Class Discussion Item "Hints"

for the book:
Introduction to Mechatronics and Measurement Systems
4th edition, McGraw-Hill


1.1     Think about washing machines, dishwashers, microwave ovens, sprinkler systems, and A/C and heating systems.


2.1    When the last connection is made, a spark occurs at the point of connection as the completed circuit is formed.  This spark could ignite gases produced in the battery.  The negative terminal of the battery is connected to the frame of the car, which serves as a ground reference throughout the vehicle.

2.2    The load current will affect the divided voltage.

2.3    Refer to the reasons listed on p. 32.

2.4    Be careful to distinguish between line voltage and voltage drop.

2.5    An electric razor with a DC motor and rectifier circuit may be overloaded.

2.6    A typical household AC circuit in the U.S. is 110 Vrms rated at 20 A. You can find the circuit current ratings on the circuit breakers in your house breaker box.

2.7    A transformer requires a time varying flux.

2.8    Impedance matching.  Also, excessive currents could cause overheating.

2.9    Consider electrical circuits in an automobile, a radio, a house, etc.

2.10    The frame is a conductor.

2.11    The chassis is "hot" and ungrounded.

2.12    The housing is "hot" and ungrounded.

2.13    Excessive ground currents can cause significant voltage variations at different ground points.

2.14    The heart is on the left side of your body.

2.15    Higher points build up more charge.  Close feet minimizes the effects of large ground currents.


3.1    Forward biasing occurs at -0.7 V.

3.2    The switch attempts to change the current instantaneously.  Inductors generate voltage to oppose current changes.  The diode allows the voltage to dissipate through the resistor.

3.3    Forward bias is required for charging. "Leaking" causes voltage decay.

3.4    Current divides between the zener diode and the load.

3.5    Refer to a data book.

3.6    Rectification and regulation is required.

3.7    Vload is limited to the range VL to VH

3.8    When Vg - Vt approaches Vdd, pinch-off occurs and the MOSFET leaves the active region.

3.9    Consider circuits in a computer and in an automobile.


4.1    A violin's waveform is much more complex due to larger harmonic amplitudes.  The guitar "harmonic" technique suppresses the fundamental so the first harmonic (which is twice the frequency or an octave above the fundamental) dominates.  On a piano, harmonics generated by one string excite vibration in strings that naturally vibrate at those frequencies.  For the note C, the harmonics are C (twice the frequency or an octave), G (three times the frequency), etc.

4.2    High frequencies (needed to represent sharp corners) are attenuated.

4.3    Plot the exponentials to see their effect.

4.4    When current flows through a resistor, its temperature and resistance increase.

4.5    There is no g in the equations.

4.6    Settling time is important.

4.7    Vertically oscillate the supported end very slowly, at the natural frequency, and very quickly, and note the respective resulting amplitude and phase response of the suspended mass.  Compare the results to the figures.

4.8    The natural frequencies and damping constants can be used to predict the results.

4.9    A spring is analogous to a capacitor.

4.10    Consider a liquid-in-glass thermometer and a strip-chart recorder.


5.1    If I+ = 0, V+ = 0 regardless of what is between the noninverting input and ground.

5.2    Infinite gain would create an infinite output voltage.

5.3    The string vibrations create the sound from the amplifier which further intensifies the vibration of the strings.

5.4    The integral of a constant is a straight line and the integral of a sine wave is a cosine wave.  Also, think about the effects of the parameters in section 5.14.1.

5.5    Consider a low-pass filter at the input.

5.6    Plot sawtooth and square waves along with their derivatives and integrals.

5.7    Consider the effects of the maximum output voltage swing.

5.8    See Design Example 9.1.


6.1    OCT: octal,   DEC: decimal

6.2    All logic and arithmetic can be performed with binary operations.

6.3    Consider circuits in appliances and automobiles.

6.4    Use a truth table to prove equivalence.

6.5    Include every possible input combination in the diagram.

6.6    Consider the detailed steps required for a read and write operation.

6.7    Include the switch delay and the small NAND gate delays.  Also, see Figure 6.11a.

6.8    All of the J inputs are sampled at each negative edge of the clock signal.  The Q outputs update a fraction of a second after the inputs have already been sampled.

