Canine Radio Direction Finder - Part 1

After our new dog ran off when we were out, I decided it might be fun to make a radio direction finder, so that we can at least see in which direction he is.

So far, I have made the radio transmitter end of the project. In the second part of this blog I will look at the receiver and the directional antenna.

The transmitter is built using a low cost 433MHz AM Radio Frequency transmitter module. This is the module that I used RF SOLUTIONS - QAM-TX1 - MODULE TRANSMITTER AM 433MHZ but theses modules are pretty standard in their pinouts and features.

To provide pulses to the RF transmitter, I use an ATTiny45 programmed using an Arduino board as described here: http://hlt.media.mit.edu/?p=1229

The pulses are are a continuous series of 'Sputnik-style' beeps at a frequency of 300Hz.

The 3.7V battery and tiny slide switch were scavenged from a broken RC helicopter and the antanna is made by wrapping 17cm of solid core wire around a screwdriver.

To test out the transmitter, its corresponding 433MHz receiver module (RF SOLUTIONS - QAM-RX2 - MODULE RECEIVER AM 433MHZ) was fitted to some breadboard and an oscilloscope attached.

So there we go! We are receiving the signal. The next step is to build a directional antenna with ajustable gain, so that by sweeping it back and forth we can find the point of maximum signal strength.

The sketch:


int pin = 3;


void setup()
{
  pinMode(pin, OUTPUT); 
}


void loop()
{
  beep();
  delay(500); 
}


void beep()
{
  for (int i = 0; i < 100; i++)
  {
    digitalWrite(pin, HIGH);
    delayMicroseconds(200);
    digitalWrite(pin, LOW);
    delayMicroseconds(200);
  }
}

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