The following is the work of Ivan Thorson. Ivar
Thorsons Electronic Crash Course
The Fundamentals and Ohmís
Current is the number of electrons flowing through something.
Current is usually measured in Amperes (or amps). One amp is defined as
one coulomb (6,280,000,000,000,000,000 electrons!) of electrons
flowing per second. If you want to use the water analogy, think of this as
the volume of water flowing through a pipe.
Voltage is the difference in electrical potential between two
points. Positive voltage is usually defined as the absence of electrons;
negative voltages have an excess of electrons. Ground is defined as
totally neutral, with an even amount of protons and electrons. Think of
voltage as the amount of pressure the water in the pipe is under. Another
analogy might be to think of a rock. (Before you start laughing at the
rock bit, let me continue!:-) The rockís voltage is its height relative to
Ďgroundí level, which is where it would normally rest. If, for example,
you lifted the rock above the ground, it would have a positive electrical
potential equal to its height; conversely, if you dug a hole and put the
rock in it, the rock would have negative potential relative to Ďgroundí.
This is a very loose description, but may help you understand it
Resistance is measured in Ohms. At a given voltage, the
resistance determines the amount of current that can flow, according to
Ohmís law. Think of resistance as the size of the pipe the water is
flowing through. The larger the pipe (Lower resistance), the more water
(current) can flow through.
IMPORTANT: Voltage and resistance determine how much current will flow.
Current and resistance do NOT determine the voltage. In electronics-speak,
"the voltage leads the current".
Ohms law is:
I = E/R
I = Current in amps.
E = Voltage in Volts.
Resistance in Ohms.
So, to show a relevant example, letís pretend that I have a 9 volt
battery, and I want to use it to power a solarengine instead of a solar
cell (maybe I broke all my solar cells, as I sometimes do). Grabbing a
resistor that I have lying around, I read the color coding (more on that
later), and find that it is a 2.2K Ohm resistor (2200 Ohms). Plugging
these two variables into the formula, I get:
I = E/R
I = (9)/(2200)
I = 0.00409 amps
0.00409 amps rounds to 0.0041 amps, or 4.1 mA. This should be more than
enough to power your average solarengine, unless itís very inefficient or
was made incorrectly.
Remember, you can still work backwards with this formula. For example,
if you needed 10 mA (0.01 Amps) to power something, such as a coil with a
resistance of 1000 Ohms, you get:
I = E/R
0.01 = E / (1000)
E = 10 Volts
By the way, itís the current that will kill you. High voltages are
dangerous because your even though your body has a fairly high resistance
(varies from 100K Ohms or less to several Megs), a high voltage allows
more current to be passed through your body.
Resistors are arguably the most commonly used
components in all of electronics. A picture of a few different resistors
is shown in Figure 1. Without resistors, circuits would fry, there would
be no analog electronics, yada yada, life would be bad for electronics in
Resistors come in a few different wattage ratings; common power ratings
are 1/8, 1/4, 1/2, 1, and 2 watts. If a circuit doesn't specify which
wattage rating to use, I generally use 1/4 watt carbon film resistors.
Larger watt resistors are physically larger and able to dissipate more
Resistor color code
There are two kinds of resistor color coding, the four-band system and
the five-band system. In the four-band system the first two color bands
are the first and second digits of the resistance, the third is the
multiplier, and the fourth digit is the tolerance. Example:
The first two digits are 1 and 0, which
gives us 10.
Green is 5, so we add 5 zeros (or multiply by
10*100,000 = 1,000,000 Ohms (1Meg)
First two digits are 2 and 2, which gives us
Multiplier is 2 zeros (100).
22*100 = 2200 Ohms (2.2K)
How do you tell which band is the first band? It's the one closest to
the edge of the resistor. The 'last' band should be somewhere near the
center of the resistor.
