[aprssig] APRS event counter

[scott at opentrac.org]

I don't normally post firmware update notices for the OpenTracker to the
APRSSIG, but I thought one new feature was particularly cool, and
potentially useful for a lot of folks out there.  Thanks to VE3TK for
suggesting this - and my apologies for taking a year to get around to
implementing it!

Normally the interrupt input on the OpenTracker causes an immediate
transmission.  With the counter feature enabled, it increments a counter
instead.  The counter value gets reported in the comment text of each
packet.  It can either run forever (until it's powered off or it overflows
at 65,536) or it can be reset with every transmission.

It looks like this:

N1VG:!3448.20N/11959.67W> CNT00042

Or with everything turned on:

N1VG:/180340z3447.96N/11959.67W>000/011/A=000003 13.0V CNT00042 23C HDOP02.3
SATS08 Comment

The interrupt input is pretty fast, and touching a grounded wire to the pin
can cause tens or even hundreds of counts, so it's got a rearm delay
(debounce) timer.  The rearm can be anywhere from zero up to about 1/4
second, so it's safe to use with pushbuttons or other noisy sources.  If
you've got an OpenTracker with a 'transmit now' button, it's ready to become
a counter input button as soon as you set the checkbox.

Some suggested uses:

* Marathons like Bob's always talking about.  No need for a GPS, either.
Sit someone down at a checkpoint with a tracker and HT, and they click the
button once per runner.

* Geiger counter.  I'll be trying this one.  Set your tracker for a 5-minute
interval with counter reset enabled, and you get a 5-minute count value.

* Traffic counter.  I've had a couple of people suggest this.

* Lightning detector.  A simple two-transistor Darlington circuit will pick
up lightning strikes in the local area.

* Repeater activity montitor.  Also suggested by VE3TK.

You get the idea.  The output has an internal pull-up to 5 volts.  Grounding
it briefly triggers the counter.  It's triggered by a falling edge, not the
level.  You can implement a longer debounce period using a monostable 555
circuit if needed.

Existing OpenTracker users will need to get the new config program to see
the new options.  Click on the 'web' button to download the latest firmware
off the site.

If anyone's got other suggestions for uses, let me know and I'll try to add
them to the documentation.

http://n1vg.net/opentracker

Scott
N1VG