Tips and Tricks - Adding LEDs (Part 3: Building Circuits)

Circuit Design
So now that you have the tools, and you've selected the appropriate LEDs for your project, it's time to design a circuit. Your basic 1 LED circuit, will look like

That's all there is to it. A voltage source (aka battery), a resistor, and an LED. Now is where the math comes in. What you want to do is solve for the value of the resistor. The equation is:

R = (VS - VL)/I

where R is the value of the resistor, VS is the voltage source, VL is the voltage load from the diode, and I is the current. For example, lets assume you have 3V battery, and an LED which needs 2V and can handle a maximum current of 15 mA. The calculated resistor value is

R = (3 - 2)/0.015 = 66.667 ohms

Since that's not a standard resistor value, select the next highest value, 68 ohms. That's all there is to it. If that's all you need, you can head to the next section on soldering.

If you want a circuit with more LEDs, things get a little more complex. The math isn't really much more challenging, but you need to determine whether or not you want the LEDs in series or in parallel. LEDs connected in series are LEDs that have connected along a single path. LEDs connected in parallel are connected so the same voltage is applied to each component. Examples of each are shown below (series on the left, parallel on the right).

To make life simple, I recommend heading to the LED Wizard. This calculator does all the math for you. In addition, it gives you different design options. Now with a plan in place, it's time to hook everything together.

Soldering
Soldering is a process in which two or more metal items are joined together my melting a filler metal into the joint. It's a pretty simple process, but it takes some getting use to. It's a little hard to understand with just words, so check out the video below for how to do this.

Completed Circuits

Simple Circuit
This is your basic one LED circuit. Below are images of the circuit design and the actual circuit. The red wire will connect to the positive end of the battery and the black wire will connect to the negative end.

Series Circuit
In the images below, you can see what a series circuit looks like. On the left is the design. On the right is the actual circuit. Just like the simple circuit, the red wire will connect to the positive end of the battery and the black wire will connect to the negative end.

Parallel Circuit
Below are images for a parallel circuit. Like before, on the left is the design and on the right is the actual circuit. The red wires are connected together and this combination will connect to the positive end of the battery. Similarly, the black wires are connected together and the combination will connect to the negative end.

Most likely, you will not want the battery to run at all times. The solution to this will be covered in Part 4: Switches.