Autonomous Homing Robot

Autonomous Homing Robot

tdoa botcut outsmall

This robot homes in on a selected radio transmitter by finding the direction of the signal.

tdoa pic

(Top pic) When robot is not aligned with transmitter, the red antenna gets the low part of the waveform and the blue gets the high part. This causes noise. (Bottom pic) When robot is aligned with transmitter, both antennas receive the same part of the waveform. Silence is the result.

Basically, if the signal hits one of the two antennas first, digital noise is created. If the signal hits both antennas at the same time (when the robot is facing the transmitter) there is silence.


A microcontroller interprets the noise to determine which direction the radio waves are coming from, then drives the robot towards them.

To learn more about how it works, see my Science Fair Project

Build this robot with step by step instructions!

The Radio Direction Finding (RDF) method I use in this project is also detailed here at Joe Leggio’s site.

3 thoughts on “Autonomous Homing Robot

  1. Thanks for your fantastic product and a informative reply on my query. my built is completed yesterday, with minor changes in codes, since i don’t have a full rotation servos, i have used L298 motor driver with 150 rpm motor, on connecting according to calibration procedure i got calibrated reading of 342.
    on running the robot, i am getting the reading in serial monitor as 190 in straight position.
    as per your code there is a big difference of reading between calibrated and actual.
    What could be the possible reason of such readings?

    Note: my 1/4 wavelength distance apart is 8 inch instead of 7.5 inch.

    I am using motorola T5720 walkie

  2. What is the purpose of the push buttons extension on the receiver? What spots on the circuit board should they be sodered to? If the receiver only receives then what is the purpose of having the push buttons? What happens if we don’t have the push buttons? When should a push button be pressed? How many points on the board should be sodered?

    1. I responded to your older comment for most of this on . They are just to access the receiver board as it’s inside the can. Where to solder depends on your walkie talke model, I just soldered to the circuit traces that go to the original buttons. The button extension is literally just there to use the board with it in the can, so you can change channels and such. See my reply to your other comment. Good luck on your project!

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