[aprssig] APRS bit I/O

'Scott Miller' scott at opentrac.org
Thu Jun 28 13:23:00 EDT 2007

Also kind of related... I got a bunch of Dallas DS2405 1-wire switches the
other day.  These are in 3-lead TO92 packages, like transistors.  I brought
the 1-wire bus from a Tracker2 out to a protoboard and dropped a DS2405 on
it, and it IDs just fine.  Drop another one in parallel, and it shows up to.
You can do that with however many devices the bus will support - I forget
the actual number.

So far I've had two problems to deal with before I can really make use of
arbitrary 1-wire peripherals like this.  First, you've got to uniquely
identify the chips - each has its own serial number, and the most obvious
approach would be to store each serial number in the T2's configuration.
That's 8 bytes per part, though, and it chews up a lot of configuration
space fast.

I think I've come up with a solution to that, though - with only 8 bytes of
RAM to store the last ID, I can scan through all matching IDs for a
particular part family in sequence.  So instead of specifying ID
05a8004000005812, you'd just say part #3 and it'd search for the third
matching part.

So now the big problem is what to DO with these things.  I mentioned an
expanded APRS telemetry format before - I suppose one approach to digital
and analog input would be to just scan every device and report it in
sequence in that format.  For output devices, though, maybe just a new
command?  Like SWITCH 3 ON to turn on the 3rd device of the 'switch' family.
There's still the issue of setting parts up for either input or output if
they're bidirectional.

I'm rambling a bit, so I guess what I want to say is that if anyone has any
clear ideas on how they WANT an APRS device to interact with multiple 1-wire
peripherals, let me know!


> -----Original Message-----
> From: aprssig-bounces at lists.tapr.org 
> [mailto:aprssig-bounces at lists.tapr.org] On Behalf Of Robert Bruninga
> Sent: Thursday, June 28, 2007 9:52 AM
> To: 'Curt Mills, WE7U'; 'VK / ZL APRS Users'; 
> vk4tec at people.net.au; 'TAPR APRS Mailing List'
> Subject: [aprssig] APRS bit I/O
> > > In the early days I used to peek and poke in the commodore
> 64.
> >
> > you can.  You need some I/O with digital outputs like a
> parallel
> > printer port or specifically some sort of digital I/O board.
> > Another way to play with I/O in this manner is to use the
> > handshaking pins on serial ports.
> Kinda related:...
> APRSdos has BIT/IO to the parallel port pins so that by APRS
> message remotely, you can read the status of any pin or turn on
> or off any pin.  This was for home-control ideas...  Bob, WB4APR
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