Simple Circuit - Testing the LEDs
Let's build a very simple electrical circuit and test the LEDs in your kit.
LEDs are like little light bulbs but they have a few special properties that you must watch out for:
- they only let the electricity flow in one direction, not the other,
- they change suddenly from being "off" to being "on" without a gradual transition, and
- if you let too much electricity flow through them, they will get damaged and could even break suddenly, shooting sharp pieces of broken plastic into your eye.
Get out the Arduino, the breadboard, some wires, a resistor and the LEDs. Notice that the LEDs have one wire shorter than the other. To make the electricity flow in the right direction, you must always connect the shorter wire to the negative (or ground GND) side of the circuit. To make the LED turn on, you must complete the circuit by connecting the longer wire to the positive side of the circuit. LEDs usually need a minimum of about 1.5 V to turn on. The Arduino can supply 3.3 V or 5 V which is plenty. ***BUT*** you MUST include a resistor in the circuit to stop the LED from getting too much electricity.
Resistors come in a wide variety of values. Their value, in Ohms, is written in a special colour code on most resistors. For this circuit, we shold use a resistor with a value of a few hundred Ohms: 330 Ohms is good. 330 in colour code is orange-orange-brown, with another gold stripe to show the tolerance of 5%. If you're interested, you could search on-line for the complete resistor color codes.
Connect the parts together as shown in the diagrams below. The first diagram shows a realistic picture of the circuit, the second picture is called a schematic diagram. Compare the two and compare with your own circuit so that you can learn what they mean. When you are pluggin the LEDs into the breadboard, make sure all of the shorter wires go into the line of holes beside the blue line.
Get the teacher to check your circuit.
When the teacher has checked it, he will give you permission to plug in the Arduino so that it can power the circuit. See if one of the LEDs lights up. Move the red wire to connect to the longer wire of each LED in turn. Make sure all you LEDs are working. If they do not turn on, check to make sure you have the long and short wires in the right places.