From Schematic to Reality

Understanding Schematics

Schematics are the lingua franca of electronics. They
provide a concise and comprehensive diagrammatic
description of a circuit. Plus, they are mostly
standardized so once you learn the general idioms of a
schematic, you can decipher almost any schematic.

Schematics are especially important to stompbox
building, because so many schematics are available. Of
course, the most popular designs are represented well
with PCB layouts, perfboard layouts, vero-board, etc.
But if you want to enjoy the true wealth and diversity
of designs, you’ll want to understand how to read
schematics.

This article describes schematics, their symbols,
layout and tips and tricks for reading them. From there,
we’ll work on how to translate schematics into the real
world in the form of things you build on a breadboard,
point-to-point, or some type of perfboard media.

Behold, The Schematic

As a starting point, let’s look at a schematic of a
very simple boost pedal based on the Electro-Harmonix LPB-1.

Figure 1.1: A Schematic

You can see that there are various bits represented
by symbols, all connected in various ways. Let’s look at
some of the big picture concepts:

Left to Right: The first thing to notice is that
you read the schematic left-to-right: the input on
the left feeds the signal through parts and pathways
in the middle to an output on the right. This
left-to-right convention is not universal, but it is
probably the most common layout for a schematic.

Power and Ground: The
top area of the schematic shows some type of power
(in our case, 9 volts Direct Current, the same thing
that comes out of a 9 volt battery). The bottom of
the schematic shows grounds. This directly maps to
the physical arrangement of our power source, again,
a 9 volt battery. The top of the schematic is
showing the positive (+) voltage, and ground
represents the negative (-) side.

Symbols: Components are denoted by a standardized set of
symbols, each representing a specific type of
component. For example: a resistor:

Each symbol shows a part number and a part value
or type. R1 denotes two things. First, the “R”
signifies a resistor. Even though the schematic
symbol itself is unique to a resistor, it is helpful
to denote the part type. This is also a somewhat
standardized format: R for resistor, C for
capacitor, Q for transistor, VR for variable
resistor, etc. The number part is just a sequential
counter that makes it easy to cross reference
against a parts list. The number also makes it
easier to talk about schematics. (It’s a lot easier
to say “change the R1 value to 500K for more bass”
than to say “change the first resistor that is
connected from the input to the ground, before the
first capacitor, for more bass.)

Connections: The connections between components
are shown by lines. That is easy enough—anywhere
there is a line, you are reading that there is a
conductor (a wire or the copper trace on a PCB).
Where the connectors cross over can be kind of
tricky because there is no real standardized way of
showing it. Is it just crossing over with no
connection, or is it connected? The following
diagram shows the three most commonly used
connection representations:

Figure 1.2: Various Ways of Depicting Connected Lines

In the first example on the left, a dot shows
interconnecting lines. So A, B, C and F are all
connected together. Lines that pass over another line
are not connected, so D is only connected to E. In the
second example, dots are not used. Instead, a line that
intersects without the little “hump” pass over, is
connected. So the first and second diagrams are the
same. The third example shows another where the dot
signifies a connection, and non-connected crossing lines
do not use the hump pass over convention.

Inputs and Outputs

For stompbox designs, you almost always have an input
and an output. Unfortunately, how these inputs and
outputs are represented on schematics is all over the
place. In the most standard form, some of the details
about input and outputs are left off schematics because
these details remain standard across stompboxes.

So when you look at a schematic like this, you are
dealing with a sort of shorthand that the schematic
author used.

Figure 2.1: Shorthand Depiction of Inputs and Outputs

If you look at the input side of the schematic, it is
one wire. But the plug on the end of your guitar cable
has two connectors. WTF? This is an example of
shorthand, and here’s how the schematic maps to the real
world.

Figure 2.2: Mapping Shorthand to the Real World

The tip of the plug always carries the signal, and
the sleeve of the plug is always connected to ground. So
when you see the simplified form, it is assuming you
will connect to tips of your plugs and jacks to input
and output, and both sleeves will be connected to
ground.