In the five-band resistor system, the first three bands are the
first three digits, and the fourth and fifth bands are the multiplier and
tolerance, respectively. Since this allows you to be more precise (three
significant digits), the five band system is generally on precision
A resistor with a tolerance of 10% means that it will vary plus or
minus ten percent of it's rated value. A 300 Ohm resistor with a 10%
tolerance will vary 30 Ohms either way, meaning its actual resistance is
between 270 and 330 Ohms. The most common tolerance is 5%, and there is
usually no need for a smaller tolerance unless the circuit demands it.
Potentiometers, or pots, are very useful when dealing with analog
electronics. They are essentially a long resistor hooked up to a 'wiper'
that slides along the resistor, which provides adjustable resistance. Pots
are sometimes called trim pots when used to 'trim' a circuit so that it
runs straight. This is often literally true when dealing with microcore
walkers; once trimmed, they walk considerably straighter.
I was going to have pictures of the different sizes and shapes of pots,
but my scanner just broke. So I'll describe them. Cylinders with shafts
sticking out, little boxes with a flathead screw on one side, or oblong
shapes with other methods of adjustments. All potentiometers have three
terminals and a shaft or screw head that can be turned to change the
Pots have three terminals, which makes them very versatile. The pot has
a fixed resistance between the outside two terminals(we'll say 1 meg, for
this example), and the center terminal sort of slides (or rotates) back
and forth along the resistor. When the pot's shaft is turned all the way
clockwise or counterclockwise, there is 1 meg of resistance between the
center terminal and (for example) the left terminal. Between the right
terminal and the center terminal, there is now (ideally) no resistance.
Turning the shaft all the way the other direction should reverse the
situation, and there should be 1 meg of resistance between the center
terminal and the right terminal. Turning the shaft somewhere in between
gives some ratio in between, for example 600K of resistance from the
center terminal to one terminal, and 400K to the other terminal. The
resistance between the center terminals and the outside terminals must
always equal the resistance between the outside two terminals
There are two main kinds of pots: linear taper and logrimithic or
exponential taper. Linear taper means that turning the wiper alters the
resistance by a linear amount (ie. one hundred ohms per degree).
Logrithimic or exponential taper means that turning the first degree may
vary the resistance by a 4 ohms, the second degree is 9 ohms, the third
degree is 16 ohms, etc. This sort of exponential taper is common when used
with sound systems, as sound does not get 'louder' at a linear rate.
Capacitors are like miniature batteries, to horribly simplify it.
They store small electrical charges, can discharge them rapidly, and are
very frequently used in electronics. However, they are far more efficient
than batteries, but have a fraction of the energy storing ability.
Capacitors are often referred to as caps, since people get sick of writing
out the word Ďcapacitorí.
Capacitors are measured in Farads. One Farad is equal to one Coulomb of
charge at one Volt of potential. Again, one amp is equal to Coulomb of
electrons per second. One Farad of
capacitance is a huge amount, and can usually
only be found in expensive gold foil capacitors, such as the large black
one shown at left.
Capacitors come in two general flavors, polarized and non-polarized.
Polarized capacitors have a positive and negative terminal, and you had
better pay attention that you stick it in the circuit right, because
certain capacitors can explode when connected backwards at their rated
There are many different kinds of capacitors (Figure three shows a few
kinds), all of which have different tolerances (this is just like a
resistor's tolerances, but I will explain it again). A tantalum capacitor
may have a rating of +/- 20%. This means that value of a 10uF (0.00000001
Farad) capacitor may actually have a capacitance of 8 to 12 uF, depending
on the temperature of the capacitor. Donít worry, this should affect your
circuits little unless it is sensitive. Ceramic capacitors are often the
worst; they usually have a +60% / -40% rating, so a cap rated 10uF may
actually be between 6 and 16 uF! I prefer using +/-5% capacitors, but
thatís a personal preference. Many circuits use ceramic capacitors with no
trouble at all. When building microcores, it is generally wise to stay
away from caps with ratings worse than +/- 20%.
Other commonly known types of capacitors are polyester, electrolytic,
polypropylene, stacked metallized film, gold foil, and others.
