Wireless Communication Ideas

Question

Im going to be working on a project where I will need 2 nodes and one base station. To communicate with each other. I am going to be using an Atmel AVR for the processing on the base station. I have thought about playing with the Atmel raven stuff(for development) and then building my own circuit for the project. Just need to transmit data from the nodes to the base station when some inputs go off. Range is an issue about 100m needed(note this is a maximum Minimum that might be needed is only 2 or 3m). Due to the unknown length each time these will be used I don't want to wire them in. I would like low power with the possibility of the nodes being run of a coin cell.

• Is this a good way to go?
• Are there any alternatives to the Atmel Raven technology(Do microchip have an alternative)?
• Should I consider bluetooth or anything else for the wireless communications?

Answer 1

Digi has XBee modules which have the ZigBee protocol built-in and present themselves to your AVR as a simple UART, easy to interface. Digi has point-to-multipoint and mesh solutions. Modules are compact and reasonably priced.

Running off a coin cell may not be possible; RF transceivers are rather power-hungry (10s of milliAmps). Unless you have a very small power duty cycle. If for instance the device is switched on for 1 second every ten minutes you have a duty cycle of 0.17%.

Answer 2

The Nordic nRF24L01+ is an ideal chip for this application, used with small MCUs. They are widely used in wireless keyboards and mice, due to the very low cost. A range of 100m is feasible with decent antennas, out of doors. I've used the nRF24L01+ Spark Fun modules with PICs, here is some information on my hardware and software. They are very low power, and the operating voltage is ideal for use with a coin cell. I'm powering my hardware with two NiMH cells - about 2.5V. I know someone who is using the Nordic chips with an MSP430 device who is getting a battery life of a couple of years from coin cells in the remote nodes.

I've just ordered some very low-cost modules from here.

Several people have used them with AVRs, you should be able to find some source code you can use.

Answer 3

Based off your need for wanting it to be able to run off a coin cell, very low power is going to be much desired. This will probably have more to do with how well you code your micro (going to sleep when you aren't doing anything), but the MSP430 line is very good for low power. They also have the CC430 which is combination MSP430 and CC1100. The CC1100 is a sub 1 GHz wireless IC.

Having the two devices in a single IC makes it very nice to implement features like Wake on Radio since the device that is being woken is the same device that has wireless in it.

There are a few downsides to go with this method. Unless you want to make your own board with matching network and all your other option will be to buy a dev board that has that all done for you.

Also, by going with something like the XBee you can have the communication layer obscured to you. Meaning that you just throw data to it and it deals with getting it to the other end. This can be a good thing and a bad thing.

Answer 4

I haven't used ATMEL AVR but you probably want to go with something where Wireless etc. has good built in support already.. look up NESC.. it is like C and has a lot of built in API's for you to use to make your life simpler.