by Bryan Bergeron, Editor by Bryan Bergeron, Editor
How Do They Do That?
Reverse engineering is one of the most challenging and rewarding endeavors in electronics. I’m talking about
replicating the functionality of a device that you’ve seen
or read about but that’s too expensive or otherwise
unavailable. There are numerous issues involved in reverse
engineering — from creating a schematic to locating parts.
Moreover, you have to understand what’s going on, both
mechanically and electronically. In my experience,
seemingly simple devices are often the most challenging.
However, there are methods you can use to glean an
understanding of just about any device on the market.
Case in point: I’d been lusting over a guitar
synthesizer since it was introduced a couple years ago.
According to the marketing literature, it was based in part
on filter technology used in relatively inexpensive effects
boxes. I managed to snare one of these effects boxes on
eBay and — within hours of arriving — I had it
disassembled on my workbench. Teardowns are one of
the best ways of figuring out not only how a circuit works,
but how to best assemble it.
Next, I searched for technical reviews that described
how the synthesizer worked. As is typical, I had to piece
together information from several reviews to get an
understanding of the circuit and operating conditions.
One article mentioned an external power supply, another
special pickup designs, and so on. It seems that the
marketing people for many companies won’t divulge
everything to one reviewer, but are fine with disclosing
different aspects of their technology to different reviewers.
Armed with the information from the teardown and
reviews, I started drawing up plans for a circuit board that
I’d embed in one of my guitars. It wasn’t much – a
microcontroller, a few op-amps, a couple transistors, a 9V
battery, and a handful of capacitors and resistors. Three
weekends later, I had a circuit that checked out on my
workbench. The next step was to test it with the guitar.
Inexplicably, it didn’t work. Electrically it checked out, and
in side-by-side comparisons with the teardown, everything
seemed in order. But there was something missing.
Perplexed and frustrated, I turned to my favorite
source of technical information: the US Patent and
Trademark Office ( www.uspto.gov). If you’ve used
Google, you know how to search the USPTO database. In
fact, you can use Google’s patent search engine
( www.google.com/patents) instead of the USPTO site.
Unless you need to run a complicated, multiple-keyword
search, the Google site is a good first stop.
In the patent files, I located several patents that
explained exactly how to integrate a synthesizer into the
body of a guitar. It turns out that I got the electronics
correct but I hadn’t considered the
magnetics. Specifically, the angles
of the magnetic pickups used to
capture the vibrations of the steel
strings relative to each other are
critical. In a typical guitar, the
magnetic pickups are mounted
parallel to each other and
perpendicular to the strings.
However, in this particular form of
guitar synthesizer, the magnetic
pickups operate best when the axes
are about 30 degrees apart.
I hadn’t thought of the
magnetic properties of the circuit.
However, thanks to information
from the USPTO, I was able to align
the pickups and test the circuit.
Admittedly, my guitar synthesizer
falls short of the real thing. That’s
something I’m willing to put up
with, given my DIY guitar
synthesizer cost less than one