Safety note: Donít play with high voltage or super large
capacitance capacitors, such as the ones out of camera flashes. They can
be very dangerous! Though it may only have a few mF of capacitance, it is
at a very high voltage and is designed to discharge very rapidly! Always
discharge a capacitor before touching it by using a resistor (Use ohm's
law to figure out how larger, generally bigger than 2K is fine for most
voltages) to short out the two terminals in the capacitor. Hold it there
for 30 seconds to assure that it is discharged. I once touched my thumb to
a camera flash capacitor that I assumed was discharged and I received a
nasty shock, and assumed I had discharged it entirely. WRONG! I got
shocked 2 times more, though not as badly as the first...
Parallel and series
Figure 4 is the standard parallel circuit using resistors as an
example. The resistors could be replaced with, capacitors, diodes, solar
cells, and other components and it would still be a parallel circuit.
Figure 5 is the standard series circuits using resistors.
Figure 6 is a series-parallel circuit, named so because it is a
combination of a series and parallel circuit. Makes sense, doesn't
The math of series and parallel
For resistors, the formula for resistors in series is:
RTotal = R1 + R2 + R3 + ... +Rn
Simple, huh? Just add all the values together. For resistors in
parallel it gets more difficult.
RTotal = 1 / [(1/ R1) + (1/ R2) + (1/ R3) + ... + (1/ Rn)]
And for calculating series parallel circuits (fig 3), you just
calculate the parallel portion of the circuit first (usually), and then
take the equivalent resistance of the parallel circuit and substitute that
into the series circuit equation. Then repeat those two steps again, if
need be. Just use your math and logic skills; youíll be fine.
Finding the capacitance and voltage ratings of capacitors in series and
parallel is simple as well. For finding the equivalent voltage of
capacitors in series, just add the voltage ratings of all of the
capacitors together. For finding the voltage rating of capacitors in
series, you just take the value of the capacitor with the lowest voltage
rating, as common sense suggests.
Finding the combined capacitance of capacitors in parallel with one
another is easy too; add the capacitance of all the capacitors together.
However, finding the capacitance of capacitors in series, you must use a
more complicated formula:
CTotal = 1 / [(1/ C1) + (1/ C2) + (1/ C3) + ... + (1/ Cn)]
Note that this is the same as the formula for resistors in
parallel. For other components, (solar cells, coils, etc.) you can
generally just guess which of the formulas to use, based on what you know
about the component. Putting three solar cells in parallel will triple the
current, putting them in series will triple the voltage. Simple, eh? Well,
not quite, as a three identical solar cells in series will produce triple
the voltage, and put out the same amount of current as one of the single
solar cells. Above all, use common sense.
...and no, this doesnít mean Radio Controlled...:->
RC circuits, or Resistive-Capacitive circuits are used very often in
electronics as well as in BEAM (take a close look at the microcore).
Capacitors charge exponentially when powered through a resistor.
This means that the voltage doesnít rise at a regular rate. Figure 7 shows
a chart of a capacitor charging over time. Why does the graph look like
this? Well, at each time constant (which really isnít a true constant,
youíll see why) the cap charges to 63% of the difference between the capís
voltage and the source voltage. What does that mean? Well, hereís an
Youíre charging a capacitor with a 10 V battery. So, starting with a
dead capacitor, the charge cycle goes as follows.
1 6.3V (10V - 0.0V = 10. volts difference. 63% of
10.V is 6.3V So, 0.0V + 6.3V = 6.3V)
2 8.6V (10V - 6.3V = 3.7
volts difference. 63% of 3.7V is 2.3V So, 6.3V + 2.3V = 8.6V)
9.5V (10V - 8.6V = 1.4 volts difference. 63% of 1.4V is 0.9V So, 8.6V +
0.9V = 9.5V)
4 9.8V (10V - 9.1V = 0.5 volts difference. 63% of
0.5V is 0.3V So, 9.5V + 0.3V = 9.8V)
5 9.92V (10V - 9.1V = 0.2
volts difference. 63% of 0.2V is 0.12V So, 9.8V + 0.12V =
If you didnít catch all that simple (and mildly rounded) math back
there, then all that you really have to know is that after 5 time
constants, a capacitor is considered charged for all intents and purposes.
