Students learn to use infrared (IR) transmitters and receivers that can turn on a circuit from a distance. Then they explore the properties of these devices. What will turn on the receiver besides the transmitter? What else will detect IR light, besides the receiver? What kinds of materials will let IR light pass through, what will reflect it? Will it be focused by a lens? What is the range of the transmitter -- in other words, how close does it have to be to the receiver -- and how can we extend this distance?
Make a chart labeled Communication System Examples, with headings "System," "Transmitter," "Receiver" and "Signal."
Bring in a TV, DVD or stereo remote; and a conventional flashlight (if available);
Photocopy worksheet and assessement (downloadable at bottom of page).
TV, DVD or stereo remote
conventional flashlight (with incandescent bulb)
three coin batteries,one IR transmitter, one IR receiver and one red LED
rubber bands, paper fasteners, cardstock, hook-up wire, strippers, tape
straws, aluminum foil, hand lenses or cups with water, rulers
1. Communication systems: Lead a discussion about what a communication system does. Ask students for examples of communication systems they are familiar with, and lost these on the chart paper. For each one, they should name the system, identify the transmitter and the receiver, and the kind of signal it uses to send information from the transmitter to the receiver. (Click here for more info).
2. Remote controllers: Using the previous discussion as a springboard, ask:
How does a remote controller communicate with a TV set or DVD player?
Students may be surprised to learn that a remote controller uses infrared light to send signals to the TV or DVD player. Help them recall from Lesson 8 that infrared light -- abbreviated IR -- is a form of light that we cannot see, but that has effects that we can see. Ask if they would enjoy making their own remote controllers.
a) How can you tell if the transmitter is on? Look closely at the transmitter when it is on. Can you see a faint red light? Point it towards a cell phone camera. What happens? Why do you think a cell phone can "see" it better than you can? (For more info, click here)
b) Other sources of infrared light: Find other ways to turn the receiver on, besides the IR transmitter. Try sunlight, an ordinary flashlight, an incandescent bulb, an electric space heater or a TV or DVD remote. How can the receiver detect infrared light even though it is black? (For more info click here.)
c) Turning on a buzzer: Replace the red, yellow, green or blue LED with a buzzer. How can you use the transmitter to turn the buzzer on from a distance? (See a video and diagrams).
d) Obstacles: Set up the transmitter and receiver so both are on, and then put your hand between the receiver and transmitter. What happens? Why? What kinds of things will block IR light? What kinds of materials will let it pass through? (For more info, click here).
e) Mirrors: Can an ordinary mirror reflect IR light? Set up a transmitter and receiver so the light from the transmitter has to bounce off a mirror to get to the receiver. How well does it work? Experiment with different surfaces to see which ones reflect IR light, and which ones don't. (For more info, click here).
f) The range of the transmitter: Set up the transmitter and reciever so both are on, and then gradually move the transmitter away from the receiver. What happens? Why? What could you do to keep the receiver on when the transmitter is further away? (For more info, click here).
g) The angle between the transmitter and receiver: To make the receiver turn on, it is best if the transmitter is aimed directly at it, so the IR light stirkes it "head on." But what happens if the angle between them is not exactly right? how much can you rotate the transmitter, and still let the receiver "see" the light? What can you do to improve the reception so the angle doesn't matter so much? (For more info, click here).
This troubleshooting guide covers problems with the basic transmitter-receiver pair. The strategy is to first isolate the problem to the transmitter circuit or the receiver citcuit, and then fix the circuit that is at fault.