There are other ways of representing inputs and
outputs on schematics. For example:

Figure 2.3: Another Way to Show Inputs and Outputs

In this example, a more literal form of schematic
symbol is used for the input and outputs. It shows the
jack part connected to ground. So Figure 2.3 is
electrically identical to Figure 2.1.

Power

Your stompbox circuits will mostly use a very simple
power scheme: a battery or AC/DC adaptor that provides a
positive voltage and a negative voltage. The positive
side of your power supply goes to the part of the
schematic that shows power input, and the negative side
goes to ground. In the case of bi-polar supplies, that
is not the case, but such a supply is not that common so
we cover that separately.

Referring to our simplified schematic form again:

Figure 3.1: Power Representation

You can see that the positive side of the battery is
represented by a symbol denoting + voltage. The negative
side of the battery is ground. There are other forms you
will see in schematics, such as when batteries are
actually shown as a schematic symbol.

Figure 3.2: Battery on the Schematic

So as with other forms of shorthand, Figures 3.1 and
3.2 are electrically identical. One of the drawbacks on
Figure 3.2 is that it is showing a battery, whereas you
may want to connect your circuit to a battery and an
AC/DC adaptor. A small point to be sure, but it
illustrates another example where “schematic shorthand”
can be useful.

To round out this discussion of power and
input/output shorthand, here’s the bo0ster schematic
re-drawn to show grounds in the non-shorthand way:

Figure 3.3: The Revised Booster Schematic

Switching

Another confusing aspect can be the switching
arrangement. For example, when you look at the schematic
in Figure 1.1, there is no on/off switch for the power,
nor is there any switching for bypassing the effects. As
with input and outputs, the design of power switching
and bypass switching is usually assumed. In other words,
we assume that when we build an actual pedal from the
schematic, we will use the standard 9 volt battery clip
wired to the standard 2.1mm DC jack, all in a standard
way.

Because this power scheme hardly ever changes, there
is no real reason to repeat it on each and every
schematic. Similarly with bypass switching: the ubiquity
of 3PDT true-bypass switching is such that it doesn’t
make sense to draw it out in every schematic.

So how do you translate the shorthand of schematics
to the real world of switching and power? We’ll cover
that a little later when we talk about the Stompbox
Harness.

Schematic Symbols

So now that we have the general lay of the land for
schematics, let’s delve into the mysteries of the
symbols themselves. By and large, symbols are fairly
standardized. However there are exceptions that are
introduced to cover the huge array of component types.
In this section, we’ll cover the most commonly used
symbols and point out any variations you might see.

Resistors, Potentiometers, and Trimmers

Resistors are not polarized devices, they work either
way. Resistors are shown as a wavy line, like the R3
value below.

Figure 4.1: Resistor, Potentiometer, and Trimmer
Schematic Symbols

Potentiometers have three connections, so you need to
know how to match up the three connections on a
schematic with the actual pot, like this:

Figure 4.2: Matching Potentiometer Lugs to the Schematic
Symbol

Trimmers, as shown in TR1 above are potentiometers
also, but they are usually small plastic devices
soldered to the board as a “set and forget” type of
affair.

The identification of resistors is simple: The letter
R followed by a sequential number. Potentiometers are
often denoted as VR for “variable resistor” but may also
show up as R. It’s easy to spot the difference just by
looking at the schematic symbol.

Additionally, potentiometer values are shown using
standard code. Potentiometers have very simple codes: a
Letter and a Value. The code is:

A single letter, A for audio/log, B for linear

A Numeric value, i.e. 10K

So a 100kΩ linear taper would be B100K. A 1k audio
taper would be A1K. Finally, potentiometers and
sometimes trimmers) will have an additional label that
denotes their function. So in Figure 4.1 we can see that
the VR1 potentiometer controls the volume.

Capacitors

Capacitors appear on schematics using one of two
basic symbols: parallel lines or a straight line and a
curved line. In the case of parallel lines, the type is
unpolarized, so for our purposes that will mean ceramic
or film capacitor. When the symbol is a straight line
and a curved line, the capacitor is polarized and the
straight line side represents the positive side.
Polarity may also be indicated by a + symbol.

