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by Neil E. Cotter

Associate Professor (Lecturer)

Last Updated: 1/29/12

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LED circuit introduction

Using your kit, build the LED circuit shown in the diagram below. Proceed as follows:

1) Snap the 9 V battery into the batter y clip that snaps onto the terminals of the 9 V battery. The battery and clip are shown at the top of the diagram below.

2) Lay your white, rectangular, plastic breadboard (that has many holes in it) on your desktop with row number 1 at the top, as shown in the diagram below.

3) Poke the black wire (darker wire) from the battery clip into the hole in the upper left-hand corner of the breadboard, as shown in the diagram below, and poke the red wire (lighter wire) from the battery clip into the hole in the upper right-hand corner of the breadboard. Be careful to poke the pins in vertically without bending them. You now have power to the board, with 0V running all the way down the column on the far left side of the board, and +9 V running all the way down the column on the far right side of the board. Note that 9 V is a fairly low voltage, and working with it is no more dangerous than handling a 9 V battery. Also, much of the circuit has insulation on it, preventing contact. As for causing harm to the parts in the circuit because of a wiring error, the battery clip has a protective resistor that limits current and protects components. You may wire without fear!

4) Find one of the four 1 kohm resistors in your bag of components. The resistors have colored stripes on them to indicate their value. Since all four resistors have the same value, you may use any one of them. Bend the leads of the resistor so they are perpendicular to the body of the resistor and plug the resistor leads into the holes as shown in the diagram. The resistor will stand up off the board, which is fine.

5) Find the LED (Light Emitting Diode) in your kit. The LED looks like a small light bulb, and it will light up when the circuit is completed. On the diagram, the LED is shown as a red triangle and flat line inside a circle between rows 17 and 18 on the board. Insert the longer lead of the LED in row 17 and the shorter lead of the LED in row 18. If the leads are the same length, look for a flat side on the plastic edge around the bottom of the LED. The pin next to the flat side goes in row 18. Note: if you insert the LED backwards, it will not light up but will be unharmed. If your LED does not light when you are finished wiring, try turning the LED around.

6) Add the remaining (small) wires shown on the diagram. Use the colors indicated, and carefully insert the wires down into the holes so the wire rests on the surface of the breadboard. You should avoid bending the wires. Note that you will use the small wires from the bag in the kit, not the much longer wires in the kit. When you add the final wire, your LED should light up. If the LED fails to light up, check that every wire and lead is in exactly the right hole. The metal clips inside the breadboard connect certain holes to each other. You must have wires in the correct rows in the middle portion and the correct columns on the sides in order to make a complete circuit.

7) Follow the path that current takes around the circuit as it flows out of the battery through the red wire, through the wires, resistor, and LED, and then back into battery through the black wire. Current must always flow in a circle, hence the name "circuit".

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