Author Topic: Question about $50 robot LED  (Read 833 times)

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Offline VegaObscuraTopic starter

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Question about $50 robot LED
« on: October 17, 2010, 09:17:01 PM »
I've completed my $50 robot, and everything on it works except the LED.  As I understand it, a 5v signal is supposed to go from pin 7 (vcc), through the LED and 320ohm resistor, and finally into pin 6.  This way when pin 6 is on, no current flows because both ends are +5v and there is no ground.  What I don't understand is how turning pin 6 to low is supposed to complete the circuit.  I'm very new to this, but to my understanding setting a pin to low sets that pin to 0v, but doesn't short it to ground.  Can someone clear this up for me?

Offline rbtying

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Re: Question about $50 robot LED
« Reply #1 on: October 18, 2010, 12:38:24 AM »
The "voltage" that is used in electronics is always a difference in potential.  GND is just a common reference, such that Vcc-GND = say, 5v.  Since we always measure a difference, then GND must be defined as the 0v point, since GND-GND = 0v.  Thus, any connection to 0v is a connection to GND.

When the controller mentions HIGH and LOW, it really means voltage of Vcc and voltage of GND, respectively.  Since all grounds should be common within a circuit, and so all voltages reference to GND, we just say 5v and 0v to make things simple. 


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