In this schematic showing the circuit that
you just built, the double-throw switch has
completed a circuit with the battery, so that the
battery charges the capacitor.
In this schematic, the double-throw switch is
in its other position, completing a circuit from
one plate of the capacitor, through the resistor
and the LED, back to the other plate.
Capacitor
charging
Capacitor
discharging
SCHEMATICS
There are two symbols for capacitors.
A polarized capacitor, such as an electrolytic,
is on the left.
A nonpolarized capacitor, such as a ceramic,
is on the right.
Some people use the symbol on the right
everywhere in a schematic, and let you decide if
you want to use an electrolytic capacitor, and if
so, which way around it should be.
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This article is adapted from the book Make:
Easy Electronics, available at makershed.com/
platt and other booksellers. A complete kit of
all components used in the book is available at
protechtrader.com/easyelectronics.
YOU MIGHT THINK:
A capacitor may seem similar to
a battery. After all, they both store
electricity.
A battery, however, uses chemical
reactions, and even a rechargeable
battery wears out after a limited
number of charging and discharging
cycles.
A capacitor does not use chemical
reactions, and can still work as well
after several years.
Here are three fun projects I’ve built
with my salvaged computer parts
PROJECTS:
Salvaging PC Parts
Pick and Pull
PC Projects
Written by Samer Najia
104 make.co
When I first started my IT consultancy years
ago, I set up a series of computers to function as
servers, and a variety of dedicated workstations
to test software. For the most part, each of these
machines was hand built and configured to suit.
Then one day I moved them all to a server facility
and virtualized them, and suddenly I had a whole
bunch of high-power computers eating up a
ton of room in my garage! It was time to either
tear them apart or sell them — or better yet,
repurpose the best of them.
I’M BURIED IN COMPUTERS
I knew well enough how to take computers apart,
but multiple trips to Take-Apart events had also
taught me the innards of laptops and printers and
peripherals, and I was harvesting LCD panels,
drives, and power supplies. It wasn’t long before
my friends were handing me their old equipment
to harvest parts from. I had bins full of all sorts
of goodies for building network storage devices,
media servers, Linux boxes, and so on. And I
wanted to do something interesting with it all.
I started working on a couple of projects that
were near and dear to my heart, and both were
going to need computers. Powerful computers.
Of course, computers don’t need to live in a PC
case to be useful, so I’ve let myself be creative
with their integrations. Here then, are a few of my
really cool uses for old computers.
PROJECT #1: 3D Printer with
Embedded Computer
I always hated the idea of tying up my laptops to
run my 3D printers. There are printers that are
effectively standalone machines that can do their
own slicing and processing and then of course
controlling. And sure, a single-board computer
like a Raspberry Pi can do some of that, but I
wanted my project to really be standalone and do
everything. I decided I needed to embed a full-
blown computer into my printer — and why not?
I had more than enough parts. To me, the whole
idea was all pros and no cons:
»
The 3D printer no longer needs a separate
computer and can do its own slicing using any
software that runs on Windows (this is not
really as easy to do with Macs)
MATERIALS
Scavenged computers and peripherals
These yield lots of useful parts:
» Motherboards
» Memory on the motherboard
» Hard drives
» Power supplies
» Fans
» Power and reset switches You can buy
standalone switches that plug right in to the
motherboard from various vendors on Amazon
and eBay if you can’t remove them from the
computer case
» LCD displays
» Screws and brass standoffs
» Keyboard and mouse
» Assorted OEM driver boards, USB dongles,
and peripherals depending on your project
» Aluminum extrusion and brackets, 3D printed
parts, plywood, acrylic sheet, veneers, etc. for
making custom enclosures
TOOLS
» Jigsaw
» Screwdrivers
» 3D printer (optional)
» Allen key sets
» Wrenches, socket and standard
» Ruler and measuring tape
SAMER NAJIA holds
a degree in mechanical
engineering from Duke
University but making
things is his true
passion. He spends
countless hours building progressively
larger and more complex projects. He’s
co-author of the new book Mechanical
Engineering for Makers: A Hands-on Guide
to Designing and Making Physical Things,
available at makershed.com/books.
105
makeprojects.com
Adobe STock - damrong, Samer Najia
»
Remote control of the printer is simply a
Remote Desktop connection
»
It can act as a server and be accessed remotely
using a web browser (with some configuration)
»
I can run just about any file or software I want
and worry less about processing power
»
I can upgrade software and hardware anytime,
add peripherals and capability, even replace
the motherboard and reconfigure the operating
system with little to no loss of the installed on-
board software.
