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Simple switch detection circuit - don't want to fry board


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#1 RobFromLI

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Posted 21 November 2014 - 04:55 PM

Hi all,

 

I am a very experienced programmer who has a little bit of electronics knowledge.  Basically I've fooled around in the past with some simple switches, lights and motors and maybe a resistor or two.

I'm looking to hook my netduino 2 plus to a normally open circuit and trigger it to bang a web service on my pc when the circuit closes.  I have the code roughed out using the on board button and now I want to code/test just using a short wire or switch before I hook it up to the larger circuit. 

I've done a good bit of searching and found this http://arduino.cc/en...utton_schem.pngwhich is part of this tutorial

http://www.arduino.c...Tutorial/Button

 

I just want to make sure before I try this (assuming I hook everything up properly and protect against static and all that) - if I hook a 10k resistor between digital input 1 and ground as a pull "down"(? or up? but I think down?) and then have a switch that connects the pin to 5v, I won't fry anything, is that right?

 

Do I have to have the pin set to the proper mode when I connect the wire in order to avoid frying something?  In other words if I have a bug and the pin's set to output but I put 5v on it, will it fry then?

 

Can I uses 3.3v, is that any safer / better?

 

TIA

 

Rob



#2 ShVerni

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Posted 23 November 2014 - 05:47 PM

Hi Rob,

 

You're perfectly on point that your circuit it will work just fine. The Netduio's digital pins are 5V tolerant even though they operate at 3.3V. That is to say, they output 3.3V signals, but will accept 5V or 3.3V signals as input. That said, it certainly wouldn't hurt to go with 3.3V, it will even save a miniscule amount of power (though really, not enough be worthwhile is all but the most power sensitive applications). As a word of caution: the Netduino's analog pins, when not operating as digital pins, are NOT 5V tolerant, and using a 5V signal could damage them. To be safe, I try to only use 3.3V signals with the analog pins.

 

As a point of nomenclature, a resister tied to ground is a pull-down (down to 0) and a resistor tied to VCC is a pull-up.

 

Good luck!



#3 RobFromLI

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Posted 24 November 2014 - 02:33 AM

Hi Rob,

 

You're perfectly on point that your circuit it will work just fine. The Netduio's digital pins are 5V tolerant even though they operate at 3.3V. That is to say, they output 3.3V signals, but will accept 5V or 3.3V signals as input. That said, it certainly wouldn't hurt to go with 3.3V, it will even save a miniscule amount of power (though really, not enough be worthwhile is all but the most power sensitive applications). As a word of caution: the Netduino's analog pins, when not operating as digital pins, are NOT 5V tolerant, and using a 5V signal could damage them. To be safe, I try to only use 3.3V signals with the analog pins.

 

As a point of nomenclature, a resister tied to ground is a pull-down (down to 0) and a resistor tied to VCC is a pull-up.

 

Good luck!

 

 

Thanks very much!  I will proceed with my project and I'll try to report back when I've succeeded.  Thanks for the help!






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