Real-Time I/O - BeagleBone - page 520

Solution

Recipe 2.3 shows how to read a pushbutton switch and Recipe 3.2 controls an external
LED. This recipe combines the two to read the switch and turn on the LED in response to
it. To make this recipe, you will need:

▪ Breadboard and jumper wires (see “Prototyping Equipment” )

▪ Pushbutton switch (see “Miscellaneous” )

▪ 220 Ω resistor (see “Resistors” )

▪ LED (see “Opto-Electronics” )

Wire up the pushbutton and LED as shown in Figure 8-1 .

Figure 8-1. Diagram for wiring a pushbutton and LED with the LED attached to P9_12

The code in Example 8-1 reads GPIO port P9_42 , which is attached to the pushbutton,
and turns on the LED attached to P9_12 when the button is pushed.

Example 8-1. Monitoring a pushbutton using a callback function (pushLED.js)
#!/usr/bin/env node
var b = require ( 'bonescript' );
var button = 'P9_42' ;
var LED = 'P9_14' ;

b . pinMode ( button , b . INPUT , 7 , 'pulldown' , 'fast' , doAttach );
function doAttach ( x ) {
if ( x . err ) {