Multiple Motuinos in an area 150ft x 150ft

[ijourneaux]

For a project I am looking at, I need to be able to collect information from 100 field devices. Just need 1 way communication but 2 way might be useful. I would not be transmitting much information.

Would Motuino be a good choice? What about battery life?
Ian

[Felix]

Moteino is offered with transceivers, so they can act as transmitters or receivers. I believe they would be a very good fit for what you need.
Battery life depends on how long you keep them awake and transmitting/receiving. There are several examples that achieve very low power here: https://github.com/LowPowerLab/RFM69/tree/master/Examples

When you have 100x devices, you will need to be aware that they cannot be all transmitting at the same time and very very fast, since only 1 can transmit at 1 time without causing collisions. It's like 100 humans talking in a room. If 1 talks everyone can listen and understand. If 2 talk then it starts to be a mess. Short messages take on the order of 5-15ms one way.

[ijourneaux]

In my case, the devices don't need to talk to one another they just need to talk to a "master". If all of the devices send a packet, how are the simultaneous transmissions handled, now do you schedule the transmissions to prevent collisions?

[Felix]

You would program the "master" with a specific node ID (typically Id=1 works pretty well and avoids confusion). Then all other nodes have ids > 1.
Collisions are avoided using a listen-before-talk feature. Basically the radio takes a signal strength reading and it waits for a certain amount of time while the signal is above a certain threshold. When the channel frees up it will transmit the packet.