Chartplotter alarm
 

Gordon wrote:
pirate wrote:
I had a very pleasant conversation with a fellow at SH yesterday. I
explained what I wanted to do re. the flush mount and he said it would
work. He volunteered to send screws and template to me. I also told
him about the internet discussions about alarm volume. I told him
that like me, many "geezers" can't hear all that well and suggested a
jack for an external speaker be added or a louder alarm with a volume
adjustment. He thought is was a very good idea and was going to
forward the info to the manager of product development.

Got the schematics from SH and guess what? There is an external alarm
driver that they didn't bother to bring out! It is pin 12 of p61 which
is the I/O connector on the mainboard. Appears to be a testpoint also
(TP61-12). This is an open collector of a driver transistor.
Hook a piezo buzzer to it and 12vdc to the other end of the piezo and
it should work!
Now to try it.
Gordon

For permanent installation I'd add some isolation, like an opto-isolator
between the main board and the outside world.