433MHz transmitter and receiver pair doesnt work I have a pair of 433 MHz transmitter and receiver:



Transmitter is connected to Arduino pro mini, receiver to Arduino Uno R3. 

Output of receiver on serial looks like that (it doesn't change much):

Basicly I am getting either 75x or zero regardless of transmitter is on or off.

in &gt; upper
756
in &gt; upper
758
0
0
 0
in &gt; upper
758
0
in &gt; upper
757
in &gt; upper


Transmitter code:



#define rfTransmitPin 4  
#define ledPin 6

void setup()
{
    pinMode(rfTransmitPin, OUTPUT);     
    pinMode(ledPin, OUTPUT);    
}

void loop()
{
    for(;;)
    {
         digitalWrite(rfTransmitPin, HIGH);     //Transmit a HIGH signal
         analogWrite(ledPin, 255);              //Turn the LED on
         delay(500);                            //Wait for 1 second

         digitalWrite(rfTransmitPin,LOW);       //Transmit a LOW signal
         analogWrite(ledPin, 0);                //Turn the LED off
         delay(500);                            //Variable delay
    }
}


Receiver code:

const unsigned int upperThreshold = 70;  //upper threshold value
const unsigned int lowerThreshold = 0;  //lower threshold value
const int ledPin = 13;

#define ReceiverPin  A0

void setup() 
{
    Serial.begin(19200);

    pinMode(ledPin, OUTPUT);

    DiodeTest();
}



void loop() 
{
   int data = analogRead(ReceiverPin);
   delay(50);

   if(data&gt;upperThreshold)
   {
       digitalWrite(ledPin, LOW);   //If a LOW signal is received, turn LED OFF
       Serial.println("in &gt; upper");
   }

   if(data&lt;lowerThreshold)
   {
       digitalWrite(ledPin, HIGH);   //If a HIGH signal is received, turn LED ON
       Serial.println("in &lt; lower" );
   }

   Serial.println(data);
}
These types of receivers are AC coupled so you will not be able to do what you are doing as you need to have regular transitions in the signal and not stay in one state for too long.

They are also limited in the speed at which they will work, I expect 19200 bps is too fast.

You need to use a modulation technique such as Manchester Encoding or other technique that guarantees a suitable density of transitions, can synchronize the data and perform error checking.

One popular software library that does this is VirtualWire Arduino Library that is designed for Arduino and the type of transmitters and receivers you are using.