a few days ago i purchased a keypad.

1 2 3
4 5 6
7 8 9
* 0 #


okey i have four line 7 line to operate with this keypad.

row1 row2 row3 row4 col1 col2 col3.


if i connect row1 to +5 and connect the col1 to LED and ground then pressing only 1 button will cause the LED to lit. so key 2 will lit the LED with LED is connected to col2 and so on. problem is when i tested this way with 8051 then it detect the presence of keypress evey time it try to detect the keypress. i suspect its because when no key is pressed then some noice is coming in. so i need some pullup configuration so that by default the col's lines connected to 8051 has a default value like logic 1 and when key is pressed then its corresponsing col line becomes logic 0 so two default values whcih are sure as i am not sure what is appearing when no key is pressed on col lines. but i have 7 line 4 for rows and 3 for cols coming in and out of the keypad. can some body help me how the col lines be connected with resistances and +5 and to the input of the 8051 i mean some pull up configuration arrangement.




Shahzad