retepsnikrep wrote:Chris
Wireless link good idea.
I have certainly been thinking about this and have already bought a couple of 433mhz serial data modules to tinker with.
I've played with a few 433MHz modules and they seem a bit more susceptible to noise than higher frequency units. I built a GPS decoder and time relay unit which I fitted in my loft (just because I had the parts to hand) and built a couple of nixie tube clocks which used the 433MHz time signal as a clock source (with onboard backup if the signal got lost)
The problem seems to be in the type of modulation, even quasi AM-FM modules still suffer a bit from it. The 2.4GHz band stuff, such as IEEE 802.15.4 modules use much more complex digital forms of modulation which are designed to coexist in environments where ordinary 802.11 WiFi is being used.
I'm differentiating between 802.15.4 and Zigbee here, enough to say that 802.15.4 is the standard which needs to be observed, and Zigbee is an implimentation of a comms protocol which complies with 802.15.4. There are other 802.15.4 protocols too, my favourite (but only just being born so not sure how good it is yet), is called 6LoPAN , which allows IP traffic straight over a 802.15.4 link. That's all to do with 'The Internet of Things' and would mean that each cell could have it's own IPV6 internet address and assuming you had the correct link hardware you could check on your batteries from anywhere in the world.
As for cost, you can buy ready to program Zigbee controllers for £12.50, wwhich have the zigbee stack built in so most of the networking stuff is handled within it. Or for £5.50 Microchip cells a 802.15.4 transceiver, which can be loaded with a Zigbee stack or their own licence free 'MiWi' stack and you just control it from another cheap pic over SPI.
I've only used a picAxe once for a University introduction to microcontrollers project, and they seem okay to use, but they might get expensive in large numbers, though I'm aware their price is falling as time goes by too.
I can see where you're coming from with the 433MHz stuff, and used primarily for the home link when the motor controller isn't creating interference you should be able to get away with it. But if yoiu got a problem you could always step up to another higher frequency band. The thing to watch out for with those modules is that some are designed so that you must use Manchester Encoding, which is one way to keep a dc neutral signal voltage, but many of the moduels ought to come with circuitry to handle this now, like the 'Smart Radio' modules from
www.rfsolutions.co.uk
I'm bogged down with a lot of other projects at the moment, and one of them could pay some bills so that will have to come first for now !
Chris
cured by a 0.1uf capacitor from Li-fepo4 negative to voltmeter negative supply rail. Supply is isolated anyway. That gives me a possible solution for the master interference.
