Hello 
I have a project with two arduino cards witch need to communicate a int (0 to 128) between them.
I tried different ways to make this working and it steel not working 
(433mhz, 2.4ghz) and now I am trying to transfer an int by optical fiber. But, I would like to send and receive the data by digital (0,1) and not by analog.
So : - The arduino receives an int by serial port, then it converts this int to a binary array and send this binary array to the led → 1st arduino
- The arduino receives the the light by a photoresistor (connected to analog port of the arduino) and when the value is over “x” > the bit is 1 else the bit is 0
I searched on the internet and I found this :
const byte numPins = 7;
byte pins[] = {13, 14, 15, 16, 17, 18, 19};
void setup() {
Serial.begin(115200);
}
void loop() {
while(!Serial.available()); // Do nothing until serial input is received
byte num = Serial.read(); // Get num from somewhere
for (byte i=0; i<numPins; i++) {
byte state = bitRead(num, i);
digitalWrite(pins[i], state);
Serial.print(state);
}
Serial.println();
}
Original post here : https://forum.arduino.cc/index.php?topic=119261.0
I think it will work for me, I edited this a bit :
const byte numPins = 7;
const int ledPin = 6;
void setup()
{
// put your setup code here, to run once:
Serial.begin(9600);
}
void loop()
{
// put your main code here, to run repeatedly:
while(!Serial.available()); // Do nothing until serial input is received
byte num = Serial.read(); // Get num from somewhere
for (byte i=0; i<numPins; i++)
{
byte state = bitRead(num, i);
//digitalWrite(pins[i], state);
delay(10);
if(state == 1)
{
digitalWrite(ledPin,HIGH);
}
else
{
digitalWrite(ledPin,LOW);
}
//Serial.print(state);
}
}
And I have a problem with the receiver, because I dont know how to convert the binarry array to a int.
Here is my RX code :
int sensorPin = 3; //Sensor witch will receive the data from the led
int limit = 1023/2; //Var witch will define when the signal is "1" or "0"
int received; //Var witch will stock the value from the analog pin
const byte numPins = 7; //How many bits ? (2^numPins)
int bits[7];
void setup() {
// put your setup code here, to run once:
Serial.begin(9600);
}
void loop() {
// put your main code here, to run repeatedly:
while(analogRead(sensorPin) < limit){} //while sensor pin < limit, do nothing
received = analogRead(sensorPin); //Those whiles sync the data receiving
while(analogRead(sensorPin) > limit){} //while sensor pin < limit, do nothing
for(byte i=0; i<numPins; i++)
{
received = analogRead(sensorPin);
if(received < limit)
{
bits[i] = 0;
}
else
{
bits[i] = 1;
}
}
}
Thanks for your help
, I also would like to improve the fiability of the data that travel in the optical fiber (no errors :p), a checksum will double the price (2*100m optical fiber = 60€ ; and the code will get a bit hard for me), but it still a good idea 
)