Lab11_Project - LABORATORY EXPERIMENT Infrared...

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LABORATORY EXPERIMENT Infrared Transmitter/Receiver (Note to Teaching Assistant: The week before this experiment is performed, place students into groups of two and assign each group a specific frequency between 5 and 20 kHz so that prelabs can be completed successfully.) In this laboratory, we will combine all the concepts learned this semester in order to design an infrared (IR) transmitter and infrared receiver. You and a fellow classmate will build the transmitter on one of the small protoboards given to you by your instructor, whereas your receiver will be built on the other protoboard given to you by your instructor. Use the ELVIS board to test your circuits. One of the main problems you will encounter is noise, manifested in the form of ambient light. Therefore, we will need to design a circuit that is immune to the effects of ambient light. Furthermore, the circuit must be designed so that it doesn’t interfere with your fellow classmate’s circuit. Please note that this laboratory will involve the use of certain circuit components whose physics and engineering courses will be covered in greater detail in other courses. However, we will provide the necessary knowledge required to complete this project. It is necessary that you read all the background information of this laboratory BEFORE proceding with the experiment. To make the transmitter/receiver circuit immune to noise more immune to noise, the transmitted signal needs “look” different than the noise. This is achieved by modulating the IR LED diode on and off at an appropriate chosen frequency through the use of an astable 555 timer. Then, a receiver will be built that is much more sensitive to this frequency than to other frequencies. A block diagram of the system is provided below in figure 1. Figure 1: Block diagram of the IR transmitter and receiver
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In figure 1, we see that the circuit has been divided into two structures: the transmitter structure and the receiver structure. In the transmitter, we see that when the button is pushed, the astable 555 timer oscillates and causes the IR LED to emit a modulated, or pulsed, infrared signal. This signal is received via our receiver circuit’s phototransistor. The highpass amplifier allows us to preserve only the high frequency components of our received signal. The bandpass filter is tuned to our modulation frequency, thus removing more noise at higher and lower frequencies. The signal at this point is a high frequency AC signal. The rectifier and lowpass filter convert the signal from AC to DC, and the comparator allows us to adjust the sensitivity threshold so that we do not detect spurious noise signals. Finally, the flip-flop toggles the output on and off with each subsequent press of the transmission button. This project can be completed over two laboratory sessions. For the first laboratory
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This note was uploaded on 07/10/2011 for the course EEL 3113c taught by Professor Staff during the Spring '11 term at University of Florida.

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Lab11_Project - LABORATORY EXPERIMENT Infrared...

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