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cameron
08-14-2008, 12:16 AM
Hi,

On Page 64 on the ebook whats a micro controller it shows a multi direction LED. As i understand it you have to put a resitor before the anode of the LED to stop it sucking up all the current and burning out. My question is when you change the polarity of the circuit using the basic stamp to change the colour of the LED dont you have to move the resitoer to the other side of the LED because current is flowing in the oppersite direction?

Thanks,

Cameron.

SRLM
08-14-2008, 01:24 AM
The way that the circuit is set up is in series. If you remember from your high school physics class, resistance in series is added up. It doesn't matter which dirrection the current is going. Think of it this way: on one side of the LED is ground, the other High. Now the LED needs a difference between the two of a couple Volts. It doesn't matter what the voltage is relative to the rest of the circuit or the world. Now the LED may be operating between, say, 9 volts and 7 volts. Thats a drop of 2 volts. In the other dirrection, it operates from 2 volts to 0 volts. That too is a drop of 2 volts.

In short, it doesn't matter what order resistors are placed in when placed in series: the total resistance is the sum of the parts.

Steph Lindsay
08-14-2008, 01:36 AM
That is a good question, Cameron, one we should address in the book. I will add a note to my revision list for the next update.

I hope you are otherwise enjoying the book.