Mathematically, the capacitor will continue to charge closer and closer to
the source voltage forever, but that doesnít happen in real life, since
capacitors leak and are imperfect. So, now that you know how a capacitor
charges, how do you find the time constant?
T = RC
Simple, eh? So a 1 mega ohm resistor charging a one uF capacitor the
time constant would be:
T = (1,000,000)(0.000,001)
T = 1 second
Brilliant! From this we can find that it would take roughly 5 seconds
for the capacitor to reach the source voltage.
If you didnít understand all of this, consider the water analogy again.
We know that the resistance of a circuit is equivalent to the size of a
pipe, generally speaking. A capacitor is kind of like a big water tank. As
the water pours in from the pipe, it begins to fill up the tank. However
there is "air" in the tank that keeps the water from coming in at a
constant rate. The air compresses as the water comes in, causing the water
to come in more and more slowly until the water has filled up the tank and
compressed the air into an infinitely small space. When that has happened,
the capacitor is charged. Generally speaking, though, after 5 time
constants it's considered charged (99% worth, at least).
Diodes and transistors are generally comprised of two types of silicon;
for lack of a better name, weíll call them type P and type N silicon, and
let's not go into molecular details, this is a crash course, after
all....P means that it is positively charged, N is negatively charged.
When combined together, these two types of silicon make diodes,
transistors, and all that nifty stuff that allows computers to
work...Transistors are also a whole lot smaller and cheaper than their
predecessor...the vacuum tube.
Diodes have a single junction, which is where the P silicon and N
silicon touch. When the P silicon is connected to a positive voltage
greater than what is called a threshold voltage (0.7 for silicon, 0.3 for
germanium), the diode conducts almost like a closed switch and is
called forward biased. If you connect the P silicon to a negative
voltage, then it is considered reverse biased and will not conduct
electricity. The P silicon in a diode is called the Anode, the N silicon
is the Cathode.
I don't have any pictures of diodes handy at the moment, but they are
similar in shape to resistors. Cylindrical shaped, with two leads sticking
out each end (Radial). However, diodes are smaller, lots of different
colors, and have no markings except for possible black band denoting the
Transistor theory can get fairly complex, but since you most
likely aren't reading this to get your degree as an electronics engineer,
here's the short version...
Bipolar transistors come in a variety of packages and types. They are
called Bipolar because they have two junctions, and can be divided into
two types: PNP and NPN. NPN means that it has two negative silicon plates
sandwiching a positive silicon plate. They can almost be thought of as two
diodes that were squished with the P or N sides together.
Almost every transistor has three pins(Unless you broke off a pin, or
it has four!); a collector, base, and emitter. The emitter pin is
designated by a small arrow pointing in (towards the center of the circle)
or out (away from the center). The easy way to remember if a transistor is
a PNP or an NPN by looking at a schematic is to see if the arrow is
pointing in or out. It's a NPN if the arrow is "Not Pointing
iN", and a PNP if the arrow is "Pointing In
Point. (I know it's fairly redundant, but it works for me!)
Transistors can act like amplifiers or switches. They have something
called gain (or beta) which is a term to describe the ratio of increase in
current, voltage, or both of the transistor. A transistor with a gain of
150 (typical for small transistors, for power transistors it's more like
30 to 70) can amplify a signal coming to the base about 150 times before
it reaches the collector.
As for the actual transistor operation, it's magic until you read a
book about it. Which I recommend you do.
