' on scree.

I hope all of you understood what I mean above. Can anybody give some code idea in C to implement this type of functionality?

Do you have any method for providing the user with feedback on what he has chosen to input? — blueberryfields, Sep 04 '11 at 05:13
i want to implement this and i want to ask if you could do this. could you tell me how? — Sepehr Hamzehlooy, Oct 16 '16 at 09:18

score 2 · Answer 1 · answered Nov 23 '12 at 08:41

see the issue is when you press 2(say) in xxx sec time later after 30 millisec if you check and find that 2 is pressed then there are two cases. case1> the pressed key is new and is same as previous case2> the pressed key is same as previous and it is pressed from xxx till now contineously.

score 2 · Accepted Answer · answered Sep 04 '11 at 05:15

You most likely just need to keep track of the system time of the last key press and compare it to the system time of the next key press. If the current key is the same key as the last press and the time between presses is small (say, under one second), replace the current input character with the next character in the list of characters for that key. If the time difference is more than one second, or if a different key was pressed, accept the current character and add a new character, starting at the first character in the list for the key.

How to code in C for Alphanumeric 4x3 keypad

2 Answers2