[GreenKeys] Two very newbie questions

[Harold Hallikainen]

An answer to one of the questions:

It's a current loop. Either 60 ma for series pulling magnets or parallel
holding magnets, or 20 mA for series holding magnets.

We make a current source by using a high voltage and a high series
resistance. As long as the "load" resistance is small compared to the
fixed series resistance, the current is approximately constant (until you
open it with a keyboard).

Mark and Space date back to the Morse telegraph, which was originally a
recording telegraph ('til they found people could read the messages by
sound, which made the receive side a lot simpler). When there was current
through the loop, the tape would be marked. When there was no current, the
tape would not be marked (hence, a space).

So loop current = mark, no loop current = space.

Good luck!

Harold
Tokyo Japan

-- 
FCC Rules Updated Daily at http://www.hallikainen.com
Not sent from an iPhone.