# LED Beginner Project

Discussion in 'Homework Help' started by RdAdr, Feb 13, 2016.

1. ### RdAdr Thread Starter Member

May 19, 2013
214
1
How can you make a simple circuit with a LED, a resistor and a battery without using a soldering gun and without using a solderless breadboard?

Or maybe with two batteries and connecting the batteries in series.

I think with crocodile clips.

Last edited: Feb 13, 2016
2. ### djsfantasi AAC Fanatic!

Apr 11, 2010
2,899
870
I have many questions for you. What type of battery are you using? Do you have (or can get) a battery holder? Do you know the characteristics of the LED? Or have you read the datasheet? What is the resistors value? What is this for?

The short answer to your question is that you can, but you need some additional information if you want to know how. Alligator clips are one way. Wire wrapping (not the traditional type) or even with brads in a board,,,

3. ### RdAdr Thread Starter Member

May 19, 2013
214
1
For example, let's say that I have an LED that has a forward voltage of 2V and a max current of 15-20 mA.
And I use a 3V battery.

Then I need a resistor that will take the difference of 1V. And I choose it based on I=(3V-2V)/R, where I=15mA.

This would be the simplest case.

What I really want is to have 6 LEDs connected to a 9V battery, where 2 are in series and the other 4 in parallel two by two (after the two in series).

And I thought that on these LEDs I will have 8V. So I need another resistor to take the rest of 1V. And I calculate R so that the current is 15 mA.

My problem is now that through the parallel LEDs will go only 7.5 mA.

Will this be enough to light up the LEDs? Maybe they will show some little light.

And as components I would need a 9v battery, a 9V battery snap on connector, wires, alligator clips, LEDs. And that is all.
It would work?

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Last edited: Feb 13, 2016

Feb 19, 2010
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5. ### RdAdr Thread Starter Member

May 19, 2013
214
1
In the case I find this in the store.

I take the screw out, I put the wire inside, then I put the screw back on?
And the screws are all connected beneath the white plastic?

Can you draw quickly in paint over the picture how one resistor in series with other two resistors that are in parallel would look like? Plus the battery of course.

Oh, now I see the picture from amazon. So the connection between two wires is made like so. The first wire i stick it into the top hole. The second wire I stick it into the lateral hole corresponding to the top hole. And connection is made. Right?

Last edited: Feb 13, 2016
6. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,500
511
You don't NEED to take the screws out. You just loosen the screws, put the wire in, tighten the screw.
Each vertical section is connected inside.

Also note the holes between the vertical sections. Once you figure out all the connections, you can mount this thing on some panel or inside a box.

7. ### RdAdr Thread Starter Member

May 19, 2013
214
1
Aa, so I need two vertical, top holes to make a connection between two wires. What are the lateral, side holes for?

8. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,500
511

The holes between the vertical sections are for mounting the whole thing to a panel or inside the box.

9. ### RdAdr Thread Starter Member

May 19, 2013
214
1
Ok, thanks. But if I can't find this, the crocodile clips would also work, right?

Feb 19, 2010
3,500
511
Sure.

11. ### WBahn Moderator

Mar 31, 2012
18,079
4,917
Do NOT put LEDs in parallel. This is a very bad practice.

Just put three LEDs and a resistor in series and make two of those chains. Size the resistor to give you the current you want. Your total current draw from the battery will be twice that.

12. ### RdAdr Thread Starter Member

May 19, 2013
214
1
I know. But this project is for my little cousin from her school. Her teacher said to have that kind of circuit. Maybe the purpose is to see that putting things in parallel divides the current and thus you see less light.

Last edited: Feb 14, 2016
13. ### MrChips Moderator

Oct 2, 2009
12,623
3,451
You can put together circuits using simple and readily available material - a piece of softwood for breadboard, woodscrews and washers for terminals. Use metal paper clips to make a simple switch.

atferrari, RdAdr and djsfantasi like this.
14. ### GopherT AAC Fanatic!

Nov 23, 2012
6,300
4,020
Here. You can skip the magnet in the instructions if you don't need it to stick to a surface.

You can skip the resistor in your circuit if you use a high impedance battery (e.g. button cell).

http://www.instructables.com/id/LED-Throwies/

RdAdr likes this.
15. ### RdAdr Thread Starter Member

May 19, 2013
214
1
I got a 9V connector. Which wire is positive and which negative? There are two wires: red, black coming out of it.

The hexagon is plus and the circle is negative. But I care about the wires.

My guess is that red is positive.

LE: yes, is red. The LED is On.

16. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,500
511
It is marked on the battery.

17. ### RdAdr Thread Starter Member

May 19, 2013
214
1
I know.

Then you put the connector on the battery. From the connector it comes out two wires. The connector is covered in some black plastic. You can't see which wire is positive and which is negative.

18. ### WBahn Moderator

Mar 31, 2012
18,079
4,917
1) Use a multimeter to check which wire is connected to which terminal.
2) Feel the connector and you should be able to feel which wire is going where.
3) Look up the part number on the manufacturer's website.
4) Guess that the convention that red is positive and black is negative is being used.
5) Make a simple circuit and use one of the connector wires as a conductor in the circuit by breaking one of the wires and tying the red wire to one of the broken ends and then see which terminal you have to touch to the other broken end to get the circuit to work again. Hint: The red wire is connected to that terminal.

absf likes this.
19. ### RdAdr Thread Starter Member

May 19, 2013
214
1
Yes, the easiest way is to check for continuity using a multimeter. I will buy a multimeter in the near future.