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Arduino programming: Build a games console (part 1/2)

SCHOOL OF MAKING

Creating a set of rules for analogue control can

be complicated, but we’ve got an excellent

new function at our disposal

”

”

JOYSTICK CONTROL

We now want to write the code that reads the

joystick values and translates these into ship

movement. An analogue joystick is really just two

potentiometers, one each for the x and y axes,

with each sending a range of values from 0 to

1023. These values are delivered to the A0 and
      A1 analogue inputs in the Arduino. The joystick is
      spring-loaded to hold the middle position, where
      both x and y potentiometers read 511, and these
      values change as you move the stick. There are
      many ways these changes can be interpreted, and
      they’ll all result in slightly different gameplay. You
      could use the joystick as a digital input, for example,
      turning on positive x movement when the x value is
      greater than 511, but that loses the finer control you
      get from an analogue joystick.
      Creating a set of rules for analogue control can
      be complicated, but we’ve got an excellent new
      function at our disposal, and that is called map. The
      map function simply converts one range of numbers
      to another, such as from 10–20 to 1–10. It can
      also handle negative integers, and that makes it
      perfect for translating the raw values we get from
      the joystick’s analogue inputs into a value range
      that could represent the number of pixels we want
      our ship to move – in both positive and negative
      directions. This can even be accomplished with just
      a couple of lines:
      xValue = map(analogRead(JOYX), 0, 1024, 5, -8);
      yValue = map(analogRead(JOYY), 0, 1024, -5, 5);

Above

An analogue joystick

sends values between

0 and 1023 from (0,0) in

the top left to (1023,1023)

in the bottom right, with

(511,511) in the centre

Right

The analogue joystick

needs power and ground,

shared with the screen,

and two analogue inputs

for x and y and another

digital input for the switch

0,0

top left

0,511

left centre

511,0

top left

511,511

centre

511,1023

bottom centre

1023,511

right centre

1023,0

top right

1023,1023

bottom right

0,1023

bottom left