Practical Electronics for Inventors
Paul Scherz and Simon Monk
Last Update: 2017-11-15
Five Sentence Abstract:
The book is divided into three parts - theory, basic components, and circuits/modules. While it won't give you the tools to be an electrical engineer, it is more than relevant enough to give you all the basic understanding to build projects with arbitrary complexity - provided you can use this information as the foundation when exploring more complex applications. After the basic components are covered, there are several easy to understand sections on op amps, filters, oscillators, and other non-primitive but foundational aspects of electronics. Some of the more advanced topics that are covered include voltage regulators and power supplies. The book culminates with a look at the, from the inventors standpoint, obsolescent logic gates and their modern successor the micro controller and its digital world before rounding out with motors/servos and audio electronics, often depicted as being controlled by a micro controller.
More than a solid introduction. The book is divided into basically three
sections. The first covers electricity and the physics and mathematics behind
things like capacitance and induction. The next section builds on this theory
by introducing the primitive components first and building on them further to
introduce things like sensors and filters culminating with micro controllers.
The last section deals with digital electronics and the micro controller.
The theory section, while not as detailed as a university electrical
engineering course, is more than enough for an enthusiast to gain foundational
knowledge of the concepts they will be utilizing without necessarily
understanding the ins and outs of things like Kirchhoff's Laws.
Each of the primitive components is given a treatment before moving onto
semiconductors, including a brief description of the doping process and n- p-
These foundations are then expanded to cover, from a working standpoint instead
of the previous sections theoretical view, basic sensors, operational
amplifiers, filters, oscillators, timers, voltage regulators, and power
With these building blocks the book continues by introducing digital
electronics with a cursory treatment of logic gates, which for the casual
builder are all but obsolete. Their successor, the micro controller, is covered
The final few chapters look at motors, servo, and audio electronics.
Lastly the modular electronics chapter discusses how you should generally, at
least as a hobbyist and during the prototyping phase take advantage of modules
and integrated circuits in much the same way that you would use micro
controllers rather than build logic circuits from scratch. For example, unless
you are building an H-bridge as a learning exercise, you are probably better
off buying a module or integrated circuit H-bridge.
Table of Contents
Chapter 1: Introduction to Electronics
Chapter 2: Theory
Chapter 3: Basic Electronic Circuit Components
Chapter 4: Semiconductors
Chapter 5: Optoelectronics
Chapter 6: Sensors
Chapter 7: Hands-on Electronics
Chapter 8: Operational Amplifiers
Chapter 9: Filters
Chapter 10: Oscillators and Timers
Chapter 11: Voltage Regulators and Power Supplies
Chapter 12: Digital Electronics
Chapter 13: Microcontrollers
Chapter 14: Motors
Chapter 15: Audio
Chapter 16: Modular Electronics
- // All page numbers based on epub.
Besides the intrinsic elemental semiconductors, such as silicon and
germanium, there are hybrid compounds—compounds such as gallium arsenide. Other
semiconductors are made by introducing impurities into a silicon lattice. For
example, an atom in the chemical group of phosphorous, arsenic, and antimony
can replace one of the silicon atoms in a lattice without affecting the lattice
itself too much. However, each of these impurities has one more electron in its
valence level than the silicon atom has; this extra electron, for which there
is no room in the valence band, takes a place in the conduction band and can
conduct electricity. A semiconductor with impurities of this sort is called an
n-type semiconductor, and the extra electrons
are called donor electrons.
Atoms of elements in the same chemical group as boron, aluminum, and gallium
have one less valence electron than silicon has. If an atom is added to a
lattice of silicon as an impurity, there is one less electron than is needed to
form a bond that holds the lattice together. This electron must be provided by
the electrons of the valence band of the lattice material, and holes are
created in this band. These holes act as positive charge carriers. The impurity
atoms are called acceptors. A semiconductor with such impurities is called a
- The 10 Percent Rule: This rule is a standard
method for selecting R1 and R2 that takes into account the load and minimizes
unnecessary power losses in the divider. The first thing you do is select R2 so
that I2 is 10 percent of the desired load current. This resistance and current
are called the bleeder resistance and bleeder current.
- From the equation, you can see that when R_load is
very large compared to r_s , (1000 times greater or more), the effect of r_s is
so small that it may be ignored. However, when R load is small or closer to r_s
in size, you must take r_s into account when doing your calculations and
designing circuits. See the graph in Fig. 2.52. In general, the source
resistance for DC power supplies is usually small; however, it can be as high
as 600Ω in some cases. For this reason, it's important to always adjust the power supply voltage with the load connected. In
addition, it is a good idea to recheck the power supply voltage as you add or
remove components to or from a circuit.
