How Do You Connect Resistors in a Keypad Interface?

[smuscat]

Hi guys

Can please someone submit a circuit diagram for the resistors connections to the keypad of the below tutorial?
http://www.winpicprog.co.uk/pic_tutorial9.htm
"As the switches are all interconnected, we need a way to differentiate between the different ones - the four resistors on the interface board pull lines COL1 to COL4 high, these four lines are the ones which are read in the program. So in the absence of any switch been pressed these lines will all read high. The four ROW connections are connected to output pins, and if these are set high the switches will effectively do nothing - connecting a high level to a high level, results in a high level."
Thanks!

 

[berkeman]

Hi guys

Can please someone submit a circuit diagram for the resistors connections to the keypad of the below tutorial?
http://www.winpicprog.co.uk/pic_tutorial9.htm
"As the switches are all interconnected, we need a way to differentiate between the different ones - the four resistors on the interface board pull lines COL1 to COL4 high, these four lines are the ones which are read in the program. So in the absence of any switch been pressed these lines will all read high. The four ROW connections are connected to output pins, and if these are set high the switches will effectively do nothing - connecting a high level to a high level, results in a high level."
Thanks!

They are just for resistors that pull the COL (column) lines high, probably to 5V or 3.3V, whatever the PIC power supply is.

 

[256bits]

http://www.8051projects.net/request.php?download.184"

See r2,r3,r4 connected to the 5v line.
Much more intuitive with a picture.

 

[256bits]

http://www.8051projects.net/download-d184-digital-code-lock-lcd-keypad-using-at89c2051.html

Maybe this link works

 

[alphy]

Hi there, thank you for your question. Based on the information provided, it sounds like the keypad interfacing schematic for the tutorial you linked is using a pull-up resistor configuration. This means that the four resistors on the interface board are connected to the four input lines (COL1 to COL4) and are pulling them to a high voltage (usually 5V). This is done to ensure that the input lines are not floating and to provide a defined voltage level when no switch is pressed.

The four ROW connections are connected to output pins, which means they are controlled by the microcontroller. When the microcontroller sets a ROW pin to a high voltage, it effectively disconnects that particular input line from the pull-up resistor, resulting in a high voltage reading on the input line. This is why, as mentioned in the tutorial, connecting a high level to a high level results in a high level.

I hope this helps clarify the circuit diagram for you. Let me know if you have any further questions. Good luck with your project!