Activity 3: Opto Transmitter Time Required: 45 minutes Materials List Group Size: 2 Each pair needs: One each of: One Activity 3 bag containing: o 4.7 kω Resistor (Yellow, Violet, Red) o 1 kω Resistor (Brown, Black, Red) o 100 Ω Resistor (Brown, Black, Brown) o 0.1 μf Disc Capacitor (Labeled 104) o 0.01 μf Disc Capacitor (Labeled 103) o IR LED These items are provided in a separate bag, but will be placed back in Activity 3 bag after activity for use in subsequent years: o 50 kω Potentiometer (variable resistor) o 555 Timer IC o Seven 2 Jumper Wires 9 V Battery Battery Snap (in bag with breadboard) Breadboard To share between every two groups: Tape measure Multimeter Pliers Student Handouts Activity 3: Opto Transmitter Learning Objectives After this activity, students should be able to: Identify and use a potentiometer. Identify and use a 555 Timer IC. Transmit an audio tone from an opto transmitter to an opto receiver. Introduction Last time we met, you built an infrared receiver similar to the one in a TV or DVD player. This time, you will build a basic transmitter that will transmit a series of tones to the infrared receiver using an infrared (IR) light emitting diode (LED). The IR LED is similar to the red and blue LEDs you used in the first activity, except the IR light is invisible. The circuit will use a 555 timer integrated circuit to pulse the LED on and off to transmit the signal. This is similar to the transmitter in a TV remote which transmits a specific Pilot Module Spring 2008 (Updated 2/7/08) 23
signal for each button on the remote. You will test these transmitter circuits using the receiver circuits built in Activity 2. Vocabulary Word Potentiometer Infrared (IR) Opto Transmitter IR LED Integrated Circuit (IC) Definition Variable resistor. Invisible light. Circuit that sends out light signals. Infrared Light Emitting Diode. This is a device that converts electrical energy into infrared light. A small, solid device with many electronic components inside. Procedure Instructor Preparation: (Time = 10 minutes) Check each multimeter and 9 V battery by turning the knob of the multimeter to the 20 V DC setting and touching the probes to the battery terminals. The multimeter should read more than 8.7 V. If the multimeter reads less than 8.7 V, try a second meter. If that still reads less than 8.7 V, try a new battery. During the Activity: 1) Split students into groups of two. 2) Let the students know that there are many small parts in these kits. They should be careful while using them not to lose any. While working on this project, the students should work with their partner while not disturbing other groups. Students should also be warned to be careful not to disturb the components of other groups. Do not knock another group s table. 3) Pass out electronic components. Tell the students not to connect the battery to anything until they are told to do so! 4) Walk around and help the students as they work through the activity. a. The batteries should be connected to the opto receiver and the opto transmitter ONLY when the circuits are ready to be tested. b. If the opto receiver does not produce sound when the opto transmitter is fired at the phototransistor in the receiver, have the students move the IR LED in the transmitter directly up against the phototransistor in the opto receiver. c. It is a good idea to retest the opto receiver by firing the TV remote at it. d. If the student is still unable to get an output from the opto receiver, have him/her remove one of the battery leads from both of their breadboards and follow the trouble shooting procedure in the student handout. Pilot Module Spring 2008 (Updated 2/7/08) 24
e. If the battery leads are hard to get into the breadboards, try twisting the strands of the wires to form a firmer end of the wire. 5) At the end of the activity, ask the students to put the components back in their original bags. 6) Collect the components from the students. The batteries go back in the boxes to keep the contacts from touch something metal and short circuiting. Processing and Activity Closure: Now that you ve finished building your opto transmitters what do they sound like when you fire them at the receiver circuit? What happens when you rotate the stem on the potentiometer? [Allow the students to talk about what they have learned. They will likely note that the transmitter doesn t transmit nearly as far as the remote control. They only transmit a few inches while the remote transmits across the room. If they don t, ask them the following.] How far did your opto transmitters transmit? How far did the remote control transmit last week? [Use the remote control to show them this.] Why do you think the remote control can transmit so much farther? [Let them think about this question and encourage them to make some guesses.] There are two main reasons why the remote control might transmit farther: 1) The invisible light from the infrared LED can be made brighter to transmit farther. It is just like a light and the light in the transmitter might be dimmer than the light in the remote. 