[Weather] conversion help

[Matthew Smith]

Quoth Tim Sailer at 11/17/2006 07:27 AM...

>> My main problem with my Lacrosse is that it only registers on every
>> other tip.  At the moment, I have a board in there that I made, based on
>> a Dallas Application Note.  I plan to replace this with one with a
>> Hall-effect device as I don't see that those wretched, fragile,
>> unreliable, reed-switches have a place in 21st Century engineering...
> 
> I'd be interested to see something like that. Would that work for
> the station itself too?

I see no reason why not.  Here's what we need to consider:

Reed relays are binary devices - they are either open or closed and thus
make a convenient input into a digital system.  (In my experience they
also have the states "contacts bouncing" and "broken" ;-))

Hall Effect devices have an analogue output, unless you get one that has
integrated electronics to deliver a digital output.  (The ones employed
in automotive electronic ignition systems may have this - I'm not sure.)

Thus, going from a switch contact setup to a silicon-based one would
require an additional analogue stage before we start feeding into the
1-Wire devices.  I haven't yet given this that much thought, but that
analogue stage may be as simple as a Schmidt trigger.

I can't remember how many reed switches there are in the (AAG) weather
station, but if we were to use Schmidt triggers, you could probably get
the pre-processing done taking up little more board space than a couple
of SO14 packages.

Just a few ideas there to get the ball rolling...

Cheers

M

-- 
Matthew Smith
IT Consultancy & Web Application Development
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