user2964: I have this cheap RF link that I had working with the Arduni UNO, but I wanted to make it smaller and ATTiny85 should do the trick. The RF module is connected (data pin) to PB3 on the ATTiny. 
But I am having some problems. It does not work, and I don't know why. My code:
#include <SoftwareSerial.h>

// PINS
#define SERIAL_TX PB3

SoftwareSerial mySerial(-1, SERIAL_TX);

void setup() {
  pinMode(SERIAL_TX, OUTPUT);
  mySerial.begin( 1200 );
}

void loop() {

  mySerial.write(0xAA);
  mySerial.write(0xAA);
  mySerial.write(0xAA);

  delay(1000);
}


user630: The code you presented does not fit for working with the RF 433Mhz. I'm not sure what you think this code should do, but this is not the way to go with a 433Mhz transmitter.
I would suggest using a dedicated library for transmitting information using the 433. There are many libraries out there for doing that; two popular libraries would be the ManchesterRF and the VirtualWire, both includes code samples.
For example, sending data with ManchesterRF: 
#include "ManchesterRF.h" //https://github.com/cano64/ManchesterRF

#define TX_PIN 3 //any pin can transmit
#define LED_PIN 13

ManchesterRF rf(MAN_4800); //link speed, try also MAN_300, MAN_600, MAN_1200, MAN_2400, MAN_4800, MAN_9600, MAN_19200, MAN_38400

uint8_t data = 0;

void setup() {
  pinMode(LED_PIN, OUTPUT);  
  digitalWrite(LED_PIN, HIGH);
  rf.TXInit(TX_PIN);
}

void loop() {

  rf.transmitByte(++data, data*data);
  digitalWrite(LED_PIN, digitalRead(LED_PIN)); //blink the LED on receive
  delay(100);
}

In addition, there are many other blogs around going step-by-step how to use 433Mhz Tx/Rx with ATtiny85, google is your friend :)

2964: <p>I have <a href="http://www.dx.com/p/433mhz-wireless-transmitter-module-superregeneration-for-arduino-green-149254#.VJ2MwF4AQ" rel="nofollow">this cheap RF link</a> that I had working with the Arduni UNO, but I wanted to make it smaller and ATTiny85 should do the trick. The RF module is connected (data pin) to PB3 on the ATTiny. </p>

<p>But I am having some problems. It does not work, and I don't know why. My code:</p>

<pre><code>#include &lt;SoftwareSerial.h&gt;

// PINS
#define SERIAL_TX PB3

SoftwareSerial mySerial(-1, SERIAL_TX);

void setup() {
  pinMode(SERIAL_TX, OUTPUT);
  mySerial.begin( 1200 );
}

void loop() {

  mySerial.write(0xAA);
  mySerial.write(0xAA);
  mySerial.write(0xAA);

  delay(1000);
}
</code></pre>
 630: <p>The code you presented does not fit for working with the RF 433Mhz. I'm not sure what you think this code should do, but this is not the way to go with a 433Mhz transmitter.</p>

<p>I would suggest using a dedicated library for transmitting information using the 433. There are many libraries out there for doing that; two popular libraries would be the <a href="https://github.com/cano64/ManchesterRF" rel="nofollow">ManchesterRF</a> and the <a href="http://www.airspayce.com/mikem/arduino/VirtualWire/" rel="nofollow">VirtualWire</a>, both includes code samples.</p>

<p>For example, <a href="https://github.com/cano64/ManchesterRF/blob/master/examples/ManchesterTX_Byte/ManchesterTX_Byte.ino" rel="nofollow">sending data with ManchesterRF</a>: </p>

<pre><code>#include "ManchesterRF.h" //https://github.com/cano64/ManchesterRF

#define TX_PIN 3 //any pin can transmit
#define LED_PIN 13

ManchesterRF rf(MAN_4800); //link speed, try also MAN_300, MAN_600, MAN_1200, MAN_2400, MAN_4800, MAN_9600, MAN_19200, MAN_38400

uint8_t data = 0;

void setup() {
  pinMode(LED_PIN, OUTPUT);  
  digitalWrite(LED_PIN, HIGH);
  rf.TXInit(TX_PIN);
}

void loop() {

  rf.transmitByte(++data, data*data);
  digitalWrite(LED_PIN, digitalRead(LED_PIN)); //blink the LED on receive
  delay(100);
}
</code></pre>

<p>In addition, <a href="http://nerdralph.blogspot.co.il/2014/04/attiny85-as-433mhz-transmitter-fail.html" rel="nofollow">there</a> <a href="http://pidome.wordpress.com/manual-howtos/pidome-hardware/attiny85-433mhz-transmitter-with-i%C2%B2c/" rel="nofollow">are</a> <a href="http://labalec.fr/erwan/?p=1520" rel="nofollow">many</a> other blogs around going step-by-step how to use 433Mhz Tx/Rx with ATtiny85, google is your friend :)</p>
