Hi I am searching for a cheap wireless solution to connect up to 80 Arduino based devices (ATMEGA328 and ATTINY85) in an range of 100 meters to a wireless network. The devices get and send data. The speed of data transmission can be very low. Xbee seams to be to expensive. The devices will be not connected to each other, only to the hotspot.
Any suggestions?
RF24L01 modules are cheap. Take a look at this: http://maniacbug.github.com/RF24Network/ But I think the library doesn't works with the attiny.
With the nRF24L01, do I need only one transceiver module on each arduino device and only on on the base station (hotspot)?
newuino:
Hi I am searching for a cheap wireless solution to connect up to 80 Arduino based devices (ATMEGA328 and ATTINY85) in an range of 100 meters to a wireless network.
Are all the devices going to be 100m from the 'hotspot'? I don't get anything like that sort of range using nRF24L01+ transceivers with standard antennas. It's possible to get boosted antennas but I don't know what sort of range increase is possible with those. If the units are going to be spread out such that each one is in range of one or more others, with some in range of the hotspot, then you can use a 'store and forward' scheme to relay messages back to the hotspot.
The nRF24L01+ are a cheap and easy to use radio link, but the message capability (at least, using the RF24 lib to drive it) is somewhat quirky. Although the number of available channels is huge, each transceiver can only listen to six channels at once. You can have multiple senders on the same channel, as long as you have a scheme for dealing with collisions. In practice this means you need to build your own message addressing scheme on top of the RF24 lib. Although each message transaction is nominally bidirectional (the sender sends a message and gets a response back) the response has to be pre-set and cannot be worked out 'on the fly' by the receiver. This makes it difficult to use conventional command/response type semantics when linking these units together. I did eventually get a self-organising tree working, where each unit negotiates the shortest route to the hotspot via its neighbours, but it took quite a lot of fiddling to get it working. While you're doing this, bear in mind that the RF24 transceivers don't seem to cope well with messages containing long sequences of bits with the same value (they seem to lose sync), so design your addressing scheme and message format to avoid that.
A solution could be to align the devices with nRF24L01+ transivers in a row. 2m distance from each other.
So the data will be transmitted from the nearest to the base to the next. If the last device has done its work it will sent the data to his neighbor and so on until the data from all devices has reached the base.
Is there a limitation (devices)? Can I can "hard wire" a unique ID to each device? Is a option to set the wireless to any "sleep" mode to save power? Maybe to check every 10 Minutes if there is a incoming Signal.
I think you first need to chose a (network) topology. You can prove that it works by wiring the nodes up. Making it wireless it just a matter of replacing the wires with RF transceivers.