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GPIO Start Low

Started by tpitman, Aug 12 2014 05:50 PM
gpio default

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#1 tpitman

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Posted 12 August 2014 - 05:50 PM

I would like to know if there is a way to set the GPIO to default to LOW on power up or if there is a signal on the headers that I can and with a GPIO that starts low.

 

I know I can invert the signals, but would rather not if I can find a cheaper solution.

 

The problem is that my circuit is a simple transistor to drive another device. Since the GPIO starts high the transistor is on by default. This triggers my device I am driving on power up and I can't have that.

 

Thoughts?

 


#2 Juzzer

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Posted 12 August 2014 - 06:04 PM

Pull it to GND with a 10k resistor


#3 tpitman

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Posted 12 August 2014 - 06:09 PM

I will give that a try. Thank you.


#4 Joshk

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Posted 12 August 2014 - 06:20 PM

It should be in a tri-state of neither on nor off during the netduino boot.  Your first line of code that mentions it defines which state it begins in.  Juzzer's suggestion should be all you need to keep your transistor in check during boot.


#5 tpitman

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Posted 12 August 2014 - 06:21 PM

When I used a 10k there was a little power allowed through the transistor I am driving. I went to a 1k. This seems to work. Does anyone think this will be a problem?


#6 Joshk

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Posted 12 August 2014 - 06:33 PM

That's probably fine.  Quit buying that RadioShack junk though!  haha


#7 Paul Newton

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Posted 14 August 2014 - 05:45 AM

Hi,

 

I solved this problem for my robot buggy by using opto-isolators.

I was using the Netduino Plus v1 whose pins are pulled high with weak pullups at reset.

These pullups were enough to activate the H-bridge circuit for my motors, but not enough to activate an opto-isolator's LED.

 

A single isolator was a small package so not a problem to fit into a small space, and they also make multiple devices.

The one I used was and still is £1.39 GBP in the UK from Maplin.

 

Its all written up on this WIki page: Driving high current / voltage loads.

 

Have fun - Paul


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