Double click on the file blinkled.js within the demo directory and you’ll see the code from Example 7-1 appear in the editor pane. If you’d like to see an external LED blink, wire up an LED to pin 14 on header P9 (similar to what you did in Connect an LED but to pin 14 on P9 instead of pin 12 on P8). The code will toggle that pin and it will also toggle the on-board LED labeled USR3, which is right next to the Ethernet port (so if you don’t wire up the LED, you can still see the onboard LED blink).

var b = require('bonescript'); 

var leds = ["USR0", "USR1", "USR2", "USR3", "P9_14"]; 

for(var i in leds) {
    b.pinMode(leds[i], b.OUTPUT); 
}

var state = b.LOW; 
for(var i in leds) {
    b.digitalWrite(leds[i], state); 
}

setInterval(toggle, 1000); 

function toggle() { 
    if(state == b.LOW) state = b.HIGH; 
    else state = b.LOW; 
    for(var i in leds) { 
        b.digitalWrite(leds[i], state);
    }
}

Hover the mouse over the tiny bug icon to the left of the word Runner, in the lower-right corner of the window. If the icon is green and if the hover text says “Run in Debug Mode” (Figure 7-2), click the icon to turn off running in debug mode. This will ensure that when you run something in Cloud9 that it won’t immediately pause in the debugger and that any output text will be displayed at the bottom of Cloud9 every time you click Run.

Figure 7-2. Turning off debug mode in Cloud9

When you click the Run button, you’ll see all four USR LEDs blinking on the board and if you hooked up an LED to pin 14 on header P9, you should also see that flash in sync with the on-board LEDs. Press “Stop” to end the process.

What’s interesting about Example 7-1 is that it creates a new function called toggle and then uses setInterval to execute it once every second. Using this method, you can set up multiple functions to run independently and concurrently, but able to access the same variables and data if you wish.

To learn about reading a digital input with BoneScript, create a new file called inputPrint.js with the contents of Example 7-2. In Cloud9, it’s as easy as clicking the File menu and selecting New File. When you’re done inputting the code, save it (File→Save) and you will be prompted for a name (inputprint.js) and location.

Just like you did in Input, wire up a button or switch to pin 11 on header P8.

var b = require('bonescript');

var inputPin = "P8_11"; 

b.pinMode(inputPin, b.INPUT); 
b.digitalRead(inputPin, printStatus); 

function printStatus(x) { 
    if (x.value == b.HIGH) { 
        console.log("The pin is HIGH");
    }
    else { 
        console.log("The pin is LOW");
    }
}

When you run the script, the code will be executed once and will display the state of the button or switch in the Output tab at the bottom of Cloud9. Try changing the state of the button or switch and running the script again. If you’re using a momentary switch, be sure to hold the button down (or keep it released) while you run it.

Example 7-2 also demonstrates the callback functionality of the BoneScript library. The digitalRead function can take two parameters (or inputs):

digitalRead(pin, callback)

The function printStatus created in Example 7-2 will accept a single parameter, or input, designated by the x in parentheses next to the function’s name. Within the function, that input will be referred to as x. When digitalRead executes printStatus, it will pass x.value or x.error so that printStatus can take action based on the state of the pin (or any errors that may have occurred).

var b = require('bonescript');

var ledPin = "USR3";
var inputPin = "P8_11";

b.pinMode(ledPin, b.OUTPUT);
b.pinMode(inputPin, b.INPUT);

b.attachInterrupt(inputPin, true, b.CHANGE, printStatus); 

var state = b.LOW;
b.digitalWrite(ledPin, state);

setInterval(toggle, 1000);

function toggle() {
    if(state == b.LOW) state = b.HIGH;
    else state = b.LOW;
    b.digitalWrite(ledPin, state);
}

function printStatus(x) {
    if (x.value == b.HIGH) {
        console.log("The pin is HIGH");
    }
    else {
        console.log("The pin is LOW");
    }
}

If you connect a potentiometer or other analog sensor to the analog input pin 32 on header P9 as instructed in Connecting a Potentiometer, you can also get readings from it in BoneScript. Example 7-4 shows how to take analog readings from sensors and write their values to the console.

#!/usr/bin/node

var b = require('bonescript');

var inputPin = "P9_32";

loop(); 

function loop() { 
    b.analogRead(inputPin, printValue); 
    setTimeout(loop, 1000); 
}

function printValue(x) { 
    console.log(x.value); 
}

This example also demonstrates another way to set up a loop that executes repeatedly, but the effect is slightly different than in Example 7-1. The loop function in Example 7-4 includes the code to schedule itself to run again one second after the code before it has been executed, rather than just executing the loop once per second (no matter how long it takes to execute the code in the loop).

It would be a good idea to use the looping method in Example 7-4 if you think the code in the loop function may take longer than the interval to execute.

The analogWrite function can take two parameters:

analogWrite(pin, callback)

As discussed in Analog Output (PWM), only certain pins can be used for analogWrite functions. Be sure to review Table 5-1 when choosing what pins to use for PWM. Example 7-5 uses pin 13 on header P8.

var b = require('bonescript');

var ledPin = "P8_13";

b.pinMode(ledPin, b.OUTPUT);

b.analogWrite(ledPin, 0.05); 

The analogWrite function can take four parameters:

analogWrite(pin, value, frequency, callback)

var b = require('bonescript');

var ledPin = "P8_13";
var fadingUp = true; 
var level = 0.0; 

b.pinMode(ledPin, b.OUTPUT);

b.analogWrite(ledPin, level);

changeLevel(); 

function changeLevel() { 
    if (level > 1.0) {
        fadingUp = false; 
    }
    if (level < 0) {
        fadingUp = true; 
    }

    if (fadingUp) {
        level = level + 0.01; 
    }
    else {
        level = level - 0.01; 
    }
    b.analogWrite(ledPin, level); 

    setTimeout(changeLevel, 10); 
}

If you’d like to execute a script by simply typing its name, put the following on the first line of your script. This will instruct the system to look for the Node interpreter when executing the file.

#!/usr/bin/node

You can then set the file as executable:

root@beaglebone:~# chmod +x myScript.js

When you’re in the directory with the file, you can now execute the file just by typing its name after ./:

root@beaglebone:~# ./myScript.js

If you’d like to be able to execute the file no matter what directory you’re in, see Executable Scripts.