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Topic: Splitting outputs between two 5v microcontrollers and a pi (Read 87 times) previous topic - next topic

Jas15

I currently have a microcontroller outputting high or low on several pins and another microcontroller reading the state of those pins.  They are both running at 5v.  I would like to connect a raspberry pi to the same pins to read high or low states, but the gpio pins of a pi can only support 3.3v.   What I need to do is have the voltage remain at 5v for the connection between the 5v microcontrollers, while dropping the voltage to 3.3v for the pi.

I have connected the output of an arduino microcontroller to a pi in the past using resistors to create a voltage divider, but that was a direct connection.

In this situation however I am trying to tap off of an existing connection between two 5v microcontrollers and I am not sure how to do that.

alesam

Connect 5V controllers directly but pi through a voltage divider.  
Don't say "Thank you", just click on 'karma [add]' instead.

Jas15

Connect 5V controllers directly but pi through a voltage divider.  
If there is a direct connection between the two controllers, wouldn't all of the current go through the direct connection and none through the voltage divider?

alesam

Microcontroller's and RPi's inputs detect voltage not a current. And they have a very high impedance. So each input pin consumes very low current. Unless you going to connect hundreds of inputs to one output you can ignore problem with insufficient current.

Like if you have a power strip with plugged table lamp. What happened if you plug a few more  table lamps into the same power strip?  
Don't say "Thank you", just click on 'karma [add]' instead.

Jas15

The impedance on the inputs of the microcontrollers was what I was missing, I think I can complete this project now, thank you.  I appreciate your analogy also.

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