(G) On Keypad & Sensor :
1. How many I/O interface pins between keypad (4x4) and PIC18f4520?
- Keypad (4x4) has 8 I/O interface pins.
- In this example schematic that has RB0 to R07 connected to the 8 I/O pins on to the Keypad (4x4)

- PIC18f4520 has 36 I/O pins that grouped into 5 ports
- It should require 8 pins to connect a 4x4 keypad.

2. How to detect if a key is depressed?
E.g. Of flowchart when things are input.
E.g. Of flowchart when things are input.
End

End

Wait for Key Release
Wait for Key Release
Swap I/O back to original setup
Swap I/O back to original setup
Combine ‘R’ and ‘T’ and put into global variable
Combine ‘R’ and ‘T’ and put into global variable
Read another input (Keypad) and put into variable (e.g. ‘T’)
Read another input (Keypad) and put into variable (e.g. ‘T’)
Swap I/O
Swap I/O
Read the input (from Keypad) and put into variable (e.g. ‘P’)
Read the input (from Keypad) and put into variable (e.g. ‘P’)
Start
Start
- When a key depression has been detected and an interrupt generated, the MCU will need to determine which of the keys is being pressed.
- E.g. Initial a row high, and scan the 4 columns to see if any are high, if one is, then you have found a pressed key.

3. How to identify which of the 16 keys were depressed
(decode the key from the (4x4) matrix)?

-The Keys are in a matrix, the PIC must determine which row and column matches the key press.
- Once a key is pressed, a row/column circuit will be closed and the row (input) will pull low due to the column (output) being driven low.
- E.g. Like the input of number of “pull-up” is record into keypad is now put into variable ‘P’ and another input like time “min” is set, which is now put into variable ‘T’.
After that both is stored, will wait for the Key to Release.
- Determine Rows and Column, for the pins and