Figure: LED Connected to Battery with Protecting Resistor.
| Connection | Current | Voltage | Diode | |
| LED | Resistor | Protoboard | Battery |
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A light-emitting diode, or LED, is a diode that emits light when current passes through it in the forward direction. Because an LED is a diode, it passes current only in one direction.
If you connect an LED on its own to your battery, the battery will heat up the LED and destroy the LED. Try connecting one LED to the battery alone by plugging it right across the battery voltage. If you connect it one way, nothing happens, because the LED won't let electrons through that way. Connect it the other way around. Now it should shine and get warm. The correct way is with the long lead on the Positive Terminal and the short lead on the Negative Terminal. The LEDs will not explode. Throw away the LEDs afterwards.
To protect the LED, you need to slow down the electrons coming out of the battery. Use a resistor. The resistors are the small yellow things with stripes on them. Use one with brown, black, red stripes. Look at the diagram below. It is a simple schematic diagram of an electronic circuit consisting of an LED and a resistor.
The schematic shows electrical power coming from two voltages named +9V and 0V. You get these from the positive and negative terminals of a 9-V battery. Connect one end of the resistor to the battery Positive Terminal. Connect the long lead on the LED to the other end of the resistor. Connect the short lead to the Negative Terminal. The LED should shine. Try some other LEDs and see which one you like best.
See if you can get several LEDs to turn on at the same time.
Use the switch to turn on the LEDs, as shown below.
Build the flasher circuit shown below.
Here is a photograph of this circuit, build on a protoboard.
Change the capacitor values to change the rate at which the LEDs flash.
A connectio is a wire between two electronic parts. Another way of defining a connection is that it is a path between two points in a circuit that presents negligible resistance to the flow of electrons when compared to the resistance offered by the remaining parts of the circuit.
Electric current is the flow of electrons down a wire. It is measured in Amps. The current is proportional to the number of electrons that pass through a cross-section of the wire every second.
Electric voltage is electronis bunched up in a wire, wanting to go somewhere where the electronis are not so bunched up. We make electrons go through our circuits on their way to the uncrowded place. On their way, they will do things for us, like making light. The units of voltage are Volts.
A diode is an electronic component with two wires that lets electric current go only one way through it.
The letters LED stand for Light Emitting Diode. Ann LED is a diode that makes light when electric current goes through it. You have a blue box with electronic parts in it. The LEDs are the plastic see-through parts. Some are red, some are green, and some are clear.
A resistor is an electronic component that slows down electrons as they try to go from one place, where there are too many electrons, to another place, where there are too few electrons. We measure resistance in units of Ohms, for which we use the symbol Ω.
A protoboard is a base upon which to build electronic circuits quickly using through-hole components. A protoboard has many holes in it, as you can see here. You plug wires and parts into the holes. Underneath the holes are metal clips that you cannot see. The metal clips connect some holes together, but not others. In the picture, there are columns of five holes and rows of five holes, each marked at either end by a space with no hole. The holes in any column or row of five holes are connected together. Each column of holes is connected to the column above and below it. The columns make two separate strips of holes running up and down the protoboard. You use these to distribute the battery connections to the circuit. Each row of five holes is connected only to itself − unless you connect two of them deliberately with a wire, as we have done in one place in the picture.
A battery is something that pushes electrons out of one lead and sucks them in at another lead. The red wire coming from your batter is the Positive Terminal, or +9 V (plus nine volts). The black wire is the Negative Terminal, or 0 V (zero volts).