Here is the question. The output voltage of an microcontroler is 3.3 V and max current is 100mA. How many LEDs we can wire together in series if we use 250 ohm resistor after each one. LEDs conductive voltage is 1.8V.


I know that if we wire resistors in series we must sum together the resistance of resistors. But i do not undertstand were i can use provided conductive voltage and max current. I hope you understood the question( my english is not the greatest). Thanks in advance

 

Welcome to AAC.

If you wire the LEDs in series, you must add up all the voltage drops, so after two you will not be able to supply enough voltage to them any more.

What are you actually trying to do?

 

Welcome to AAC.

If you wire the LEDs in series, you must add up all the voltage drops, so after two you will not be able to supply enough voltage to them any more.

What are you actually trying to do?

Its a homework quiz. Possible anwsers are 12, 14 ,16, 18.

 

So, do you know the difference between series and parallel?

 

Are those the ONLY possible answers? Are you sure that you copied the question exactly?

 

Its a homework quiz. Possible anwsers are 12, 14 ,16, 18.

Drop the course and enroll in a reputable school.

Hopefully either you haven't conveyed the problem correctly or the person that wrote it made a mental goof.

Are you sure that the question doesn't have a bunch of parallel branches in which each branch consists of one LED and one 250 Ω resistor in series? That would make a lot more sense.

What is the EXACT wording of the question?

 

Are those the ONLY possible answers? Are you sure that you copied the question exactly?

Sorry i misread it a little bit. We wire each led on a diffrent pin on the microcontroler.

 

Sorry i misread it a little bit. We wire each led on a diffrent pin on the microcontroler.

This still doesn't make much sense. If oyu can post the actual question we might be able to help, otherwise, good luck with it!

 

Sorry i misread it a little bit. We wire each led on a diffrent pin on the microcontroler.

Anything else [that you should know] and tell us about the microprocessor....

 

Answer is 16.

 

Assuming that the micro controller is going to use one led per pin, how much current does each pin need to supply. Figure it out for one pin first.

You know everything you need to do this. The source voltage is 3.3V. What does each LED drop? Then you have a 250 ohm resistor. What is the current through the resistor? What law of electronics is important here? Show us how you would apply it...

The final steps should become obvious once you successfully answer the questions above.

 

Answer is 16.

Hey, I thought you were supposed to ask the student to attempt an answer first before giving him one? He's probably online in class now and just got swatted by the teacher...causing a law suit of astronomical proportions...he gets thrown out and turns to a life of crime. geez

 

Answer is 16.

Really???

Its a homework quiz. Possible anwsers are 12, 14 ,16, 18.

 

TS still has to show how to arrive at the correct answer and most of this was revealed in post #11.

 

TS still has to show how to arrive at the correct answer and most of this was revealed in post #11.

Actually, all the TS has to do is select the correct answer on this multiple choice quiz. I don't see anything that indicates that credit on the quiz is contingent on showing any work at all. It's likely an online quiz.

The information in Post #11 gives a solid roadmap, but the TS can't get the answer to the quiz with it unless they understand the concepts well enough to follow that roadmap to get to the destination.

 

Sure hope the TS isn't the one designing my pacemaker after they graduate

 

Sure hope the TS isn't the one designing my pacemaker after they graduate

Let's be fair -- the TS didn't ask to be spoon fed the answer to his quiz problem (unlike so many of the folks that come here). Also, we don't know what level the course he is taking is. I'm guessing it's at the very beginning of his educational program and that this is all very new to him.