Hi,
Quick intro - I'm a linux progammer/sysadmin. I play with AVRs (ATMegas mostly) for fun and have got on well with them.
I'm looking to set myself a moderate project next year which is to do with home automation (thermostats etc). Although I *could* use RS485, CAN or some other wired links, I rather fancy playing with radio for the educational value.
So I'm after something that's:
1) Cheap hardware - say $20 or less for the radio module;2) Usable data rate around 100kbit/sec
3) Range: 10-20m through brick walls (no foil/rebars etc)4) Half duplex
Did ask this on sci.electronics.design - they produced some good ideas (summarised below) but suggested asking here too...
So it seems to be a toss up between:
a) simple tincan radio transceiver (433/868MHZ or somesuch unlicensed band in the UK) that can send a 0 or a 1 over the carrier by flipping a digital input.
b) Zigbee, eg an Xbee module.
a) Involves obviously, timing sensitive programming, computational overhead and supporting some form of OSI Layer 2 in software. This is doubtless the cheapest solution assuming I don't cost my time (hey it's a hobby).
b) By my reading, Zigbee does all the packet framing, collision detection/retries and deals with all the wibbly timing sensitive stuff for you. Cost seems very reasonable for what it does, but obviously puts a high capital overhead on a module based on a cheap-as-chips AVR.
So the question is: what would you do, assuming cost was an important priority, or perhaps what have you done successfully, along these lines? Maybe there's a c) option I haven't considered...
I should note I don't have spectrum anaylsers/debuggers to hand, though at a pinch I could go to an ex company and use theirs - but not too many times! So I have to work blind most of the time as far as the RF stuff goes, preferably without Ofcom knocking on the door ;->
Many thanks for any random thoughts :)
Cheers
Tim