Sunday, November 6, 2011

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()

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

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Franck Mathieu said...

Hi Simon,

that's exactly what i am looking for my cats... does it work ?

can I have more info about your project ?




Asa M said...

Awesome project. It seems like there should be some way to set up an opamp or a 555 timer to do the same thing. A uC seems like a waste of computation power when all you need is a ping. I suppose I should back this comment with some circuitry, I'll have to look into it.
I also remember a couple of scratch built AM tx circuits in an old "Engineer's Notebook" from Radioshack. You're making me think......

Toby hijzen said...

Hi Simon,

Cool project! Did you finish this project? If so can you say a bit more about what the accuracy is and in what range it works. For example can I also use this to find my dog within my house if I combine it with a altitude sensor?

Kind regards,