How Keypad Circuits Works

UNDERSTANDING KEYPADS CIRCUIT, A WAY TO LEARN HOW TO REPAIR KEYPAD PROBLEM

Understanding the Keypad circuit may help and boost your knowledge on fixing keypad problem issues on mobile phones. Keypads is a part of user interface being used to navigate or enter numbers, letters and characters, browse application, sends information and etc.

 How keypad circuits works and which components or parts did this circuit is being connected.

The each and every key switching pads is being divided and grouped into rows and columns. Each rows and columns were group into 2 -5 keypads switch. This rows and columns have each corresponding lines according to each and every group of switching pads.

This lines of rows and columns is being filtered for EMI and ESD protection the EMI filter is made of tiny chip that used to protect such EMI and ESD interference.

This rows and columns lines are digital switching signals generated by the application processor to trigger or activate every corresponding digital datas that is being stored and programmed within the mobile phone system memory. This diagram below is an Application Processor that generates and feeds then receives digital data switching signals.

This digital data frequency signals corresponds and interpreted to each key characters that are marked on each keypads. Like for example a combination of row 2 and column 3 will triggered the number 3 when hitting on it.

how the switching signal is being triggered to process a command data.

Various mobile phones have different keypads layouts and specification. A joystick and a volume switch is also parts of keypads switching circuits. Some keypads module designs are made into a flexible wirelike those Slide Type package of mobile phones. Some flexible wires are very vulnerable and common cause of keypad malfunction.

A keypad Matrix (that is i suppose a HEX matrix, with 16 pushbuttons) works a little like a transistor memory exept for it uses fisical switches istead of transistors:

It has 4 input lines, imagine four wires running vertically, and four output lines running across the first. If some of the crossings is pressed, it's wires are shortcut. e.g.:

Call the horizontal wires A0 to A3 and the vertical wires B0 to B3

the matrix of connections is like this:

A0B0 A0B1 A0B2 A0B3

A1B0 A1B1 A1B2 A1B3

A2B0 A2B1 A2B2 A2B3

A3B0 A3B1 A3B2 A3B3

then you cycle the input lines high (use a counter for example) and for each input line you read the output lines. The point where high lines cross indicates a pushed button. If you pull B1 High (and the others low) if some key is pressed the voltage is transferred to the corresponding row wire, so if you get A1 and A3 high as output you know that the buttons (A1B1) and (A3B1) are pressed.