Figure 4.3: Capacitors on Schematics

Diodes

Diodes are polarity sensitive, and the cathode side
is indicated by a colored band.

Figure 4.4: Diodes on Schematics

The following graphics illustrates mapping between
the schematic symbol and the actual device:

Figure 4.5: Diode Polarity Mapping

For stompbox use, you are typically going to use
small signal diodes. These can handle about 100mA of
power. Since a LED is just a special type of diode, it
follows the same convention in terms of having an anode
and a cathode. In terms of packaging, the longer leg is
always the positive side. There is also a flat side,
which denotes the negative side.

Figure 4.6: LED Polarity

Transistors

Transistors almost always have three legs, and the
pin outs (i.e. which leg is the Base, which is the
Collector, and which is the Emitter) can be confusing.
One of the most common reasons a transistor-based
circuit won’t work for you is that you inserted the
transistor wrong. So it is important to look at the
pinout for the specific device.

Figure 4.7: Transistors on Schematics

Integrated Circuits

Integrated Circuits (known as ‘chips’ in the
vernacular) are even more amazing the transistors,
because inside, they contain hundreds or thousands, or
even millions of transistors. ICs are roughly divided
into linear and logic types. Linear types include
operational amplifiers, and logic types include
counters, logic gates, etc.

Because integrated circuits come in some many
configurations, you’ll find there are several
representations for them. The most common IC used in
stompbox circuits is the operational amplifier or opamp.
This has a pretty standard pin out and configuration
across types so it has its own schematic symbol.

Figure 4.8: Opamp Schematic Symbol

We can see that the opamp symbol is a triangle with
two inputs and one output. Opamps have negative and
positive inputs, so those are shown. Also shown are the
pin numbers for the specific opamp.

There are many types of ICs that are specialized
enough that they don’t have their own specific schematic
symbol, so they are drawn as a rectangle or square with
pins shown in whatever order makes sense in the
schematic layout:

Figure 4.9: Generalized IC Schematic Symbol

There are also logic and other types of integrated
circuits that have their own schematic symbols, like
these:

Figure 4.10: Other IC Symbols

Most ICs you will use in stompbox projects are
plastic dual inline package (DIP) devices with a variety
of pin counts and pin outs. Note that the chip
orientation is always denoted by a notch, or printed
dot, on one end.

Figure 4.11: Identifying Pin 1

Schematic Cheat Sheet

The Big Picture: What does Each Part Do?

So now we have a good feeling for how to read
schematics. But what do each of these parts do? Learning
about the function of each component and its complex
interactions both within a circuit, and with the things
that it connects to is the purview of electrical
engineering, and beyond the scope of this article.
However, it is useful to look at a simple example to try
and weave all the things we’ve learned so far back into
a coherent example. So let’s look at the booster schematic
again.

Figure 5.1: A Schematic

We can easily identify the input and output. The
signal you want to modify is presented to the input, the
goo in the middle does the work, and presents is
modified signal to the output. Let’s look at each
component, generally left to right. After the input
jack, there is R1, a large value resistor that connects
to ground. This is something you will see very often in
stompbox schematics—it helps set the input impedance of
the circuit to a level where it doesn’t drag the
guitar’s pickups down to much. C1 is the input capacitor
which filters and DC out of the signal. It also controls
the frequency response of the input signal as it is
presented to the transistor.

R2 and R4 form a voltage divider. This simple snippet
is in charge of providing half of the 9 volt source
voltage as a reference point to the base of the
transistor. This reference point helps tell the
transistor how much to amplify the signal. R3 and R5 set
the gain factor of the transistor, which simply means
that it tells the transistors how many times to amplify
the signal. The signal then goes to C2 which removes the
DC component of the signal.

Finally, we are off to the potentiometer for volume.
The pot is wired as another voltage divider. Depending
on where you turn the knob, you are balancing how much
of the output signal goes tor ground (i.e. thrown away
or attenuated) and how much goes to the output. That’s
it—a single transistor and a handful of components give
you a nice linear boost circuit.

