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How to implement a keypad decoder

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saurav_sdpl

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In my design i am using 3x4 keypad, now with the same keys if i want to give an interrupt to the micro how can i implement this through hardware

For eg i want to generate an wake -up interrupt for the following key pressed
1*#,how can this logic be implemented through hardware
 

keypad decoder

Keypad requires periodic sequential scanning and if you want to put the scanning microcontroller to sleep something else has to scan it (keypad) instead ..

One option is to use dedicated keypad IC (with an interrupt) such as the MM74C922 ..
Here is it's detailed description:
https://www.elexp.com/tips/74C922.pdf

Regards,
IanP
 

what is a keypad decoder

I'm not sure what you mean by pressing the 1*# keys. Do you need a special sequence?

You can add a few "OR" diodes to you keyboard matrix, so when you press any key it sends an interrupt signal to the microcontroller. Here is an Atmel example:
"AVR240: 4x4 Keypad - Wake-up on Keypress"
http://www.atmel.com/dyn/resources/prod_documents/doc1232.pdf
 

4x4 keypad decoder

Simple solution is to wake up the CPU for short time every 1 or 2 seconds with timer interrupt
To scan the keys if any key pressed
And if not, to send the CPU to sleep
 

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