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ECE20B Lab, Winter 2002
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Lab 2 Prelab Assignment (Week 3, January 21 - 25)
Reading Assignment:
Lab Book (Carley and Khosla) Chapter 9 (Speaker Driver),
Rizzoni Chapter 4 about the transistor
Prelab Questions:
1. (5 points) Analyze the gated oscillator circuit shown in Fig. 3.2. Describe the
output for Vin = 0 V, and 5V respectively. What is the function of Tr4? What
is the function of R20? What minimum Vin would you expect to turn the
oscillator on?
Experiment 1: (Exercise 1, chapter 9) Testing the beeper circuit
1) Test the beeper circuit using the function generator. First set up the circuit as
shown in Fig. 3.1 using the protoboard. Use the function generator to generate
a 0 - 5 V square wave with a frequency of 2.5 kHz and verify the waveform
with the oscilloscope. Input the square wave to the beeper circuit (Fig. 3.1).
(The top of the beeper element should have a dot on it or else a "+" on the
bottom next to one of the leads. The lead directly below this dot or next to the
"+" should go to the +5V side) Vary the input frequency from 100 Hz to 5 kHz,
observe and sketch the voltage waveform across the speaker using the
oscilloscope. Describe the tone you hear. What are the maximum and minimum
frequencies you can hear?
Fig. 3.1 Beeper circuit
Experiment 2: (Exercises 2 - 5, chapter 9) Testing the Gated Oscillator Circuit
2) Build the gated oscillator circuit (shown in Fig. 3.2) on the protoboard. Use the
inverter chip installed on the robot during lab 1 (Chapter 8 of Carley and
Khosla). Remove the chip (4069) using the IC extractor with force applied
ECE20B Lab, Winter 2002
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evenly at both ends. Power the +5V port of the inverter chip using the +20 V
part of the power supply. The transistor TR4 (2SA1015Y) is wired like ECB. If
it is 2SA1015H it is EBC (see Chapter 1 Fig. 1.7).
Observe Vout on the oscilloscope when Vin is 0 V and 5V. Sketch the waveform
in your labbook when Vin = 5V, record the frequency and amplitude. Compare
with Prelab results.
Try different values for R12: 15, 68, 100 k, measure the frequency of Vout on
the oscilloscope. Tabulate frequency versus the product of R12 C9. Determine
the proportionality constant between the two quantities.
Fig. 3.2 Gated Oscillator circuit.
Experiment 3: (Exercises 6-7, chapter 9) Testing the beeper circuit connected to
the oscillator
5) With R12 set at 68 k, connect the Vout of the oscillator to input to the beeper
circuit (Fig. 3.1). Vary Vin slowly from 0 to 5V and back to 0V again. Note the
input voltage at which the beeper begin to sound and the voltage at which it
turns off. Carefully justify the observed voltage values.
6) Assemble the beeper circuit according to the instruction in Exercise 7, chapter
9 of Carley and Khosla.