2) The invisible light from the IR LED in the remote is focused so that it is all going in one direction. This is just like using mirrors or a magnifying glass to point visible light in one direction. Many light fixtures use a reflective material behind the light to focus light down into a room. The light from the IR LED in the remote is focused in a similar manner. We can t see these differences because the light is invisible, but this is how the signal can be made to travel a longer distance. Can an IR LED transmitter, like the remote control or your opto transmitter, transmit a signal through a solid object that you can t see through? [Answer: No] Why not? [Answer: If you can t see through the object, the infrared light will be blocked by the object and none of it will get to the receiver.] Next time, we will build a similar circuit that will transmit sound. The sound signal will come from a portable music player. If you have a portable music player that you can plug headphones into, please bring it next time. This could be a portable radio, mp3 player, portable CD like a discman, or a portable tape player. Pilot Module Spring 2008 (Updated 2/7/08) 25
Additional Resources Chaney Electronics BBK-3 44 in 1 Communications and Opto Lab Kit http://www.kitsuse.net For more information about 555 timer ICs: http://www.williamson-labs.com/480_555.htm For more information about how speakers work: http://electronics.howstuffworks.com/speaker.htm Assessment 1) Collect or copy page 27 of the student handout. The question, Can you give two examples of where you would find a dial that can be rotated to control electricity? will be used to assess whether or not students can identify places where a potentiometer could be used in an electrical device. Many of the controls they identify will not in fact utilize a potentiometer, but the important aspect is that for these rotating dials, a potentiometer could be used in that device. 2) On a separate sheet of paper, please indicate what percentage of the students were able to use the measuring tape to measure the distance the transmitter was able to transmit without help. During activity 2, the students were introduced to a measuring tape for measuring the distance the remote control could reach. In this activity, we will test their ability to use the measuring tape. If the students need help with the tape, you should help them. You should not tell them that you are keeping track of which teams are able to do it without help. They do not need to know this. References Chaney Electronics, 44 in 1 Communications and Opto Lab Manual, 1997. Authors: Dr. Gary A. Ybarra, Dr. Paul A. Klenk Contributors: No additional contributors Copyright: Engineering K-Ph.D. Program, Pratt School of Engineering, Duke University Pilot Module Spring 2008 (Updated 2/7/08) 26
Activity 3: Opto Transmitter Student Handout Name: Date: In this activity you will build an opto (optical) transmitter that uses a 555 timer IC to pulse an infrared (IR) light emitting diode (LED). You will use this circuit to transmit different tones to your opto receiver built in Activity 2. The first thing to do is to identify the parts you will need. Parts List R1: 4.7 kω Resistor (Yellow, Violet, Red) R2: 1 kω Resistor (Brown, Black, Red) R3: 100 Ω Resistor (Brown, Black, Brown) P1: 50 kω Potentiometer (variable resistor) C1: 0.1 μf Disc Capacitor (Labeled 104) C2: 0.01 μf Disc Capacitor (Labeled 103) L1: IR LED IC1: 555 Timer IC 9 V Battery Battery Snap Breadboard 2 Jumper Wires Tape Measure You know how to identify the resistors from Activity 1 by using the resistor color code. The 50 kω potentiometer (variable resistor), or pot, has a rotatable stem and three leads. Rotating the stem changes the resistance between the center lead and the leads on the outside. Pick up a pot and rotate the stem clockwise and counterclockwise. Write down three examples of where you might find a pot. make sound louder or quieter. A potentiometer allows you to rotate a dial to control the electricity through it. For example, a volume control allows you to rotate a dial to Can you give two examples of where you would find a dial that can be rotated to control electricity? Example 1: Example 2: Pilot Module Spring 2008 (Updated 2/7/08) 27
The disc capacitors are brown and are not polarized. It does not matter which way you plug in these capacitors to your breadboard. They are labeled 103 and 104 as follows: 0.1 μf Disc Capacitor (Labeled 104) 0.01 μf Disc Capacitor (Labeled 103) The 555 IC looks just like a 386 IC (but says 555 on it instead of 386!). It has 8 pins. If you orient the IC with the notch to the left, the pin numbers are counted going counterclockwise around the IC beginning at the lower left. The infrared (IR) LED has a smoky clear body as shown in the picture to the left. One lead is longer than the other. The longer lead is positive (+) and the shorter lead is negative (-), just like a visible light LED. Pilot Module Spring 2008 (Updated 2/7/08) 28
Overview The opto transmitter circuit you will build has the following schematic. The numbers shown inside the rectangle representing IC1 indicate the 555 timer pin numbers. For example, pins 4 and 8 of the IC are connected to the +9 V power supply rail and pin 1 is connected to the negative power rail. The black dots emphasize that a physical connection is made. For example, the black dot at the end of the wire from pin 2 of the IC indicates that the wire is connected to pin 6 as well as C1 and R2. As you build the circuit on your breadboard, you should look back at this schematic frequently to relate the schematic drawing to your breadboard circuit. Pilot Module Spring 2008 (Updated 2/7/08) 29
