Homework 9 - Answers

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Coastal Alabama Community College - Bay Minette *

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101

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Electrical Engineering

Date

Apr 3, 2024

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docx

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1

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PWM Out Low Pass Filter Out Homework Assignment 9 1. Consider a K22 Kinetis chip (K22P144M120 to be more specific…). A datasheet for the chip is available in Canvas. Consult the “Pinout” section (chapter 10). Alice wants to connect the K22 Kinetis to the L3G20DH gyroscope using I2C0 (I2C port 0). She has decided to use pins 81 and 82 (PTB0-PTB1) to do this. Continuing the pinout example, Alice now wants to use FTM1 Channel 0 for PWM. a. Since pins 81 and 82 are now reserved for I2C0, what options does she have? Express your answer in terms of pin number, port, and bit number, like “Pin 95 PTB16”. There are two options. Pin 60 PTA8 and Pin 64 PTA12 b. For each of the two options, which “ALT” column is the FTM1 option found in? ALT3 for both 2. Consult the document in Canvas that explains how to filter PWM to DC, and consider the PWM with a 24 kHz PWM clock. a. For a 1 mV ripple, what is the needed attenuation? 1 mV / 3.3V = 0.000303 b. What is f 3dB ? f3dB = 24kHz * 0.000303= 7.27 Hz c. Using a 10 µF capacitor, what size resistor is needed? R = 1 / (2π*7.27*10µ) = 2188 ohms or larger. For example, you could round up to 2.2k. d. Draw a schematic of the PWM output, resistor, and capacitor, clearly labeling where the low-pass-filtered output comes out. User Interfaces 1. What is considered the simplest user input? Pushbutton 2. Which display technology corresponds to the following: a. Movie theater projector DLP b. Modern big-screen television (identify two) OLED or LCD 3. Why does the “up” elevator button light up immediately when you press it, even though the elevator is usually a few minutes away? Immediate feedback – you know the input was received instantly 4. What aspect of user interface design makes software development difficult? Constant changes in requirements (and also low latency) Retail Technology 5. Why were barcodes invented? Machine readable using inexpensive laser technology 6. Compare magnetic stripe to smart cards: Which is more secure and why? Smart card: data is always encrypted 7. What is considered the least secure form of payment? (Hint: your bank account routing number and account number is printed in plain view.) Writing a check
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