Low frequency radio transmitter

Hello,

I am working on a project for an embedded systems class that will be using rf signals to help triangulate an autonomous car in a 6ft X 6ft area. I am aware of some of the different rf modules that allow the arduino to send data at 433MHz. However, I don't need to send specific data, I just need to output a constant radio frequency that another arduino could listen for.

If I wanted to create a 300 Hz signal, could I attach a wire to one of the arduino pins and constantly pulse that pin 300 times a second? Would I need any amplification to be able to see this signal on another arduino?

I am new to rf and do not have much experience with it but thought this would be a fun project to work on. Any help is greatly appreciated!

thanks!

cstang:
Hello,

I am working on a project for an embedded systems class that will be using rf signals to help triangulate an autonomous car in a 6ft X 6ft area. I am aware of some of the different rf modules that allow the arduino to send data at 433MHz. However, I don’t need to send specific data, I just need to output a constant radio frequency that another arduino could listen for.

If I wanted to create a 300 Hz signal, could I attach a wire to one of the arduino pins and constantly pulse that pin 300 times a second? Would I need any amplification to be able to see this signal on another arduino?

I am new to rf and do not have much experience with it but thought this would be a fun project to work on. Any help is greatly appreciated!

thanks!

Hi,
Welcome to the forum.
The problem will be the size of the aerials and ablility of them to be directional.
300Hz would require a very large aerial for the transmitter, and the receiver aerial likewise, especially if you want them to be directional.
An ideal aerial 1/4 wavelength at 300Hz = 250,000 meters long.
Even loading a shorter aerial would be not be practical for your application.
Tom… :slight_smile:

cstang:
Hello,

I am working on a project for an embedded systems class that will be using rf signals to help triangulate an autonomous car in a 6ft X 6ft area. I am aware of some of the different rf modules that allow the arduino to send data at 433MHz. However, I don't need to send specific data, I just need to output a constant radio frequency that another arduino could listen for.

If I wanted to create a 300 Hz signal, could I attach a wire to one of the arduino pins and constantly pulse that pin 300 times a second? Would I need any amplification to be able to see this signal on another arduino?

I am new to rf and do not have much experience with it but thought this would be a fun project to work on. Any help is greatly appreciated!

thanks!

You could create it that way. A square wave with perfectly sharp corners contains an infinite number of frequencies. However, the other Arduino cannot receive RF and you know that. You need a "receiver" for 300 Hz to convert the RF back to DC and then ensure it is between 0 and 5 volts.

Paul

Low frequency radio is totally unsuitable for navigation in a 6ft x 6ft area. It can be used on a GLOBAL scale.

The wavelength of a radio system needed for successful navigation needs to be much shorter than the distances involved.

I think the frequency you mentioned is out by a factor of 106 at least.

Even if you chose a more suitable frequency, I think that you would be plagued with problems caused by multiple reflections from surrounding objects.

This would be SLF or ULF even.

For triangulation, the best resolution on distance you can get is a single wavelength, so that would give you a 1,000 km resolution. Also the higher the frequency, the more directional your antenna gets.

If you're looking for a specific signal, you could modulate the signal: create a 433 MHz beacon, and then switch that on and off at your 300 Hz frequency. That would be similar to how modulated IR works, albeit at lower frequencies.

cstang:
Hello,

I am working on a project for an embedded systems class that will be using rf signals to help triangulate an autonomous car in a 6ft X 6ft area.

Put 3 lights spaced around the area. Have a rotating "scanner" (i.e. a shielded photodiode or LDR) that produces a pulse when it sees a light. Record the angles at which the 3 lights are detected, Calculate the position.

Mariners used this for hundreds of years.

...R

Thank you for all of the suggestions!

So if I am trying to use rf signals to triangulate a small toy cars position in a 6ft X 6ft area, I would need much higher frequencies than 300 Hz since the antenna needed to receive this signal would be massive. Is this true even in such close range?

If I were using 3 beacons around this 6 X 6 area, is it possible to judge location by signal strength from the beacons? I would think I would need 3 beacons transmitting diffferent frequencies and 3 seperate antennas on the toy car to determine which signal is stronger. Is this a possibility? Are there more feasible options?

I like the idea of using photodiode or LDRs, but for this project I would like to do what I can with radio signals.

The cheapest radio locator option I know of is Pozyx. Around US$ 500.

Google "indoor localization" for discussions.

cstang:
If I were using 3 beacons around this 6 X 6 area, is it possible to judge location by signal strength from the beacons?

NO

I like the idea of using photodiode or LDRs, but for this project I would like to do what I can with radio signals.

Light is not a radio signal but it is electromagnetic radiation, same as radio signals - just a higher frequency.

...R

What you can do is amplitude modulate the source signal and determine the phase difference between the signals received at each receiver. "correlation". If the distances between the three receivers is accurately known, you should be able to locate the source.

Perhaps this PDF will give you some direction: https://wireless.vt.edu/symposiumarchives/2015_slides/document.pdf.

Paul

You may find ultrasonic transducers a better approach.

Allan

How did you even come up with that very low 300 Hz frequency? It can't be from looking at how others do the same.

Ultrasound may be a good alternative, time of flight is much longer so that makes timing of signals (if you want to go that way) a lot easier.