When you have built the entire circuit, it should look like the picture to the left. Generate an outline of the process you would go through to build this circuit. Compare the picture of the circuit to the left to the schematic on the previous page. In general, the last element to be connected in any circuit is the battery. We will leave the battery connection until the very end of the building process. A good place to start building any circuit that contains an IC is with the placement of the IC onto the breadboard. Then, the other elements can be placed around the IC. Building the Opto Transmitter Circuit The first component to place on your breadboard is the 555 Timer IC. With the notched end of the IC toward the top of your breadboard, gently insert the IC into the breadboard with pins 4 and 5 in row 10. Using 2 jumper wires, connect pin 1 of the IC to ground (negative power rail) and pin 8 to the +9 V power rail. We also need to connect pin 4 to the +9 V power rail. You could connect a jumper wire all the way from pin 4 to the +9 V power rail OR you could connect a jumper from pin 4 to pin 8! These connections provide power to the 555 Timer IC. Pilot Module Spring 2008 (Updated 2/7/08) 30
Connect C1 (0.1 μf labeled 104) between pin 2 of the IC and ground (negative power supply rail). Connect C2 (0.01 μf labeled 103) between pin 5 of the IC and hole E12. Then connect a jumper wire from hole A12 to ground. This effectively connects C2 from pin 5 to ground. Connect a jumper wire from pin 2 of the IC to pin 6. This jumper will criss-cross over the top of the jumper wire that connects pins 4 and 8. Connect R1 (4.7 kω yellow, violet, red) between pin 7 of the IC and the +9 V power supply rail. Connect the IR LED with the positive + (longer) lead in hole F1 and the negative (shorter) lead in hole E1. Bend the IR LED so that it is pointing along the surface of the table. Connect R3 (100 Ω brown, black, brown) between pin 3 of the IC and hole C1. Connect R2 (1 kω brown, black, red) between pin 6 of the IC and hole G16. Connect a wire jumper from pin 7 of the IC to hole F18. These connections are for the pot. Pilot Module Spring 2008 (Updated 2/7/08) 31
Position the pot so that the stem is pointing toward you with the left lead in hole J20 as shown in the picture to the left. The middle lead will be inserted in hole J18 and the right lead will be inserted in hole J16. Gently push the pot into the breadboard until the pot is fully seated as shown in the picture to the left. Finally, connect a 9 V battery to a battery snap and connect the battery to the power supply rails. The circuit should now be operating. To test the circuit, aim the IR LED at the photo-transistor of the opto receiver that you built in the last activity. Position the opto transmitter so that the IR LED is 0.5 inches away from the phototransistor of the opto receiver. You should hear a tone. As you twist the stem of the pot, the frequency of the tone should change. If you do not hear any sound out of the speaker, you will need to troubleshoot your opto transmitter circuit. Pilot Module Spring 2008 (Updated 2/7/08) 32
If your circuit does not work, immediately disconnect one of the battery snap leads from the breadboard. Troubleshooting (Go through this process if your circuit fails to operate) Troubleshooting is the process of figuring out why a circuit does not work. 1) The most common problem is a wiring error. Check to make sure that every wire and component lead is going into the hole you think it should go into. 2) The second most common error is a polarity mistake. Check the polarity of the IR LED. 3) Is the battery dead? Use the voltmeter to measure the voltage across the battery terminals. Is it 9 V or higher? If not, replace the battery. 4) If all else fails, replace the 555 Timer IC. The problem with the circuit must be one of the mistakes listed above. You must go through each step carefully until you find and correct the problem. Exploration Turn the stem of the potentiometer and listen carefully to the sound that is produced by the speaker. Write down below what the sound sounds like as you twist the pot stem. The sound produced in the opto receiver sounds like As I twist the pot stem, the sound What is the maximum distance you can separate the IR LED from the phototransistor and still get sound? Answer: Pilot Module Spring 2008 (Updated 2/7/08) 33
Disassembling the Opto Transmitter Circuit You will store your opto receiver for use in Activity 4. You will disassemble your opto transmitter. Remove the potentiometer, resistors, jumper wires, capacitors and IR LED. Care must be taken when removing an IC from the breadboard. The easiest way to do this is to use a pair of needle nose pliers to extract the IC as shown in the figure below. Grip the IC on the ends with the needle nose pliers. Do not squeeze the pliers too tightly, as this can damage the IC. Hold the breadboard down with your other hand. Carefully pull the IC direct out of the breadboard. The idea is to avoid bending the pins of the IC. Return the circuit components to their proper storage bags as instructed. All of your small components from the breadboard will go in the Activity 3 bag except the battery snap. The battery snap and breadboard will go in a bag together. Finally, return the battery to your instructor. Pilot Module Spring 2008 (Updated 2/7/08) 34