The printer I chose for this project is an FLSun
Cube — an H-bot style printer with a larger print
bed. It’s fabricated from 80/20 type extrusions
and, like most PCs, is essentially a box. With a few
modifications to extend the chassis, it can host
a motherboard, ATX power supply, hard drive,
fans, and wiring. Here were some criteria for the
computer parts I chose:
»
The motherboard had to have an onboard video
display card and preferably HDMI, because I
didn’t want to consume space with a vertically
standing video board in a PCI slot.
»
The computer had to have at least 5 onboard
USB ports: for the 3D printer itself, a Wi-Fi
dongle, a wireless keyboard dongle (if your
board already has Wi-Fi and Bluetooth radios
on board, even better), an external storage
device (just in case), and a combination wired
keyboard and mouse. I had several laptops that
fit the bill, but preferred to empty my parts bin.
»
I wanted to use a smaller harvested LCD with
a commercial OEM controller board (which
means eBay or Amazon it seems these days). I
used an 11" LCD pulled out of an old notebook
computer. I could just as easily have purchased
a standalone HDMI-based LCD (even a
touchscreen), but again, parts bin...
»
The hard drive needed enough storage to
install all sorts of software and of course to
store any printer-specific G-code or 3D models.
I used one from my old servers.
The outcome: a completely standalone computer/
printer hybrid (Figure
A
). Notice the white 3D
printed parts that raise the printer up enough to
build a box underneath; these are from various
designs I found on Thingiverse and modified
PROJECTS: Salvaging PC Parts
106 make.co
A
B
Samer Najia
slightly to suit my purposes.
Figure
B
shows the printer’s interior with side
panels and fans installed. The floor of the box
is plywood, cut to suit and covered with a piece
of lamination meant to look like carbon fiber.
You can see the motherboard standoffs being
installed. Notice the rear panel containing the
power socket.
In Figure
C
, the motherboard is installed,
oriented correctly and ready for the rest of the
components. It was important to test-fit first and
consider how the cables lay out and how easy it is
to install wiring and plug or unplug things.
And here’s everything installed in the printer
base (Figure
D
). Notice the two power supplies
(for computer and printer) and the hard drive
in the back, as well as how the SATA and USB
cabling are routed. There are also two power
plugs in the back of the printer.
PROJECT #2: Custom Flight Simulator
I wanted to upgrade my home-built flight
simulator to have more power and feel more
like a real airplane. That meant building an
panel, seat, and controls that are close enough
to the real thing to feel like it. I had a bunch of
instruments from the previous iteration, a few old
LCDs, and a bunch of 80/20 extrusions. And of
course, I had some of those computers.
I wanted my simulator to be able to do most of
what the expensive desktop simulators do, and to
be upgraded at will. The computer had to support
additional instruments and aircraft models, which
might mean more monitors and more USB ports.
I also had plans to add more computers to the
system to run more instruments and controls.
Finally, the simulator had to be mobile enough to
roll around and fit through a standard doorway.
Once a frame was assembled, the next step
was to come up with a panel layout. I arranged
the purpose-built instruments in a logical
sequence (radios and GPS to the right, main flight
instruments to the left) with a harvested LCD as
the main instrument display so that I can show
analog gauges or a moving map. Controls were
arranged for the pilot of a fixed-wing aircraft (left
seat in the cockpit, with throttle controls on the
right). I used a boat seat I found on Amazon, and
because I wanted it to be adjustable I made a rail
system for it using V-slot wheels and parts from
an old CNC machine.
One critical decision: where to park the
computer and its parts? I found myself constantly
opening and closing the case as I changed
video boards, added USB capabilities, changed
the power supply, fried the hard drive and
had to replace it. I finally chose to integrate
the computer into the simulator itself so that
when I upgrade it, I won’t have to revisit all the
wiring and space allocations. I mounted the
motherboard, hard drive, and power supply
directly under the seat so I can change out parts
anytime, while still encasing them. The box under
the seat can be covered by a sheet of acrylic while
leaving the bottom open to allow airflow.
Here’s the simulator at its home at my flight
school (Figure
E
, next page
). You can just about
make out the motherboard toward the bottom of
the image, and the power supply is to the right.
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makeprojects.com
C
D
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