Joysticks rule

...especially when they're attached to a Nokia 6610 breakout board. This little fella provides 4-axis input (plus a "fire" button) using a single input pin. It's quite clever really, but simply uses a load of resistors, to change the input voltage depending upon which direction has been pressed.
Put the input from the miniature joystick on the Arduino Nokia board onto pin A0 of a PIC microcontroller and read the input values.



The Oshonsoft PIC18 the command for reading an analogue input is:

Adcin 0, joystickvalue

This takes the input from analogue channel zero (in our case, PORTA.0) and writes it to the variable "joystickvalue".
During testing, with an open connection (joystick centred, no movements made) the joystick value wavered between 169-170. At first this seems odd, but looking at the schematic datasheet we can see that the reference voltage from the joystick is between 0v and 3.3v.

Taking the average value of 170, and given that we're storing this data into a byte variable, we can see that (170/255)*5v = 3.3v.
So it all makes sense again - with no joystick movement, we expect to receive 3.3v from the joystick onto our analogue pin. And the value 170 does indeed represent a 3.3v signal when our PIC is powered by a 5v supply.

A simple routine was put together to write the value of the joystick input onto the Nokia screen. The following was determined:



This translates quite nicely into a simple subroutine for any project that uses this board. The routine waits for the joystick to be moved, stores the direction into a variable then waits for the joystick to be released again.
The routine can be called from anywhere in the program, though it might work quite nicely if called from a timer interrupt, since the user input is stored until the microcontroller is free to process it.

Dim joystickvalue as Byte
Dim jstick(5) as Byte
Dim buttonpressed As Byte

jstick(1) = 126 'right
jstick(2) = 88 'up
jstick(3) = 60 'down
jstick(4) = 26 'fire
jstick(5) = 4 'left

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getbuttonpress:
  'single input ADC for joystick press
  Adcin 0, joystickvalue

  'compare current joystick value to stored values
  'at rest returns 172-168, first value is 120-122 for "right"

  If joystickvalue < 140 Then
    For i = 0 To 4
      If joystickvalue < jstick(i) Then
        buttonpressed = i
      Endif
    Next i

    'debounce the button press
    WaitMs 1
    Adcin 0, joystickvalue
    If joystickvalue < 140 Then
      'wait for the button to be released
      While joystickvalue < 140
        'keep sampling the joystick to see whether it's been released
        Adcin 0, joystickvalue
      Wend
    Else
      buttonpressed = 0
    Endif

  Else
    buttonpressed = 0
  Endif

Return

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