A question about the GND-Port of the GPIO - Raspberry Pi Forums

hello folks

i'm new raspberry pi community. bought rpi last week because i'm interested in gpio-interface.

problem is, i'm more of "computer guy" electrician, have basic knowledge electronics uri-triangle , on.

in future want use rpi monitoring sensor (*example*). told me, every sensor has external power supply (*like 9v battery*) need connection gnd gnd-pin of gpio, besides connection input port.

i've read gpi-pin can handle input of 3.3v. above damage gpio or conductor paths on rpi itself, need limit voltage data-pin of sensor, there 1 thing can't figure out. gnd-pin?

exsample of circuit diagram:

code: select all

<----------------- |		          | |		          | >-9v+-->sensor---> 	       |	   | 	       |	   | 	       |	   | 	       |	   | 	       |     gnd 	       |	   | 	     gpio<----- 

after sensor there still more 3.3v left. problem gnd-pin? have limit voltage 3.3v before connect gnd? this:

code: select all

<----------------- |		          | |		          | >-9v+-->sensor---> 	       |	   | 	       |	   | 	       r      r 	       |	   | 	       |     gnd 	       |	   | 	     gpio<----- 

hope, can understand problem, because english not first language...

in advance!

the ground sensor must connected ground on pi, common. there should no more 3.3volts across connection other gpio pin , ground.

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