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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I don’t know where you got this but it is unlikely to work – Milliways 6 hours ago
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@Milliways I made it my self. So it is not possible to control a GPIO using a transistor switch? – Rikku 6 hours ago
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I don’t know what you are actually trying to accomplish. Are you trying to use GPIO to turn LED on? – Milliways 6 hours ago
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No. What I am trying to achieve is.. I would like to use the NPN transistor as switch for turning on GPIO Pin – Rikku 6 hours ago
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And what is supposed to turn the LED on? – Milliways 6 hours ago
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:
- A Rpi GPIO pin can be in “input mode” or “output mode”.
- An “input” pin can input/read a signal which can be High or Low.
- An “output” pin can output/switch a LED, eg, High to switch on, Low to switch off, (or vice versa, depending on circuit).
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! 🙂
Now I am making another step wise refinement to the circuit, to make it easier to do the following Agile oriented TDD (Test Driven Development), CIT (Continuous Integration and Testing):
- Continuous/Incremental Integration/Testing
- Structured/Functional/Loosely Coupled/Pair/Swapping oriented programming and development
- DevOp oriented Rapid Prototyping Documentation
The time has come to do a selfie walktrough, followed by a test plan with expected results, BEFOREtesting really begins.
/ to continue, …
References
NPN Transistor Tutorial – Electronics Tutorials
Reading suggestion – You don’t need to understand too much before you design something. I often design circuits without understanding what it does! 🙂 And as the mad engineer Heaviside says:
“Am I to refuse to eat because I do not fully understand the mechanism of digestion? – Oliver Heaviside
Newbie Troubleshooting/System Development Suggestion – tlfong01
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I followed your digram above but it seems that I am not getting the expected output. – Rikku 2 hours ago
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Ah, perhaps you use the wrong resistors – not any resistor will do! Is the left most box working? – tlfong01 2 hours ago
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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 2 hours ago
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