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Date: Fri, 30 Mar 2012 06:57:50 -0400
Message-ID: <CAPYb0EEdVqcSW3s=D8-EbTZA+_vQbm9p3bgxv=KVM0srDk7YCw@mail.gmail.com>
Subject: Re: [geda-user] Reed Switch vs Hall Sensor
From: Bob Paddock <bob DOT paddock AT gmail DOT com>
To: geda-user AT delorie DOT com
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Precedence: bulk

> Considering the low current you're putting through the reed switch I
> expect it will last a long time.

Check the data sheet for any switch that you use, even the giant 10+
Amp ones.  Some will have a *minimum* current rating, most don't have
it in the data sheet.
There has to be enough current to keep the contacts clean.  This
mostly shows up at manufacture time after cleaning the board or after
the switch had not been activated in years.
They build up an oxidation film.  To low of a current will not clear the oxide.

We use reeds by the thousands, as long as they are not physically
abused, they are glass after all, we've had no issues.

You can use an external magnet to bias a normally open reed to act
normally closed.

Allegro Micro sells booth active high and active low in the 3211 and 3212.
The data sheet makes the hysteresis curve look like the switch output
waveform, they are inverted from each other.

http://www.allegromicro.com/Products/Magnetic-Digital-Position-Sensor-ICs/Micropower-Switches-Latches.aspx

Some will work with either magnet polarity and some are unipolar.


-- 
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