We will be constructing a simple LED circuit. This guide is directed towards absolute beginners in hobbyist electronics. Nothing is assumed about prior knowledge; explanation and clear instruction is provided so the beginner may know what he or she is doing as the circuit is being constructed.

Step 1: Materials & Prerequisite Knowledge

First gather the following materials:

Breadboard
Two jumper wires
One 1.8k ohm resistor
One LED
One 9v battery & battery clip

These materials are readily available from any electronics store: perhaps from the aging Radioshack or anything like it. Any basic electronics kit will have, except the battery, all the components.

A 1.8k ohm resistor is used for this task because it is the resistor I had on hand. Do not (read: absolutely do not) use a resistor with an ohm rating less than 330 ohms. This surpasses the common LED threshold of 3V across the LED @ 20 milliamps which will overload the LED. Anything over 330 ohms is fine, but going too high may not cause the LED to illuminate.

The breadboard is the base from which we will build the circuit; it will conduct the electricity and allow the other components listed above to be connected in a circuit. The breadboard looks as above; it is not a board on which to cut bread. It is instead a plastic board with conducting rails inside of it, with slots where we may insert the component 'leads.'

I have above painted the conducting rails over a picture of the bread board. Notice current is only conducted along the rows, and then is not conducted between the halves of the board. This means, if a complete circuit is constructed, the leads of some components must be in the same row as some other components.

It is not important to absolutely understand this, but the knowing so is useful in diagnosing problems which may arise while constructing the circuit.

Step 2: Connecting the Battery Clip

Often breadboards have power rails down one side or both sides. These rails are where the battery is typically connected, so the battery leads are not directly inserted into the middle of the circuit; power rails allow for a neater management of cables.

The red wire of the battery clip should be inserted into any slot of the red power rail, often labeled '+,' since the positive lead of the battery is often connected here. Insert the black lead of the clip into the blue line labeled '-.' If you have not guessed why, it is because the '-' line is intended to receive the negative lead of the battery clip.

Step 3: Attaching the Resistor

The resistor, which often looks like a little drum with two steel leads, may be inserted into two slots which are not horizontal. This is so the leads are not connected; think of the leads like inputs and outputs of a machine. It would make no sense to connect the input to the output!

Resistors are indifferent to which direction current flows through them; they only function to hinder current flow by a little. The quantity in ohms associated with each resistor is helpful in interpreting how much the current is hindered; a 1.8k ohm resistor inhibts current much more than a 100 ohm resistor (note: 1.8k ohms simply means 1800 ohms.)

The resistor value can be determined simply by the color bands on the resistor. I have included a handy piece of paper which I use to help make sense of these bands.

Often it is helpful to follow the pictures I have provided if you are just beginning, as any easy-to-make mistake may deform the circuit so it does not light the LED.

Step 4: Attaching the LED

The LED (often) looks like a small bulb with two steel leads coming from it. The LED I am using has been retired (ungracefully) from an old computer, so your LED will most probably look different. LEDs do care which side accepts the current and which side outputs the current (that is to say the LED is 'polar.') Often, and especially with unsnipped leads, the longest lead of the LED is positive. Otherwise a flat side on the bulb of the LED may indicate the negative side of the LED.

The positive lead of the LED must be placed in the same row as one of the two resistor leads. This ensures the charges will flow from the resistor into the LED. The resistor is placed in the circuit so electricity does not flow fast enough to burst the LED. The resistor may have been placed anywhere within the circuit but this configuration is only a preference.

Step 5: Connecting the Jumper Wires

Now we will introduce the power rails into the circuit. Because the power rails are not connected to the body of the breadboard, current cannot normally flow between the two. This is why jumper wires are required. They may be any kind of conducting wire with the exposed leads. Conveniently my breadboard came with many jumper wires and so I will use those, but scrap copper wire may be used in place.

Connect one lead of the first jumper in the same row as the resistor lead which is not connected to the LED and connect the other lead to the '+' column of the power rails. Insert, then, one lead of the second jumper wire into a slot within the same row as the LED lead which is not connected to the resistor, then connect the other end into the '-' column of the power rails.

The jumper wires are connected where they are because we want current to flow into our little system from one side and then come out the other side. If it were to exit in the middle, for instance where the LED and resistor connect, the LED would not be in out circuit!

Step 6: Connecting the Battery

The battery will drive this circuit, and is necessary for its operation. The battery contains a potential difference which we will harness to illuminate the LED.

Connect the battery to the battery clip. There is only one way it will snap on, so do not worry about attaching it backwards.

Step 7: Checking the Circuit

I have include a little diagram of the flow of current from the battery through the circuit.

Note: This is not the way the electrons flow. Electrons actually flow opposite the way we think of current as flowing. Current flow is just useful to electricians, as it was the way charge was originally thought to travel; do not worry too much about this.

If your LED does not illuminate, do not worry, you may have attached the LED backwards. Simply swap which of the leads is in which slot. If that does not remedy the problem, study the pictures I have included and the circuit is complete (that is, charge is able to flow from the battery through the circuit and back into the battery without being interrupted.

There are many more areas of hobbyist electronics to explore; I would encourage you to discover these areas, as the pursuit of these are very fun, and rewarding in their challenge.

Introduction: Simple LED Circuit