Keypads

Questions on other types of hardware and getting it talking to the ARM CPU
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YahooArchive
Posts: 1463
Joined: Fri Oct 19, 2012 5:11 am

Keypads

Post by YahooArchive » Thu Oct 25, 2012 10:10 pm

>Can you recommend to me a keypad (either 3x4 or 4x4 matrix) that
integrates well with this board? I'm building an alarm system for a
school project.

Here is a cheap keypad at SparkFun

http://www.sparkfun.com/commerce/produc ... ts_id=8653

Basically you tie the colums with pullup resistors and use the CPU
drive the rows low, one at a time. Note rows and columns are
interchangeable.
When you read the columns, the column corresponding to the switch
being pushed will short the row line to the column line. So you know
which button is being pushed.

So you will be using LOW (pin) for drive and INPUT(pin) to release it.

You will have to debounce inputs, which means, when keys are pressed,
the connection will be made but the switch may bounce for some time
normally 10s of milliseconds.



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