- Superposition theorem: The current in a branch
of a linear circuit is equal to the sum of the
currents produced by each source, with the other sources set equal to zero.
- ...RMS or root mean square value, which is found by squaring the
instantaneous values of the ac voltage or current, then calculating their mean
(i.e., their average), and finally taking the square root of this—which gives
the effective value of the ac voltage or current. These effective, or RMS, values don't average out to zero and are essentially the
ac equivalents of dc voltages and currents.
- In the United States, three wires run from the pole transformers (or
underground or surface enclosed transformer) to the main service panel at one’s
home. One wire is the A-phase wire (usually black in color), another is the
B-phase wire (usually black in color), and the third is the neutral wire (white
in color). Figure 2.90 shows where these three wires originate from the pole
transformer. The voltage between the A-phase and the B-phase wires, or the
hot-to-hot voltage, is 240 V, while the voltage between the neutral wire and
either the A-phase or the B-phase wire, or the neutral-to-hot voltage, is 120
V. (These voltages are nominal and may vary from region to region, say 117 V
instead of 120 V.)
At the home, the three wires from the pole/green box transformer are connected
through a wattmeter and then enter a main service panel that is grounded to a
long copper rod driven into the ground or to the steel in a home’s foundation.
The Aphase and B-phase wires that enter the main panel are connected through a
main disconnect breaker, while the neutral wire is connected to a terminal
referred to as the neutral bar or neutral bus. A ground bar also may be present
within the main service panel. The ground bar is connected to the grounding rod
or to the foundation’s steel supports. Within the main service panel, the
neutral bar and the ground bar are connected together (they act as one).
However, within subpanels (service panels that get their power from the main
service panel but which are located some distance from the main service panel),
the neutral and ground bars are not joined together. Instead, the subpanel’s
ground bar receives a ground wire from the main services panel. Often the
metal conduit that is used to transport the wires from the main service panel
to the subpanel is used as the ground wire. However, for certain critical
applications (e.g., computer and life-support systems), the ground wire
probably will be included within the conduit. Also, if a subpanel is not
located in the same building as the main panel, a new ground rod typically is
used to ground the subpanel. Note that different regions within the United
States may use different wiring protocols. Therefore, do not assume that what I
am telling you is standard practice where you live. Contact your local
electrical inspector. Within the main service panel, there are typically two
bus bars into which circuit breaker modules are inserted. One of these bus bars
is connected to the A-phase wire; the other bus bar is connected to the B-phase
wire. To power a group of 120-V loads (e.g., upstairs lights and 120-V
outlets), you throw the main breaker to the off position and then insert a
single-pole breaker into one of the bus bars. (You can choose either the
A-phase bus bar or the B-phase bus bar. The choice of which bus bar you use
becomes important only when it comes to balancing the overall load more on that
in a moment.) Next, you take a 120-V three-wire cable and connect the cable’s
black (hot) wire to the breaker, connect the cable’s white (neutral) wire to
the neutral bar, and connect the cable’s ground wire (green or bare) to the
ground bar. You then run the cable to where the 120-V loads are located,
connect the hot and neutral wires across the load, and fasten the ground wire
to the case of the load (typically a ground screw is supplied on an outlet
mounting or light figure for this purpose). To power other 120-V loads that use
their own breakers, you basically do the same thing you did in the last setup.
However, to maximize the capacity of the main panel (or subpanel) to supply as
much current as possible without overloading the main circuit breaker in the
process, it is important to balance the total load current connected to the
A-phase breakers with the total load current connected to the B-phase breakers.
This is referred to as “balancing the load.” Now, if you want to supply power
to 240-V appliances (ovens, washers, etc.), you insert a double-pole breaker
between the A-phase and B-phase bus bars in the main (or subpanel). Next, you
take a 240-V three-wire cable and attach one of its hot wires to the A-phase
terminal of the breaker and attach its other hot wire to the B phase terminal
of the breaker. The ground wire (green or bare) is connected to the ground bar.
You then run the cable to where the 240-V loads are located and attachthe wires
to the corresponding terminals of the load (typically within a 240-V outlet).
Also, 120-V/240-V appliances are wired in a similar manner, except you use a
four-wire cable that contains an additional neutral (white) wire that is joined
at the neutral bar within the main panel (or subpanel).
- An inductor acts like a time-varying current-sensitive resistance. It only
“resists” during changes in current; otherwise (under steady-state dc
conditions), it passes current as if it were a wire. When the applied voltage
increases, it acts like a time dependent resistor whose resistance is greatest
during times of rapid increase in current. On the other hand, when the applied
voltage decreases, the inductor acts like a time-dependent voltage source (or
negative resistance) attempting to keep current flowing.
