W
hat is a ruler? A piece of plastic, wood
or metal you can use to measure
lengths and draw straight lines. PCB
rulers, though, are different – and not just
because they’re almost completely inflexible,
being made out of rigid fibreglass and copper.
Sure, you can use them to measure lengths
or draw straight lines, but they’re designed to
act as desk-based reference guides too.
Bolt Industries’ Ian Dunn is no stranger to
PCB rulers. Now on his third generation of
crowdfunded PCB ruler designs, he’s been
refining his art – and the latest design packs
a wealth of information into a surprisingly
small space. The front of Dunn’s latest ruler
design carries, as you might expect, length
markings in inches and millimetres. These start,
pleasingly, right at the edge, so you can push the
smaller edge up against the object you want
to measure.
The bulk of the front, though, is taken up
by pin-out references for a range of popular
microcontrollers: The Arduino Nano, Arduino
Micro, Teensy 4.0 and Raspberry Pi Pico (see
Issue 212), which replaces the Adafruit Metro
Mini reference from earlier designs. There’s
also a reference for the 40-pin general-purpose
input/output (GPIO) header on Raspberry Pi
single-board computers.
Each microcontroller is represented as a full
footprint, making it easy to figure out which pin
is where on the physical device. The references
continue on the back, where you’ll find guides
for common through-hole components,
and mils, plus the
maximum current they can
carry. Next to these are a number of holes
through which you can push wires in order
to get their measurements in American Wire
Gauge (AWG). There’s even a reference guide
for font height.
Compared with earlier designs, Dunn’s
latest ruler focuses a little less on component
footprints and more on references. The seven
switch footprints of the 2nd-generation rulers
have been dropped to just two, making room
for a new reference guide to logic gates
Meanwhile, the USB pin-outs have been
dropped altogether, and the footprints for
capacitors have been replaced with a guide
to reading the numerical codes printed on the
front of ceramic disc capacitors. While the new
design makes it harder to pull a component
out of your bits box and quickly figure out its
footprint, it’s definitely more useful as a general
guide to electronics.
Following a successful crowdfunding
campaign on Kickstarter, Dunn is taking pre-
orders for the rulers on indiegogo.com at $14
US (around £10 ex VAT). Alternatively, the PCB
production files are available to download from
custompc.co.uk/PCBRuler under an open-
source licence.CUSTOMISATION / HOBBY TECH
REVIEW
Bolt Industries PCB rulers
including various switches and
LEDs, resistors, capacitors, transistors,
voltage regulators and diodes.
It’s not just symbols and pin-outs either – the
resistor section includes a guide to decoding
the colour bands, and the LED section has a
reminder of which leg is the anode and which is
the cathode. Likewise, the capacitor section has
a three-way conversion table between micro-,
nano- and pico-farads, and the transistor
sections looks at the inner workings of PNP,
NPN, NMOS and PMOS transistors. There’s
even a copy of Ohm’s law, plus a table of
common diode types and their ratings.
Dunn isn’t done there though. For those
looking to design their own PCBs, or reverse-
engineer someone else’s PCB, there are
copper traces to the left of the ruler, which
include their measurements in millimetresGareth Halfacree is a keen computer hobbyist, journalist, and author. His work can be found at freelance.halfacree.co.uk @ghalfacree
Ian Dunn is back with another reference ruler design, a
follow-up to the pictured 2nd-generation variant
The latest variant adds a pin-out for the Raspberry Pi
Pico, and revises the references on the rear
The rulers provide quick reference for common
device pin-outs, as well as resistor colour codes
and Ohm’s law