That is really rank, yes.  Good application though.

I suppose 'kicking the dog' would be inhumane as a trigger
mechanism in this instance.

I would suggest a simple one shot on the collar, and a little
RF loop receiver, receiving from a simple transmitter sending
a pulse every second.  The pulse would re-start the ramping on
the one shot and thus no change in the light output.  When the
pulse no longer comes, the collar shuts off.

So two 555s, two transistors and some support circuitry,and you've got it.
Very low range, perhaps a few meters, but should be good.

Only problem you might have is if there are several blind people in
the room, all the collars will stay activated if anyone is transmitting,
but this is a minor problem that isn't worth the additional circuitry to
solve.

Craig


>off after 1 minute with no reception?  Might do!  Whole new meaning to
>"Watchdog Timer" though <Boo Hiss, I know.>)
>
>  Mark, mwillis@nwlink.com
>