- resonant frequency f0 = 1/(2pisqrt(LC))
- Note that we got the phase angle by assuming that the arc tangent of anything
divided by 0 is 90°.
- Note that we got the phase angle by assuming that the negative arc tangent of
anything over zero is −90°.
- As a general rule of thumb, in terms of transmitting a signal, the input
impedance of a device should be greater than the output impedance of the
circuit supplying the signal to the input. Generally, the value should be 10
times as great to ensure that the input will not overload the source of the
signal and reduce the strength by a substantial amount.
- the output impedance of a circuit is simply its Thevenin equivalent
Here are some important things to notice during a forced response in regard
to resistors, capacitors, and inductors:
Resistor: Under a forced response, a voltage is instantly placed across a
resistor and a current immediately flows. There is no delay in voltage or
current response (ideally).
Capacitor: Under a forced response, the voltage across a capacitor cannot
change instantly, so at the instant a transition occurs it acts like an open
circuit or constant voltage source. The voltage at instant t=0− or t=0+
is a constant—the voltage that was present before the event. Also, at the
instant t=0− or t=0+ the current is zero, since no time transpires for
charge to accumulate. However, after t=0+ , the capacitor voltage and
current have a natural response that is a function of time.
Inductor: Under a forced response, an inductor voltage cannot change
instantaneously, so it acts like a short, meaning there is no voltage across it
at t=0− or t=0+ . The current, however, at t=0− or t=0+ will be a
constant—the value of the current prior to the transient event. However, after
t=0+ , the inductor voltage and current have a natural response that is a
function of time.
- Nonperiodic voltages and currents can also be represented as a superposition
of sine waves as with the Fourier series. However, instead of a summation over
a set of discrete, harmonically related frequencies, the waveforms have a
continuous spectrum of frequencies. It is possible to think of a nonperiodic
function as a periodic function with an infinite period.
- a capacitor placed in parallel with a signal path (i.e., to ground) has an
effect opposite that of the coupling capacitor. Instead, it acts as a decoupling capacitor, allowing dc to continue along
the path, while diverting high-frequency signal components to ground—the
capacitor acts as a low-impedance path to ground. A similar effect, known as
bypassing, is used when a capacitor is placed across a particular circuit
element to divert unwanted frequencies around it. Decoupling and bypassing
become fundamental when removing unwanted random high-frequency ripple and
other undesired alterations within a supply voltage (or voltage-critical
location) caused by random noise, or sudden current demands generated by
accompanying circuit elements. Without decoupling and bypassing, many sensitive
circuits, especially those incorporating digital logic ICs, have a tendency to
- [capacitor] For use with other ac signals, the peak
value of ac voltage should not exceed the dc working voltage, unless otherwise
specified in component ratings. In other words, the RMS value of ac should be
0.707 times the DCWV [DC Working Voltage] value or
- JFET followers are often used as input stages to amplifiers, test
instruments, or other equipment that is connected to sources with high source
- A slotted coupler/interrupter is a device that contains an open slot between
the source and sensor through which a blocker can be placed to interrupt light
signals (see Fig. 5.30b). These devices are frequently used for object
detection, bounce-freeswitching, and vibration detection. A reflective pair is
another kind of optoisolator configuration that uses a source to emit light and
a sensor to detect that light once it has reflected off an object. Reflective
pairs are used as object detectors, reflectance monitors, tachometers, and
movement detectors (see Fig. 5.30c).
- The most commonly used metals for a thermocouple are the alloys chromel (90
percent nickel and 10 percent chromium) and alumel (95 percent nickel, 2
percent manganese, 2 percent aluminum, and 1 percent silicon). A thermocouple
made with these materials will typically be able to measure temperatures over
the range -200°C to +1350°C. The sensitivity is 41 μV / °C for these metals.
Rule 1: For an ideal op amp, the open-loop voltage gain is infinite (A_o =
∞). For a real op amp, the gain is a finite value, typically between 10^4 to
Rule 2: For an ideal op amp, the input impedance is infinite (R in = ∞). For
a real op amp, the input impedance is finite, typically between 10^6 (e.g.,
typical bipolar op amp) to 10^12 Ω (e.g., typical JFET op amp). The output
impedance for an ideal op amp is zero (R out = 0). For a real op amp, R out is
typically between 10 to 1000 Ω.
Rule 3: The input terminals of an ideal op amp draw no current. Practically
speaking, this is true for a real op amp as well—the actual amount of input
current is usually (but not always) insignificantly small, typically within the
picoamps (e.g., typical JFET op amp) to nanoamps (e.g., typical bipolar op amp)
Rule 4: Whenever an op amp senses a voltage difference between its inverting
and noninverting inputs, it responds by feeding back as much current/voltage
through the feedback network as is necessary to keep this difference equal
to zero (V_+ − V_− = 0). This rule only applies for negative feedback.
