If you have to update whenever any machine changes state, polling will not work since a machine may change state more than once between polls, especially if you have 40 machines to poll. Nor will just letting each machine transmit as it changes, as you are sure to have collisions and lost data. And, a loop which polls each of 40 machines will violate every European regulation on how often any one transmitter can transmit. OTOH, if you can accumulate counts locally and transmit the total periodically, polling or independent transmission will work. An occasional collision can will not matter as an accurate count can be sent with the next transmission. It all depends on how frequently each count changes and whether you need to have each change registered immediately. If you can live with independent transmitters, you can use much cheaper hardware. What distances are involved? As this sounds like a factory floor, my guess is it's not very RF friendly with lots of metal surfaces and maybe lots of interference. I'd look at a wired RS-485 network.