RE: [Development] Lights, an Idea any comments

["Dr John Tankard" <john@xxxxxxx>]

> what communication mechanism will you be using between the rabbit and
the
> pics?

At the moment is RS232 using SNAP (without checksum) but I was going to use
a very simple ASCII text stream because to decode SNAP you really need to
construct a state machine, which is ok but they can be difficult to debug
as
you don't know which state the system is in at any one time.

But I was thinking of using SPI or I2C which is for very short ranges but
very fast, however there is a USART on the PIC which we have selected, so I
could perhaps do a serial version if there was a lot of demand. However the
rabbit is so cheap, personally I don't think it would be a very good
solution, if the protocol/PC tools that we will have to produce are good,
which I am sure they will be there should not be any need to get direct
control.

>
> Reason I ask is I know a number of us like to have things
> contolled by a PC.

I would strongly advice against that, the Rabbit was going to handle the
local control, if you pass that over to a PC you would have no control over
the lights if the pc fell over.


> If the communication is compatible (ie a standard) then it might
> be possible
> for us to look at a version with direct PC control and no rabbit as an
> option. Or even for the PC to act as a back up and 'supervisor' for
the
> Rabbit (I realise the Rabbit's TCPIP comms will allow this but what if
it
> gets fried? ).

Its very unlikely, Keith's/my prototype ideas were based on a opto isolated
interface between the pic and the output drive. This would withstand a
considerable hit only taking out one channel, short of direct lightening
strike on a output (Almost impossible) then I think this would not be a
problem.

The Rabbit has, as Keith spotted, a isolation transformer to protect it
from
damage, in short if you have a problem its more likely that the network
card
in your PC would get fried.


John





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