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Wireless Transmission: Your TV Remote 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 k Resistor (Yellow, Violet, Red) R2: 1 k Resistor (Brown, Black, Red) R3: 100 Resistor (Brown, Black, Brown) P1: 50 k Potentiometer (variable resistor) C1: 0.1 F Disc Capacitor (Labeled 104) C2: 0.01 F 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 k 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. 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 make sound louder or quieter. 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 2/13/08) 27 Wireless Transmission: Your TV Remote 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 F Disc Capacitor (Labeled 104) 0.01 F 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 2/13/08) 28 Wireless Transmission: Your TV Remote 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 2/13/08) 29 Wireless Transmission: Your TV Remote 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 2/13/08) 30 Wireless Transmission: Your TV Remote Connect C1 (0.1 F labeled 104) between pin 2 of the IC and ground (negative power supply rail). Connect C2 (0.01 F 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 kyellow, 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 brown, black, brown) between pin 3 of the IC and hole C1. Connect a jumper wire from hole J1 to the +9V power supply rail. Connect R2 (1 k 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 2/13/08) 31 Wireless Transmission: Your TV Remote 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 2/13/08) 32 Wireless Transmission: Your TV Remote 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 2/13/08) 33 Wireless Transmission: Your TV Remote 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 2/13/08) 34