Go Down

Topic: Shift register keypad (Read 1 time) previous topic - next topic


Nov 18, 2009, 07:03 pm Last Edit: Nov 18, 2009, 07:06 pm by pekkaa Reason: 1
In order to save precious input pins, I first tried to use an analog input to read keypad values. It didn't lead to good results, as I point out in this thread http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1256180034/12#12.

My next attempt was to use a shift register. The shift register I use is CD4021B.

I ripped the keypad from an old ericsson diavox phone  http://www.ericssonhistory.com/templates/Ericsson/Article.aspx?id=2095&ArticleID=1371&CatID=360&epslanguage=EN I found from the attic. In addition to row/column pins of the standard matrix keypads, it has two other pins. I don't know what the pin no. 9 is for, but the pin no. 8 is very useful. If I connect pin 8 to +5V, the corresponding row and column pins goes high when a key is pressed. There is no need to pull rows high/low one by one and scan the column pins as the standard approach goes. To be honest, I can't figure out how to read the keypad with a shift register without the extra pin. The shift register is parallel in, AFAIK it provides no means to put pins high/low that is needed in the standard approach. Please let me know if you know how it can be done with a shift register using the row/column pins only.

I made a little adapter board where the shift register sits on. The resistors are pull-downs for the shift register's input pins.

I removed the cable from the keypad and replaced it with a male header. It matches the adapter's female header. The wires from the adapter  goes to Arduino's three digital pins, +5V and GND.

I also wrote a modified version of Mark Stanley's and Alexander Brevig's Keypad library http://www.siterunner.fi/liitteet/outijapekka/materiaalipankki/8.zip. I has the same interface and event model as the Keypad library, only the constructor is different.

Go Up

Please enter a valid email to subscribe

Confirm your email address

We need to confirm your email address.
To complete the subscription, please click the link in the email we just sent you.

Thank you for subscribing!

via Egeo 16
Torino, 10131