Passive filters are designed using passive elements (e.g., resistors,
capacitors, and inductors) and are most responsive to frequencies between
around 100 Hz and 300 MHz.
Active filters are capable of handling very low frequency signals
(approaching 0 Hz), and they can provide voltage gain if needed (unlike passive
Above around 100 kHz or so, active filters can become unreliable (a result of
the op amp’s bandwidth and slew-rate requirements).
At radiofrequencies, it is best to use a passive filter.
When describing how a filter behaves, a response curve is used, which is
simply an attenuation (Vout/Vin ) versus frequency graph (see Fig. 9.2). As you
discovered in Chap. 2, attenuation is often expressed in decibels (dB), while
frequency may be expressed in either angular form ω (expressed in rad/s) or
conventional form f (expressed in Hz). The two forms are related by ω = 2πf.
Other VCOs (voltage controlled oscillators), such as the 8038 and the XR2206,
can create a trio of output waveforms, including a sine wave (approximation of
one, at any rate), a square wave, and triangular wave.
A popular RC-type circuit used to generate low-distortion sinusoidal waves at
low to moderate frequencies is the Wien-bridge oscillator.
When it comes to generating high-frequency sinusoidal waves, commonly used in
radiofrequency applications, the most common approach is to use an LC
can reach frequencies up to around 500 MHz. However, it is important to note
that at low frequencies (e.g., audio range), LC oscillators become highly
There are a number of ICs available that can make designing crystal
oscillators a breeze. Some of these ICs, such as the 74S124 TTL VCO (squarewave
generator), can be programmed by an external crystal to output a waveform whose
frequency is determined by the crystal’s resonant frequency. The MC12060 VCO,
unlike the 74S124, outputs a pair of sine waves.
In Chap. 13, we will also see how a microcontroller can be used to generate a
waveform using a digital-to-analog convertor. The basic technique is to store
the waveform in memory and then play it through the digital-to-analog
converter. In the case where just a squarewave is required, a simple 8-pin
microcontroller with a built-in clock can be an effective alternative to a 555
timer, requiring fewer external components.
- Note: DSP is a complex area, and there are many good books devoted to this
topic. Understanding Digital Signal Processing by Richard G. Lyons (Pearson,
1996) is one such book.
- When it comes to identifying the characteristics of an unknown stepper, the
following suggestions should help. The vast majority of the steppers on the
market today are unipolar, bipolar, or universal types. Based on this, you can
guess that if your stepper has four leads, it is most likely a bipolar stepper.
If the stepper has five leads, then the motor is most likely a unipolar with
common center taps. If the stepper has six leads, it is probably a unipolar
with separate center taps. A motor with eight leads would most likely be a
universal stepper. (If you think your motor might be a variable-reluctance
stepper, try spinning the shaft. If the shaft spins freely, the motor is most
likely a variable-reluctance stepper. A coglike resistance indicates that the
stepper is a permanent-magnet type.) Once you have determined what kind of
stepper you have, the next step is to determine which leads are which. A simple
way to figure this out is to test the resistance between various leads with an
ohmmeter. Decoding the leads of a bipolar stepper is easy. Simply use an
ohmmeter to determine which wire pair yields a low resistance value. A low
resistance indicates that the two wires are ends of the same winding. If the
two wires are not part of the same winding, the resistance will be infinite. A
universal stepper can be decoded using a similar approach. Decoding a six-wire
unipolar stepper requires isolating two three-wire pairs. From there, you
figure out which wire is the common center tap by noticing which measured pair
among the isolated three wires gives a unit R worth of resistance and which
pair gives a unit of 2R worth of resistance (see Fig. 14.14). Now, decoding a
five-wire unipolar (with common center tap) is a bit more tricky than the
others because of the common, but hidden, center tap. To help decode this
stepper, you can use the diagram and table shown in Fig. 14.14. (The dots
within the table represent where the ohmmeter’s two probes are placed within
the diagram.) With the table you isolate e (common tap wire) by noting when the
ohmmeter gives a resistance of R units. Next, you determine which of the two
wires in your hand is actually e by testing one of the two with the rest of the
wires. If you always get R, then you are holding e, but if you get 2R, you are
not holding e. Once the e wire is determined, any more ohmmeter deducing does
not work—at least in theory—because you will always get 2R. The best bet now is
to connect the motor to the driver circuitry and see if the stepper steps. If
it does not step, fiddle around with the wires until it does.