How to send integers via popen? - cocoa

Question

I need to be able to send an integer from cocoa to an arduino.
It is easy to send characters, i.e. single digit integers, but I can't seem to find a way of sending two and three digit integers.
The purpose of this is to control the brightness of an LED continuously from 0 to 255.
So far, I can either turn it on and off using the following code:
int ledPin = 9; // LED connected to digital pin 9
int incomingByte = 0; // for incoming serial data
void setup() {
// initialize the digital pin as an output:
pinMode(ledPin, OUTPUT);
Serial.begin(9600);
}
void loop()
{
if (Serial.available() > 0) {
// read the incoming byte:
incomingByte = Serial.read();
if(incomingByte == 105){ //105 corresponds to i and is programmed in cocoa to turn the LED on
digitalWrite(ledPin, HIGH);
}
else if(incomingByte == 111){ //111 corresponds to o and is programmed in cocoa to turn the LED on
digitalWrite(ledPin, LOW);
}
}
}
However, I can't work out how to set values between 0 and 255. Instead of 'digitalWrite', I would use 'AnalogWrite', however, I don't know how to send the incomingByte to be a value between 0 and 255.
This is the cocoa code:
#import "MainController.h"
#implementation MainController
-(IBAction)ledOn:(id)sender{
popen("echo i > /dev/cu.usbmodem1411", "r");
}
-(IBAction)ledOff:(id)sender{
popen("echo o > /dev/cu.usbmodem1411", "r");
}
#end
Thanks.

Answer 1

You can treat the integers with more than one digits as cstring in your arduino code then convert them to integer via atoi().
The following code will capture the bytes from the serial buffer as cstring:
char buffer[MAX_BUFFER_SIZE]; // global c character array variable
boolean inputReady()
{
byte index = 0;
byte avail = Serial.available();
if(avail > 0)
{
while(index < avail)
{
byte val;
do
{
val = Serial.read();
}
while (val == -1); // if value is no longer -1, bytes are captured
buffer[index] = val;
index++;
}
buffer[index] = 0; //terminate the character array
return true;
}
return false;
}
Note: I prefer cstrings than the String class built in the arduino IDE since it uses more memory, but be careful using cstrings as they are prone to memory leaks if not managed well.
This is how your loop() block should look like:
void loop()
{
if(inputReady())
{
int pwmValue = atoi(buffer); // convert ascii buffer to integer.
if(pwmValue >= 0 && pwmValue <= 255) // filter values from 0-255
analogWrite(ledPin, pwmValue);
else
digitalWrite(ledPin, LOW); // turn off if pwmValue is more than 255
}
delay(100);
}
You can then send pwm values as string from your cocoa code via popen().
#import "MainController.h"
#implementation MainController
-(IBAction)ledPWMValue:(id)sender{
popen("echo 254 > /dev/cu.usbmodem1411", "r");
}
#end
I've tested this on my Arduino Uno and will probably work on other variants. I hope this helps you in your project and best of luck!