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How to not short circuit my Netduino ?


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#1 bgreer5050

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Posted 03 February 2015 - 07:23 PM

I am a beginner.  I have a relay that is opens and closes a set of contacts.  Can I send 5 volts from the 5 volt pin on the Netduino and send it thorough the relay to the #1 pin which I will declare as an Input ?  Do I need to set pin 1 to ResistorMode.PullUp and/or do I need to add a resistor to the circuit ?

 

I am afraid of shorting the Netduino, but I am not going from the positive straight to the ground so I have to believe it's safe.

 

Thanks

 

P.S. Will order a book today so I don't clutter the forum with such basic questions.   :)



#2 Chris Walker

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Posted 03 February 2015 - 07:55 PM

Hi bgreer5050,

You can send 5V to the digital input, but I generally recommend using a resistor in-line when you're tapping a large power source like that (to limit the mA).

If supplying 5V to a pin, don't use the internal pull-up/pull-down resistors though. They're 3.3V, and pushing 5V into a 3.3V resistor will cause 5V to leak into the 3.3V core system...potentially damaging the microcontroller.

BTW if you use 5V to create an external pull-up on pin D1, that's totally awesome too. That will limit your current as well.

We were all beginners once :) Welcome to the community, and please share what you learn and build with us if you can!

Chris

#3 asciiman

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Posted 04 February 2015 - 08:27 AM

hi Chris

 

Can i plug  2Amper or more to  7.5~9volt VIN power?

Or what is the limit of Amper ?



#4 Chris Walker

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Posted 04 February 2015 - 04:56 PM

Hi asciiman,
 

Can i plug  2Amper or more to  7.5~9volt VIN power?
Or what is the limit of Amper ?

The rating on your power supply is the maximum it will supply. So "2A" on a power supply means "this power supply will supply 0.0-2.0 amps of power". No problems there.

The board will only draw up to around a maximum 800mA under normal conditions. That's where its 5V power regulator tops-out rating-wise. So any power supply over 800mA (and really...any power supply over 500mA) is just giving you extra margin.

Chris




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