Spency's digital-diy 18F PIC micro Tutorial

18F Keypad (4*4) Example

Swordfish has its own keypad library for 4 * 4 keypads, but I don't understand why it doesn't take a different approach to remove the need for external resistors as well to interface with the keypads...

Solution: Make my own Library! By only making a single pin and output, setting it high, and checking for a corresponding high input on the matrix, I can determine what button was pressed! You will still need a resistor network to tie the input pins to earth, but this a single component compared to 4 separate resistors.

I don't have a 16 Button keypad like the one above in my simulation software, but I do have the one shown below. The box looking thing at the top is a virtual terminal for USART data to be displayed with.

Circuit Diagram:

16 Button Keypad Entry

Note the PIC's power supply/oscillator are not shown

If your using PORTB for the keypad, then be sure to disable PORTB internal pull-ups if they are not already configured by default.

As each key does not represent its physical location (i.e. you press 1, it will return 5), the Key results must be formatted, I have done this by using a simple Select Case routine as shown below;

Device = 18F2520
Clock = 8
Config OSC = INTIO67

Dim Key As Byte

#option KEYPAD_PORT = PORTB
Include "INTOSC8.bas"           // sets up the internal oscillator for 8Mhz straight away
Include "usart.bas"             // to allow for USART data sending/receiving
Include "Keypad16.bas"          // for interfacing with 12 button keypads
Include "Convert.bas"           // to convert numbers into ascii strings


USART.SetBaudrate(br9600)

While True
    // wait for a key to be pressed, then convert it and send via uart
    Key = 0
    While Key = 0
        Key = Keypad16.Value
    Wend
    Select Key
        Case 1
            Key = "C"
        Case 2
            Key = "0"    
        Case 3
            Key = "="    
        Case 4
            Key = "+"    
        Case 5
            Key = "1"    
        Case 6
            Key = "2"    
        Case 7
            Key = "3"    
        Case 8
            Key = "-"    
        Case 9
            Key = "4"    
        Case 10
            Key = "5"    
        Case 11
            Key = "6"    
        Case 12
            Key = "*"    
        Case 13
            Key = "7"    
        Case 14
            Key = "8"    
        Case 15
            Key = "9"    
        Case 16
            Key = "/"    
    End Select
    USART.Write("Key Pressed: ", Key, 13)
    // wait for the user to release the key
    Keypad16.Debounce    
Wend

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