Which radio module(s) should I use for my project?

I´m trying to build a little robot, which would drive around in my garden, and always know its location. To achieve this, I thought about planting 2 stationairy radio transmitters in certain spots, which would be a known distance apart. Now for every "step" the robot makes, it should get a signal from the transmitters. The first one starts and the robot is supposed to rotate an antenna towards the signal, by measuring the RSSI and saving the angle of the strongest signal. Then it should send a "OK" message, and the process should be repeated with the second. After that, it can use the known distance between the 2 emitters, and the 2 measured angles, to calculate its position on a 2D map, relative to the 2 emitters. Now I of course want to get the best radio transmitter (and receiver) for the project. It should be able to read the RSSI, and it should have a range of at least 5 meters. The nrf24l01 for example is just able to check, if its over a certain value, and will then give out a boolean. Obviously too vague for me. Also, I´d like to know what I could expect from said robot. It would be used outside, however, obstacles such as trees, bushes or chairs will still exist. Would the strongest signal still be in a straight line, when going through a tree, or could its reflection from a wall nearby be stronger? And if so, what could I do, to make it work better? Please help me, because I don´t want to make the wrong choices when I´m ordering the parts.

Thanks in advance!

Sorry but what you describe is extremely unlikely to work. Wireless signal strength if just not sufficiently precise.

You could do it with a couple of "lighthouses" and a rotating detector (photo diode) at the end of a small tunnel so that its angular range of vision is very restricted.

For larger distances there is, of course, GPS.

There is a system called Pozyx which could probably do what you want but I believe it is not cheap.

...R

Welcome to the Arduino forum!

You do realize you are experimenting, so ANYTHING you order may or may not do what you want.

You mention the robot will rotate an antenna to determine the two signal strengths. I must ask you what type of antenna are you thinking of that will give you a beam width small enough to give any indication of actual direction? Any antenna has major and minor lobes and nulls in it's pattern of receiving and transmitting. The best would be a parabolic dish and the frequency would be in the 10gHz band. Do you know how large and heavy a dish and it's rotating mechanism will be? There are NO hobby transcievers usable with an Arduino that operate higher than 2.4 gHz. Please Google directional antennas for that frequency. They are neither small nor cheap, unless you build it yourself.

Paul

I´m trying to build a little robot, which would drive around in my garden, and always know its location.

Start by defining what you mean by “its location”. To what accuracy do you need to know this?

This idea comes up at least once a week, indoors and out, with very few, if any people reporting success.