Lab4_2C_2009

Lab4_2C_2009 - ECE 2C Laboratory Manual 4 Infrared PWM...

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1 © Bob York ECE 2C Laboratory Manual 4 Infrared PWM Transmitter Overview In this lab you will construct a circuit to produce a 40kHz analog pulse-width-modulator (PWM), to be used later in our one-way analog audio communication link. Later we will combine this modulator with the microphone circuit from am earlier lab to form a complete IR audio transmitter. In the following lab session we will build the IR receiver circuit to complete the communication link. The lab will explore: Basics elements of a communication link Analog PWM modulation in particular Some elements of optical signal propagation and detection Limitations on data rate due to circuit components Table of Contents Pre-lab Preparation 2 Full Schematics for IR PWM Modulator 3 Parts List 3 Background: Analog Communication Links 4 Information and Bandwidth 4 Baseband Transmission vs. Modulated Carriers 5 Pulse-Width Modulation (PWM) for Optical Communications 7 In-Lab Procedure 8 4.1 Variable Duty-Cycle Circuit 8 4.2 Analog Pulse-Width Modulation 9 Other PWM Circuits 10 4.3 A Simple Infrared Link 10 Transmitter 10 IR Detectors 11 4.4 Hardwire the Transmitter Circuit 13
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2 Infrared PWM Transmitter © Bob York 2 Pre-lab Preparation You have one week to complete this lab. Read through the lab experiment to familiarize yourself with the components and assembly sequence, and complete the calculations below. Before coming to the lab, each group should obtain a parts kit from the ECE Shop. Bring your solderless breadboard, tools, & wire jumpers. Required calculations: Determine the capacitance C1 in the 555 timer circuit of Fig 1 that is needed to provide pulse frequencies of 4kHz and 40kHz, respectively. 4kHz: C1=______________uF 40kHz: C1=______________uF Coupling capacitor C3 and the resistor chain R1-R2-R6 form a high-pass filter. For the component values shown in the schematic, find the maximum and minimum cutoff frequencies as potentiometer R6 is varied over its full range. min L f = ______________Hz max L f = ______________Hz Determine an appropriate value for the IR LED biasing resistor R9 to provide a 50 mA current flow, assuming a power supply voltage of 12V. The forward voltage drop of the diode can be determined from graphs provided in the data sheet. R9 = ______________ Optional: Simulate the PWM circuit using MultiSim or Circuit Maker™ (circuit files available on the course web site).
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Pre-lab Preparation 3 © Bob York 3 Full Schematics for IR PWM Modulator LM393N Figure 4-1 – Schematic for the Infrared Pulse-Width Modulated Transmitter. Parts List Qty Description Circuit Semiconductors 1 TIMER, LMC555CN (DIP-8) U2 1 COMPARATOR, LM393N (DIP-8) U1 1 Op-Amp, LF353N (DIP-8) U3 1 BJT_NPN, 2N3904 (TO-92) Q2 1 BJT_PNP, 2N3906 (TO-92) Q1 1 IR High Eff. Emitter TSAL6100 (5mm) LED1 1 IR Photodiode, BPV23F (side view) IRD1 1 IR phototransistor (T1 3/4) Q3 Passives E S I S T O R , 1 k 10% 1/4W R11 E S I S T O R , 3 . 3 k 10% 1/4W R1,R2,R7,R11 E S I S T O R , 4 7 k 10% R3, R4, R12 E S I S T O R , 1 0 k 10% 1/4W R5, R10 2 POTENTIOMETER, 10k R6, R8 1 CAPACITOR, 0.001μF 10% (low-volt ceramic) C1 1 CAPACITOR, 0.0022μF 10% (low-volt ceramic) C1 1 CAPACITOR, 0.0047μF 10% (low-volt ceramic)
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This note was uploaded on 12/28/2011 for the course ECE 2C taught by Professor Yue during the Fall '08 term at UCSB.

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Lab4_2C_2009 - ECE 2C Laboratory Manual 4 Infrared PWM...

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