RF Communications

I am planning on a project involving a bunch of Nordic nRF24L01+ modules talking to each other and I have some questions. These are going to be used in a “wearable” setting where a bunch of dancers will be wearing them.

The idea is that one of them will act as a master, sending instructions to the others which will all be in receiving mode only. What I’m wondering are:

A) in a constant moving, spinning target, how well will these perform communicating with each other. If the master is pointed away from the rest, will they still be able to pickk up the signal? If I put these on the backs of the dancers, and if two of them are some distance apart facing each other, the modules would be out of line of sight from one another. How well will that work?

B) if I can manage to make them work, the next question is the actual communication and how to implement it. Do I transmit data and wait for the specific slave to respond before moving on to the next one? With a bunch of them, that could take a while for all to respond.

I’ll probably have more questions but for now let’s start with that …

A) Its relatively low frequency RF, not high frequency line if sight microwave/GPS frequency; it will work just fine.

B) "the others which will all be in receiving mode only" vs "transmit data and wait for the specific slave to respond" Which one is it to be? Either way, unless you are sending gobs of data, the ack back from the slave will instaneous compared to the time it takes for the dancer to react to a visible message, or vibration, or electro shock or whatever they are to do.

Sorry, I should've been clearer. I was watching a practice and using my phone to post. How the modules are configured will depend on how I communicate with them. I will either have all but one in receiving mode only, in which case the master will send out a signal to all the slaves and hope they all receive it and react accordingly. OR, the slaves will be listening and when they get a signal that's specifically for them, they will send back an ACK to the master so that it knows to move on to the next slave.

The thing is, it's a light show, and the job of the master module is to tell the slaves when to change the sequence of light display on that dancer. So that's why I'm concerned, with all the movements and all, should I expect a communication breakdown at some point? Should I have the master wait for an ACK, or just assume the slave has received the command or commands. And, since it's working in the 2.4GHz range, should I also be concerned with interference of other stuff on stage ...

Hmmm. 2.4GHz and motion???

Try talking on your cellphone and doing same spinning. Any problems??

Not sure about doppler/phasing effects. But motion on a bike/car seems no problem???

terryking228: Try talking on your cellphone and doing same spinning. Any problems??

For me, no problem, but some people will tell you their calls get dropped. grin

But, point taken!

…when using 2.4GHz modules with antenna built on pcb you have to consider:

  1. maximal distance between dancers (the modules have limited range)
  2. position of the antenna (those antennas are directional, they have minima in signal strenght when rotating)
  3. the distance of the antenna from the dancers body (when very close ie. <1cm the signal is attenuated by the body)
  4. jamming from a happy spectator :slight_smile:
  5. baterry voltage levels changes.

The change of phase and doppler is not to consider unless the dancers move themself on the stage with speeds of thousands of mph (probably not the case…).p.