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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.

[Reply #1 on:]

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).

[Reply #2 on:]

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.

[Reply #3 on:]

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.

[Reply #4 on:]

Thank you... that is what I was hoping to hear!

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

J.