What about RS485? Can go long distances, and is well documented and
understood. There exists RS485 devices for PCs, etc.
There would need to be a uC (PIC, Stamp, etc) at the HVAC end of things to
read the commands from the network and perform the actions via relays,
etc, but that is about it.
But then again, it could be susceptible to the same types of network
problems. ie: if the line gets cut it goes away. The uC on the HVAC side
of things could require a constant flow of commands or it will go into a
fail-safe mode and shut everything off. ie: must receive a "stay-running"
command every 30 seconds or 1 minute or it will shut off..
Yet another idea would be to have similar uC, but it would be controlled
via i2c. You could then have the uC controlled by a TINI (via the onboard
i2c port). So this way you issue commands just via the network. (ie:
TCP)... This removes the RS485 problem and requires a TINI.. Again the uC
can have failsafe features that if it doesn't hear from the TINI in a few
seconds it will shutdown. This way the TINI could be responsbil for
refreshing the status of the uC, and not the main computer. The main
computer just sends it's wishes the the TINI and considers it doen...
hope that all made sense...
(one of the lurkers...)
On Thu, 1 May 2003, Vadim Tkachenko wrote:
> Hello lurkers,
> As the time goes on, I become less and less happy with the idea of using
> DS2406 to control the AC. Reasons:
> - they are a part of a sensor network, therefore when (not if) the
> network gets damaged, they go down too. Alternative is to install
> another 1-Wire adapter, but this is either a hassle, or outright not
> - DS2406 are known to react funny to power outage - the circuit state
> after power restoration is not predictable nor it is stable
> - 1-Wire latency gets in the way when sensor network grows larger
> That's all I can think of now, but it is more than enough to justify
> looking for a better way to control multi thousand dollar hardware.
> Anybody has a better idea?
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James A. Russo