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Hello guys I am currently working on a project. and I would like to turn on a GPIO pin when my LED on the circuit below turns on. I'm lost to where I should tie my input GPIO pin. please help. Thanks!

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Rikku
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1 Answers1

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Question

How to use a NPN transistor to "turn on" a Rpi GPIO pin?

Answer

Ah, you cannot "turn on" a Rpi GPIO pin. She won't listen to you, but you can ask her to behave as input or output! :)

In geek English:

  1. A Rpi GPIO pin can be in "input mode" or "output mode".

  2. An "input" pin can input/read a signal which can be High or Low.

  3. An "output" pin can output/switch a LED, eg, High to switch on, Low to switch off, (or vice versa, depending on circuit).

converter

I have drawn a circuit showing how to convert a loud (5V) signal to a soft (3V3) signal. The fair lady prefers a soft voice - loud voice can kill her! :)

converter 2

/ to continue, ...

References

NPN Transistor Tutorial - Electronics Tutorials

tlfong01
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  • used the wrong term.. that what I want to do.. to make GPIO as input.. – Rikku Apr 23 '19 at 07:32
  • I followed your digram above but it seems that I am not getting the expected output. – Rikku Apr 23 '19 at 07:34
  • Ah, perhaps you use the wrong resistors - not any resistor will do! Is the left most box working? – tlfong01 Apr 23 '19 at 07:41
  • yep it worked fine.. I replace it with another base voltage as trigger.. this is still somehow connected to the pump I ask about in the other question.. What I did was I used the voltage across the pumps wires run it throug a voltage divider circuit with 3V output and connected it to the transistor base as trigger. what resistor values should I use. – Rikku Apr 23 '19 at 07:53
  • I am confused. Perhaps you can update your question with a schematic. – tlfong01 Apr 23 '19 at 08:27