NRF24L01 module help for IoT project!

[Shehryar X]

I want to use a NRF24L01 module to communicate between to Arduino UNOs, but I also need the signal strength since I want to calculate the distance between them relatively precisely. Is there another module you guys know of that does both data transmission AND exposes accurate access to signal strength?

[mfalkvidd]

@shehryar-x the rfm69 will give rssi values. What does "relatively precisely" mean for your use case, and for what distance? For precision below 5-20m (for distances <50m you will likely need to measure round trip time very accurately.

[Shehryar X]

@mfalkvidd I will need to get around 1 - 2 meter distance at the very least. Can you elaborate on how to measure the round trip? I think it can only send 32 bytes of data per trip, and I also have other data to transmit; so how would sending a large packet work?

[mfalkvidd]

@shehryar-x measure: send a message (as short as possible) and measure the time before you get the acknowledgement. Send many such messages, use the shorest time. Calibrate at a few distances. But the radio signal travels 300m per microsecond so you'll need to be able to measure very accurately. I don't think it can be done on the cpu.

More than 32 bytes (27 with MySensors): what type of data are you sending?

[Shehryar X]

@mfalkvidd I need to minimize costs, so is there any way i could measure the time that accurately without purchasing external clock hardware? Or any other accurate way / sensor that can track the proximity of an object?

[mfalkvidd]

@shehryar-x I am not aware of any cheap radio-based solution. Ultrasonic distance sensors and ir distance sensors are affordable but need to be pointed to measure distance.

[Yveaux]

@shehryar-x try ti tdc7200

[OldSurferDude]

light travels at about 30cm/nS. The Uno can capture +/- 1μS at best, so, at best, your accuracy will be +/- 30m.

In the nRF24 library I'm using, there timeouts, meaning that you will never know exactly how many μS a network.read() will take, adding multiples of 30m to the best case.

+/-2m is not possible using an Uno and any radio.

Try two GPS's, one on each module with each Nano and take the difference between the two. I'm pretty sure that would meet your spec. (Amazon) Yes, one GPS is rather inaccurate, but the inaccuracy is the same on two relatively close (google "differential GPS") That would be a cool project! And! you could log the track! You can find less expensive modules on AliExpress (caveat emptor and 20-90 days delivery)

[mfalkvidd]

I just stumbled on a module that claims to be accurate to 10cm/4in https://github.com/thotro/arduino-dw1000/wiki
Range is 300m.

https://datasheet.octopart.com/DWM1000-Decawave-datasheet-129251925.pdf#page21

[OldSurferDude]

(yeah, this is really old in tech years, but I post in the event someone stumbles upon this.) I actually tried the GPS suggestion. I was wrong about the error between two identical GPS's. It's quite large. Check out the other suggestion first.