Integrated circuits (or IC's) are those funny little black boxes
with little metal pins sticking out of them (figure 3838). The ones that
are rectangular shaped and have pins on opposite sides are called DIPs
(Dual Inline Pins). SIP (Single Inline Pins) IC's are less common, but do
Examples of DIP IC's are the 74ALS245, 74C14, 7404, and all those other
cryptic part numbers that you will gradually pick up. You will learn to
love IC's, as they will save you a lot of time since they contain tiny
circuits that will prevent you from having to solder together lots of
transistors and resistors to get a digital logic gate. What's that? See
Digital Logic Gates
Digital logic gates are generally 2-state devices (Off/On, Low/High,
0/1. All the same, just named different.) Here are the main variety of
gates and their truth tables:
(A and B are inputs, OUT is, well... the output! 1 is HIGH or close
to positive source, 0 is low or close to ground/negative source)
YES (Buffer or Amplifier)
...man it's a pain working with tables by hand...need an
By looking at the tables, it's easy to find out what gate you need for
different applications. See below for info on what they look like.
The Binary System
It may help you to know the binary system. Generally you use
hexadecimal (or hex for short) with small microcontrollers, so here are
the first 16 numbers in decimal (base 10), hexadecimal (base 16) and
binary (Base 2).
Notice that it takes four bits (each 0 or 1) to describe a single digit
in Hex. Four bits is called a nibble, and 8 bit word is a byte.
Other things to Know
Voltage ratings: Voltage ratings are the maximum voltage that
can be safely applied to a component. This doesn't mean you have to run it
at that rating, though! I have often used a 63V capacitor for a 3V
application and it works fine. A 10 or even 6 volt rated cap would have
been preferable, but wasn't available to me at the time. Besides, a lower
rated voltage cap will be smaller for it's capacitance.
Static discharge: This usually isn't an issue in BEAM robotics.
Watch out for MOS (Metal Oxide Semiconductor), they fry easily. Also, any
Pentiums or Pentium II's are also easily fryable...If it worries you,
ground yourself (touch metal or dig deep hole and stick arm in it...)
before working with the parts. Wrist bands are available that will
automatically keep you grounded, as well.
AC current: Alternating current. Power is
transmitted to your house via AC, because it loses less energy in the
transmission.Current flows two ways. See figure 10 for a picture of
different AC waveforms, as is the last of which is used in your household
AC. If you have taken Algebra II and know about the unit circle,
learning about AC power will be considerably easier. I am not going to
explain it in detail, as it has little to to with BEAM robotics. If you
want to know more, buy a book at the top of this page. I love saying that.
It makes it not my problem any more! ;-)
DC current: Direct current. Think batteries and the like.
Current flows one way.
Filter caps and Rectification: Filter caps and diodes are used
to take an AC waveform and convert it into DC current. How's it do that?
Well, figure 11 shows us all we need to know. Figure 11-A shows the
standard sine wave of an AC circuit, 11-B shows it after it's been half
wave rectified by using diodes in the pattern used in figure 11-C. 11-D
shows what happens when a large enough capacitor is placed between
positive and ground, and acts as a filter capacitor. This is greatly
exaggerated, as good filter capacitors and voltage regulators can make the
ripple virtually nonexistent. This process is basically what happens in
your household AC adapters used for CD players and other systems. However,
they also use transformers to step down the voltage.
Transformers: Transformers have to main coils, a primary coil
and a secondary coil. The primary coil is attached to the AC source
voltage, and the secondary coil(s) will step up or step down the voltage
according to the number of turns it has relative to the primary coil. If
the primary coil has a 100 turns, and the secondary has 200, it will
double the voltage and halve the current. So a 1 amp of current at 10
volts flowing through the primary coil would yield us 20 volts at 0.5 amps
at the secondary coil. Transformers lose energy in the transfer, however,
and only work with AC current.
Zener Diodes: Zener diodes act like normal diodes, except their
forward voltage threshold is built to be many times higher, for example
3.3 volts or more. Up until their forward threshold voltage, they act like
a reverse-biased diode.
LEDís: Green, red, yellow, or blue Light Emitting Diodes
that emit light when powered. They act like normal diodes, can be
reverse-biased and forward-biased. However, it is not usually safe to use
these in place of diodes, as LED's, unlike diodes, consume current. If put
in a high current circuit, they will sometimes explode or melt. Use a
resistor (Usually 1K or more) in series with the diode to prevent it from
using more than a few milliamps of current.
