How does LED Brightness vary with current? Project help

[deleted-331468]

I don't get the procedure. If we're supposed to connect the light-to-voltage converter to the battery pack then are we supposed to disconnect and rebuild the circuit on the breadboard? Because if we are already connected the converter to the battery pack then why does it say insert the converter into the breadboard? I'm only confused on this part.

[deleted-249560]

I went back and reread it and you're right - that is confusing.

The procedure starts by explaining what you'll be building (steps 1-4), then it explains in step 1 (again) how you read the output. Finally step 2 says to follow steps 2a through 2e to build the circuit on the breadboard.

We should clarify that. Thanks for pointing that out.

Howard

[deleted-331468]

So I'm supposed to follow steps 2a-2e to build the circuit?
Three more questions: What does it mean by terminal? What is a power bus? How are we supposed to connect each terminal to a power bus?

[deleted-331468]

Why do we need repeat the investigation with a second LED?
Also are we supposed to make the graph a line graph and are the results for both LEDs supposed to be on the same graph?

[deleted-331468]

In the building the light detection circuit section what is the power pin? The middle pin of the converter is connected with the positive power bus, but a power pin is also supposed to be there. The ground pin is connected with the ground wire of the battery pack and the output pin is connected with one end of the resistor, so what's the power pin? What exactly do you mean by point the LED at the sensor window? What is the sensor window?

[deleted-249560]

The procedure is asking you to connect the red and black wires from the battery back to the 'power buses' on the breadboard. If you looked at the breadboard tutorial (https://www.sciencebuddies.org/science- ... d-tutorial) you saw that on the edges of the breadboard are rows that are marked red and blue. Those are buses. The idea is that you can connect the battery (red wire to red and black wire to blue) in one hole of each bus and then connect any number of wires to that bus. So let's say you need to connect 4 things to the red wire of the battery: put the red wire from the battery back into the red bus, then put the 4 wires from the other 4 connections into other holes in the bus.

The instructions refer to terminals which is a bit confusing, but it's simply trying to say to use the red wire from the battery back in the red bus and the black battery in the blue bus.

The light sensor chip has a window in the center that receives light. That's what the instructions are referring to.

Howard

[deleted-331468]

Thanks, but why do we need to test it twice?

[deleted-249560]

In scientific experiments you always repeat something several times (if possible) to make sure that your results aren't the results of a mistake. When you do this experiment the second time you should get the same results. If not, then you may have done something wrong and you'll want to try again.

[deleted-331468]

And what is a power pin?

[deleted-331468]

So in the building the LED Circuit and measuring the LED current you repeated how to build it and there was a contradiction. In the building the LED Circuit you said to use a clip lead to connect the shorter lead (cathode) of the LED to the black wire of the battery holder, but in the measuring LED current section you said use a clip lead to connect the shorter lead (cathode) of the LED to the red probe of the DMM and then went on to say use a clip lead to connect the black probe of the DMM to the black wire of the battery holder. So am I supposed to follow the measuring the LED current section or building the LED circuit section?

I am guessing I'm supposed to follow the measuring the LED current section because that tells you how to hook up the DMM to the circuit.

Also in the building the light detection circuit section what is the power pin? The middle pin of the converter is connected with the positive power bus, but a power pin is also supposed to be there. The ground pin is connected with the ground wire of the battery pack and the output pin is connected with one end of the resistor, so what's the power pin?

[deleted-249560]

As described in the procedure, pin 2 of the sensor chip (middle one) is connected to the positive side of the battery, or the source of power. The text refers to that as the 'power pin'.

The procedure describes how to do the experiment with one meter. Connect the led and resistor without the meter and use the meter to measure voltage. Then disconnect the meter, switch it to current mode and connect it in series with led as described. If you have two meters you can just connect one in series and do the whole test that way.

[deleted-331468]

So the power pin is the middle pin?

I don't get what you're talking about in the second paragraph. What meter are you talking about? I'm referring to the section about measuring mA, but there are two different instructions to make the circuit for measuring mA. One is in the actual building the LED circuit section and one is in the measuring the current section. I just want to know which one to follow.

[deleted-249560]

If you only have one multimeter you have to follow them both. You wire the LED *without* the multimeter and use the multimeter to measure the voltage as it describes in "Measuring LED Light Output". THEN you disconnect the meter and connect it in the LED circuit as described in "Measuring LED Current" and measure the current through the LED.

If you have access to two multimeters you can simply wire the LED once as described in the "Measuring LED Current" section with your second multimeter measuring the sensor output voltage and do both part of the experiment at the same time.

Howard

[deleted-331468]

Thanks