From Abstract to Reality: Let’s Put it on a Board

One of the key reasons to learn how to read
schematics is to be able to speak the language of
electronics, the ability to look at a picture and get a
general idea of what it does and how. But the other more
concrete reason is that you want to actually build
something. Which leads to the central point of this
article: how do you turn a schematic from abstract
symbols to an actual working thing?

The good news is that schematics are not all that
abstract. In fact, in most cases you could lay out your
physical components in an arrangement pretty much the
same as the schematic and then connect wires just like
in the schematic. While that makes sense, it is not
really practical. There are much easier ways to do it.

On the Breadboard

Probably the easiest way to transfer the conceptual
schematic to a physical dimension is to use a
breadboard. Breadboards also have the advantage of
non-permanence—unlike solder you can undo mistakes
easily and experiment with different values. Most
breadboards are conveniently organized in a way very
conducive to stompbox hacking. Take a look at the
following diagram:

Figure 6.1: A Typical Breadboard

You can see that we have positive and negative strips
running down the left and right edges of the board—very
convenient for connecting our various bits to power and
ground. There are also a bunch of “strips of 5”. These
are the places where we can insert components and wires
to form a physical arrangement that maps to the
schematic. (Note that the above breadboard is
representative of one of the most common types, but
others have different arrangements.)

So, to build our LPB-1 Booster on the breadboard, we
simply work through the schematic and arrange components
and wire jumpers. Like this:

Figure 6.2: The LPB-1 Booster on the breadboard

As you trace through the schematic, compare it to the
breadboard. Usually there is an “aha!” moment when you
realize how simple it actually is.

Non-Breadboard Reality

Once you have traced a schematic, tried it out and
want a more permanent solution, there are various
options. This section outlines some of the more common
board techniques.

Perfboard

There are various types of perfboard and the term
itself loosely covers a lot of different designs. The
most common type is pad-per-hole. It looks like this:

Figure 7.1: Pad Per Hole Perfboard

The board itself is made of a rigid insulating
material, and there are rows and columns of holes. On
the pad-per-hole layout, each hole is surrounded by a
copper pad. None of the copper pad/hole combinations are
connected to any others. So you stick your component
through the top side of the board, flip it over, and
solder it to the pad on the other side of the board. You
then solder bare wires to the underside to form the
connections. For example, the following diagram shows
the connection between a resistor and capacitor on a
per-per-hole layout:

Figure 7.2: Pad Per Hole with components

Pad per hole has the advantage that you can layout
your components and wires much like a schematic. The
grid of holes that you work on presents a great way to
match up components on a schematic to an x/y grid on a
board. The disadvantage of pad per hole is that it can
be somewhat tricky to get all the soldering clean and
not have it run and create unwanted solder bridges.
Also, unless carefully planned, pad per hold can lead to
larger board sizes as compared to other mediums. Other
than that, pad per hole is a great way to turn
schematics into reality.

There are other types of boards that fit into the
perfboard category. These usually have bus
connectors—copper traces that connect a group of holes
in interesting ways. For example, Radio Shack sells a
number of perfboards that make it much easier to build
on than pad-per-hole designs. For example, their IC
prototype board makes it easy to supply power (+ and
ground) and use ICs and other devices:

Figure 7.3: Radio Shack Prototyping Board

Prototyping boards like the Radio Shack version shown
above have a big advantage over pad per hole designs:
they have pads pre-connected in ways that make build a
lot easier. For example, look at the middle of the
board. There are two strips of connected pads that run
the length of the board. These are very useful for power
and ground. Similarly, there are groups of 3-connect
pads and groups of 2-connect pads. These make it easy to
connect multiple component terminals which means a lot
less wiring.

Here’s an example of using the Radio Shack board with
an integrated circuit to create a tone generator:

Figure 7.4: Radio Shack Board in Use

Veroboard

Veroboard (also known as stripboard) is a specialized
form of perfboard. It is a name-brand product that
arranges holes along a connected bus. To form circuits,
you make small cuts in the bus trace to match the
schematic you are working on.

Figure 7.5: Veroboard

Veroboard diagrams show where to make trace cuts
(usually with a small Xacto type knife) and where to
place and solder the components. For example, here’s a
layout that shows red dots that signify where to cut the
traces, and a few components shown.