FLED's : Flashing Light Emitting Diodes. They have a
built in circuit that flashes the LED on and off. Their forward threshold
voltage is around 2.3 volts., making them useful for solarengines.
Photoresistors: Resistors that change their resistance in
different light levels. Great for making walkers phototropic.
Phototransistors: Transistors that change their gain in
different light levels.
Photodiodes: Diodes that both emit a small current and have
their forward threshold voltage change in response to different light
3-State logic: High, low, and a high impedance state. Basically,
this allows a computer or logic circuit to output a 1, a 0, or switch to a
high impedance (almost like high resistance, see below)state where it
doesn't affect the circuit it's connected to.
Impedance: Impedance is defined in Ohms, just as resistance is,
but describes the "total" opposition to AC current flow, taking into
account both resistive and reactive (like a capacitor) components into
Wires and copper traces: Those copper lines on the bottoms of
circuit boards. They conduct electricity from component to component.) are
assumed to have no resistance, so as not to affect the operation of the
rest of the circuit. In real life, there is some resistance, but it can
usually be ignored unless it is a very sensitive circuit. A larger wire
will have less resistance then a small one; there's more metal for the
electricity to flow through. Same goes for traces on the bottoms of copper
Reading a schematic
Reading a schematic isn't tough, just takes practice and a little
thought. Here's a diagram with all of the commonly used electronics
symbols on it...Keep in mind that these symbols may differ from schematic
to schematic in some slight ways. For example, the resistor may have two
or three little zigzags. Good circuit diagrams will also explain what
obscure components are, anyway.
Switches : N.O. and N.C. stand for normally
open and normally closed. SPST=Single Pole Single Throw. SPDT (Single
Pole, Double Throw). Not shown is the DPDT (Double Pole, Double Throw)
which is basically two SPDT's.
Transistors : To find out which pin is
emitter and which is collector (Base is always the center pin), check the
data sheets of the transistor (usually in the catalog that you ordered the
transistor from). Most 2NXXXX and 39XXseries general purpose transistors
have a pin out of (from left to right, looking at the flat face of the
transistor with the pins pointing down) Emitter, Base Collector.
Methods of building a
Freeform : Shown at left, this is a fairly
difficult way of assembling a circuit, as there are many opportunities for
mistakes. It's also not as strong as other methods of construction.
However, it is the smallest and lightest way of soldering a circuit
together, making it great for small solarollers, photovores and the like.
The circuit shown at left is a half finished microcore. It works, but
If you decide to go with free form, STICK TO THE SCHEMATIC! Otherwise,
you will get very confused and solder it together incorrectly.
Solderless Breadboard : Shown at left, you can
see the wires connected to one of my walkers. The basic concept is that
you use single strand wire of 22 or 24 gauge single strand copper wire (or
around there) to connect the circuit by plugging the wire and components
in the solderless breadboard. The inside the little holes that you stick
the wire in are little copper terminals that connect the holes together in
groups of five, with long bus lines for power, ground, or whatever you
want to connect a lot of leads to..
Breadboard/Protoboard : They are
wired up the same as the solderless breadboard, except that they are made
up of fiberglass with copper traces on one side and holes drilled every
10th of an inch in a grid. Stick the leads through the holes, and solder
them in place. No picture, I'm out of film.
PCB : A lot of work. It's usually not worth designing
one for just one robot. PCB's are those green things that you see
everywhere inside of electronics. Homemade ones are usually yellowish, but
no less effective.
AUTHOR: Ivar Thorson
I will take it from here
This is an awesome book by Paul Horowitz and Winfield Hill.
Just get it. It costs Rs.300($6) in Moore market whereas you might
have to pay Rs.375 in a branded book store like Higginbotham's. Awesome
pricing because its a Cambridge low price edition.
These are the links to some good basic electronic tutorials.
Don't forget to come back!
A guide to soldering
A guide to desoldering
guide to making PCB's
Ben Hitchcock's INFO - A basic electronics guide