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Can anybody help me on this?

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I want to build a RF direction sensing robot ,So that it turns to the direction of the signal source. I have to fix a motor to do the turning but thats not the problem. The problem is that how do I make the circuit know which direction to turn?
Should I use teh Doppler shift method? And if I should how do i go about it.
Please help.
I would be extremely greatful to anybody who can help me.
Thank You very much
well, i dont think that the doppler effect could do, but also you must make that the source of your readio waves must be directional, like a light beam. you could use a IR beam or laser beam, or a flash light, but for the radio, it is more compliacated. basicly for all methods i talked about you can use 2 sensors at a certain distance on the robot wich will both receive the signal. so you make the robot turn so that the signal received by both of the sensors is the same strenght. for radio i think that is a bit complicated. so what you want to do is that you want your robot to follow the beam. and reorient it the way you change the direction of the radio waves. like i said, if you can create a directional radio source you can try to mount 2 antennas on it at a certain distance and compare the signals from the 2 antennas and reset the direction.
maybe some others have other ideas.

bogdanfirst is right, please re-consider the use of radio to do this. If you want it to be invisible, use infrared light or ultrasonics.

You can try to make two antennas as suggested and compare the signals, but this will be extremely inaccurate with commonly available materials. There are too many factors such as antenna construction, impedance mismatching, component tolerances, multipath, etc.. to make it possible for you to do.

You could try to measure the phase difference of the two signals, but you will some of the same problems as above. If you get a highly directional antenna and rotate it, this could be your best route. This would eliminate the tough comparing involved with two antennas, and it would give you a peak signal at a certain point. This would involve a bit of processing, but who said this was easy???


I am developing a robot that needs that property. It must reach the source so it needs to know where is it. Maybe is not your case but RF does not fit my project because you can get a maximum in the signal reception through a wall the same as through the air. Because of that I use ultrasonics which has some advantages:

It is very very easy to make the receiver directional (just cover it with a cylinder, like a traffic light).

It's over the problem of ignoring the obstacles because the obstacles reduce the power of the signal.

And ,too, it's over the problem of IR and laser, which need visual contact.

The point of RF where ultrasonics have nothing to do with is the reach of the signal.

Ultrasonics isn't soo peachy, but I admit that it is probably the best route in this case. The very nature of an ultrasonic system has many limitations. If the sound is absorbed, then you are left without any feedback. Also, you have a very sketchy picture of what is in front of you, whereas laser has extremely high point resolution.

I have seen some ultrasonic imagining, it is terrible. Nonetheless, it would be the best in this case. Laser would be cool, but it is far too expensive for many hobby applications.

Thank You All Very Much

I am extremely sorry for not acknowledging yout previous kind timely replies.
But I had queried manytimes like this in other forums and did not get any reply. I thought that it would be the same here. Now I know that this is the forum for me. Thank you All!!!

Now coming to the matter, I have decided on an idea, please advise me on this:

I wanted to make the pointer point to the direction of the transmitting source, so what i have :eek: decided to do is, make the motor rotate untill it recieves the highest signal strength. Obviously the highest signal strength will come from the actual direction of the source. So i connect a NOT gate to the output of the signal detector circuit so that the moment the detector circuit gats a "high" the motor goes "low" and stops. So suppose I move the transmitter a distance radially in a circle the motor starts turning since the detector becomes "low" and the motor becomes "high". This is only to find the direction of the transmitter when i turns around the reciever in 2 axes. Of course if the transmitter moves away from the reciever in the same axis the signal strength will become weak and the motor will start turning.

Now My problem is the detector circuit.
I need a circuit that will be able to detect the highest signal strength.
An FM reciever detector.
Please advise me on this.
Thank You Very Much
Yours Faithfully
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