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Author Topic: magnetic reed switches - understanding ratings  (Read 439 times)
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My first Arduino project is a garage door open notification/control. I'm using a Uno and Ethernet shield; to determine whether a door is open/closed I've found some magnetic reed switches.

On the package of the switch it states 500mA @ 12VDC. The data sheet (http://www.mode-elec.com/pdf/switches/47-600.pdf) has the following:
  • switching current (max): 0.25A
  • switching voltage (max): 30VDC
  • insulation resistance: 100Mohms Min

My question is: can this be driven from one of the digital pins of the Uno, or do I need to use an opto-coupler to drive this from a 12V power supply? Does it really require 500mA?

many thanks,
   J.
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Phoenix, Arizona USA
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I think you're confused as to what a "magnetic reed switch" is. It is a switch that is actuated by a magnet. It isn't driven by anything (it can't be switched by the Arduino - unless you wire up an electromagnet to switch it, then you've just made yourself a relay).
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Sorry, I didn't mean "drive". I want to hook the reed switches to an digital input pin to sense whether the switch is closed or open.
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The 500ma refers to the MAXIMUM current that the switch can carry.   Since a reed switch is a sealed device it will happily switch extremely small currents (several microamps).   It's generally considered that many switches need a decent current flow so that the arc of breaking "wipes" the contacts clean, but this limitation doesn't apply to reeds.
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Thank you... that is what I was hoping to hear!

I will post further (hopefully) successes as I proceed with this project.

J.
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