Figure 7.6: Veroboard Explained

Printed Circuit Boards

Printed Circuit Boards (PCBs) are probably the best
way to build things if you are doing more than one, or
want a more professional result. But they require skills
that are sometimes impractical for beginners. In other
words, you can do a lot more learning, testing and
experimenting with the other types of “reality” devices
discussed here. If you want to make your own PCBs, there
are many resources on the interwebz to help you.
Additionally, lots of DIY sites, like General Guitar
Gadgets and TonePad have PCB layout artwork you can
download and use.

Here’s a layout for my Noisy Cricket PCB. Generally,
a layout file will contain both the PCB layout artwork
itself, and a graphic showing the location and
orientation of components for the board.

Figure 7.7: PCB Transfer Artwork

Figure 7.8: Parts Layout Diagram

The Stompbox Harness

Earlier, we talked about all those interesting
shorthand notations found in schematics. Like the fact
that true-bypass switching is usually not shown. Same
for power on/off switching, the battery connector and
the power jack for an AC adaptor.

The following diagram shows a “Stompbox Harness”, a
generalized component and wiring diagram that forms a
generic shell to place your circuit board in. It
features true-bypass switching, and dual power: either a
9 volt battery or an AC/DC adaptor.

Figure 8.1: Stompbox Harness

Note that there are several ways to accomplish true
bypass wiring. Check out the following link from General
Guitar Gadgets for loads of information on true-bypass
wiring options.

http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=33&Itemid=27

DIY Layout Creator

No discussion of creating circuit boards would be
complete would be complete with a nod to a fine fellow
named Bancika. He created a free piece of software
called DIY Layout Creator that is a work of genius. DIY
Layout Creator allows you to graphically draw layouts
for projects, using pad per hole, veroboard, or printed
circuit boards as your medium.

Figure 9.1: The Incredibly Cool DIY Layout Creator
Software

As you can see from the above screenshot, you have a
list of drag-and-drop components on the left, a design
area in the middle, and an explorer on the right. DIY
Layout Creator would be cool if it was the product of a
team of software engineers from a big company. But from
a single guy toiling away to develop a free program, it
is simply incredible.

If you are going to be doing anything of consequence
in stompboxes, I highly recommend you download this
program, give it a try, and then send a quick donation
to Bancika—he’s a cool guy.

http://www.storm-software.co.yu/diy/index.php?project=software

Finally, there is also a huge library of layouts for
you to freely download, including pad per hole,
veroboard and PCB layouts at the same site.

http://www.storm-software.co.yu/diy/index.php?project=layouts

Resources

Thanks to google, the world really is at your
doorstep. Here are some useful places to go as you work
with schematics, layouts, and boards.

What

Where

Great gallery of
layouts including pad per hole, veroboard, and
PCB designs

www.aronnelson.com/gallery/main.php

Bancika’s DIY Layout Creator
Software

www.storm-software.co.yu/diy/index.php?project=software

Layout Library for DIY Layout
Creator

www.storm-software.co.yu/diy/index.php?project=layouts

General Guitar Gadgets: Lots of
projects and layouts

www.generalguitargadgets.com

Runoffgroove: Lots of projects
and layouts

www.runoffgroove.com

Tonepad: Lots of projects and
layouts

www.tonepad.com

DIY Stompboxes: THE forum for
diy stompbox stuff

www.diystompboxes.com/smfforum

PCB Layout for Musical Effects:
R.G. Keen's comprehensive book on doing layouts
right.

www.smallbearelec.com/Detail.bok?no=679

Conclusion

I hope that this short article has cleared up some of
the mysteries of schematics for you. Of course there are
a thousand more details, variations and confusions as
you start learning to read schematics and transfer them
to the real world. But hopefully you have a basic
understanding of how they work, and how they map to the
real world.

As always, I love to hear feedback, corrections, and
even the occasional flame. Pop me an email at dano/ at /
beavisaudio.com

(c) 2005-2012. Some Rights Reserved - This work is licensed under a
Creative Commons License