You can use the RPD register on the nRF24L01+ to implement a stupid crude simple channel/frequency "scanner". The nRF operates in the ISM 2.4GHz - 2.4835GHz frequency band with 126 possible channels. Each channel takes up to 1MHz when the nRF data rate is set to 250Kbps or 1Mbps, and 2MHz for 2Mbps.
Anyway, I'm using this scanner to check if my second nRF is actully transmitting in the correct channel. It's also good for testing my TX code. Ah yes, I'm writing a nRF library for mchck.
Problem is, this 2.4GHz band is absurdly busy, you have everything in there, from channel hopping bluetooth devices to cordless phones. Come to think now, this scanner doesn't seem that useful... but wait! What if we shield both nRF's inside a box? That might work, but where are we gonna find a mini Faraday cage? I'm looking at you tinfoil.
- Small cardbox
Measure twice and cut one big tinfoil strip, enough to wrap the entire box if possible.
I started by wrapping the lid. Use the tape to not only fix the tinfoil but also to protect corners and edges.
With both sides done, start working on the bottom sides.
I folded the front in a way so it would help shielding the sides which were a bit short.
Aaand we are done. Last minor adjustments and corner tapering.
Unless you live under a rock the scanner will pick up all sorts of things, just keep pressing any key for a refresh.
Now in my case I have a Arduino Uno transmitting on a specific channel (16), and a mchck running the scanner. Time for the truth, with both inside the box, we launch scanner.
pause for dramatic effect
H O L Y C R A P look at that it works! ...ah, I totally knew that, no surprises... (totally surprised)
As you can see only a few bits around channel 16 are up.