6.9    Consider a digital clock and circuits within a computer.

6.10    Review the differences between BJTs and MOSFETs in Chapter 3.

6.11    Trace through the circuit with each possible input combination.

6.12    Consider a totem pole output sinking or sourcing current and an open collector output sinking current.

6.13    Consider what happens as R1 is decreased.

6.14    Refer to the data book.

6.15    Any input pulses occurring during Δt are lost.

6.16    The counter outputs may not all change at the exact same instant.

6.17    Switching can causes small current and voltage spikes.


7.1    Consider ignition control, emissions control, anti-lock braking, environmental control, audio equipment, cruise control, air bag system, etc.

7.2    Consider when the second LED is turned on.  Is it ever turned off?

7.3    Is the counting handled the same way?

7.4    Use assignment statements and mathematical expressions.

7.5    Can the wire-ANDing be extended to more than two switches?

7.6    Consider chip count, amount of knowledge required, and implementation time.

7.7    Consider step response of an RC circuit (first order system) and the use of a single pin as an output and then an input.

7.8    See the documentation for the BUTTON statement and consider the use of pauses to let switch bounce settle.

7.9    Consider the approximate total execution time based on a 4 MHz clock speed.

7.10    RA4 is an open-drain output.


8.1    The wheel may appear to be turning slower or faster, or it may even appear to not be turning.

8.2    See Equation 8.1.

8.3    Twelve-bit resolution over a typical voltage range (e.g., +/- 10 V) usually provides enough accuracy.  Calculate the quantization size for a +/- 10 V range.

8.4    Consider cost and possible reasons to discretize.

8.5    See what changes are required in the paragraph before Equation 8.8.

8.6    A laser can detect the presence (1) or absence (0) of small pits in the surface.  Audio CD technology uses a sampling rate of 44 kHz.  Assume 16 bits per sample.

8.7    Components required include: A/D, FFT, fundamental detector, and code generator.


9.1    Interrupt (break) a simple unswitched light circuit, creating two unconnected wires.  Connect each wire to the poles of the switches.  Complete appropriate wiring among the throws of the switches.  Verify that all switch position combinations result in the desired functionality.

9.2    The secondary coil on the side of the core displacement experiences a larger voltage.

9.3    See the paragraph before Class Discussion Item 9.1 and consider the Sampling Theorem.

9.4    For the binary code, consider the transition from 7 to 8.

9.5    Test the equations at several codes.

9.6    Consider the effect on the counter.

9.7    Limit switches and a homing sequence can be used to establish reference positions at start-up.

9.8    See Equations 9.11 and 9.12.

9.9    Consider heating effects.

9.10    See Equation 9.21.  Assume R3=R4.

9.11    A strain gage can add significant stiffness to very thin and/or very flexible parts.

9.12    To achieve a reasonably smooth representation of the variation in strain during the gait, a sampling rate of at least 10X the gait frequency would be required.

9.13    Is the deflection measured from the equilibrium position of the spring?

9.14    Crystal vibrations produce pressure waves (sound) and visa versa.


10.1    Consider latches, locks, speakers, and circuits in appliances.

10.2    The laminations perpendicular to the shaft.

10.3    Look at the polarity of the stator and rotor fields.

10.4    Label the poles and commutator segments and carefully follow the path of the armature wire around the poles between the segments and determine the magnetic north direction for each pole when power and ground are connected to each possible segment combination.

10.5    Review the sum-of-products and product-of-sums methods and Boolean expression simplification in Chapter 6.

10.6    Consider cost, size, and power.

10.7    Consider both small (e.g., electric razor) and large (e.g., large appliance) devices.

10.8    Consider the piston rod.


11.1   Calculate the average of several successive finite-difference calculations to show that it is equivalent to a single finite difference over the entire interval.

11.2    Follow the instructions at the end of the item and include all signals.


C.1    Ductile metals fail in shear.