switch for power brick: Nothing is simpler than an on-off
switch, yet most power bricks, chargers, and the like do not have a
switch. This is of no consequence if you are charging your phone, but
what if you are powering a Raspberry Pi—or
a project breadboard. It
would be nice, not to
have to pull the plug when cycling power. Of course there are
countless ways to add a switch. I prefer a latching pushbutton on the
enclosure top for two reasons: First, I have a bunch of them, and
second, switching by pushing down from on-top does not cause the nearly
enclosure to tip over. The
switch’s input and output connections can be as
as cutting and splicing the power supply’s DC wire. If the parts
bin includes DC power plugs and jacks, consider making the switch box
pluggable. Similarly, an LED
indicator (lower-right in photo) enhances the setup.
On the subject of tipping things over, stick-on
tire weights can be used for adding weight to a tippy enclosure. This
would not be necessary for the illustrated enclosure, but many amateur
electronics projects are not much heftier than an empty box. In
such cases adding sufficient weight improves their stability and
Indicator LEDs: I use Anderson Power Poles for
everything 12 volt. These genderless connectors are ideally
suited for connecting different rigs or
devices to different power supplies, or for running the same rig in the
house and car, etc. Sometimes you want to know if a voltage is present
at one of these connectors. For example, you may not remember whether
or not the cable was left connected to the car or boat battery, or was
unplugged. A portable voltmeter works, but this pocket tester is
handy, and may be conveniently stored with a supply of connector parts:
a similar vein, if you use breadboards for prototyping circuits, it can
be helpful to have one or two or a few pluggable LED’s for
quick-testing key circuit points. A variety of pin-header spacings
could be used. Be sure to mark polarity. I use the stripped ends from
plastic-insulated hookup wire to mark the plus side (heat shrink is no
good on bare wire).
Different color LED’s
vary in brightness, blue being the brightest. I generally use
1000 ohms or more in series with blue LED’s, and 330 or 470
ohms (for current limiting) with dimmer colors.
Brackets: PCB’s and generic prototyping boards often have
very tiny corner mounting
holes—or if you cut the PCB’s as I do, no holes at all in some cut off
parts. An alternative
way to mount PCB’s in an enclosure or other framework is to use slotted
brackets, where the slot width matches the PCB thickness. This simple
application is one
of many good uses for a 3D printer. See also item 5 below.
I use FreeCAD for custom designs. FreeCAD has a built-in
spreadsheet option that can be used to specify the variable
dimensions of a design, including computed dimensions. The latter could
the location of mounting holes as a function of the
slot bracket’s lip length and width. Thus a single FreeCAD design can
accommodate multiple PCB sizes and
shapes. To print brackets for a different PCB simply change relevant
dimensions in spreadsheet cells. It is not necessary to edit part
properties directly as these just name the spreadsheet cells (or
4. Polarity-safe PCB:
A few of the low power kits I have assembled include a diode in series
with the power connector. If you accidentally connect the 5 or 9 or 12
volt power supply backwards, nothing happens. The circuit doesn’t work
but neither does it transmit a smoke signal in place of the audio or RF
that was expected. I have wondered if substituting a full-wave
rectifier for the diode would not only prevent damage but also permit
the circuit to work, regardless of which way DC power input was
connected. I have not tried this, however I have used a different
scheme for powering circuit boards that ensures that power can only be
applied with the correct polarity.
projects power typically connects to pin headers on the circuit board.
Two pins are needed for + and – but if only two pins are used, it is
possible to accidently connect them backwards. This assumes ordinary
pin headers, not a socket that only accepts one-way connections. The
simple trick is to use three pins, making the middle one + and the two
outer ones – (see photo). It is still possible to go wrong if the
supply end does not also use a 3-pin (usually female) header.
Obviously if only two pins are used on the supply side, it would
still be possible to generate smoke signals.
While on the subject of headers, I have a suggestion for soldering them
to PCBs. Male pins transfer heat effectively from the underside of the
PCB to the top where your finger might be if you haven’t previously
experienced the consequences of using a finger to hold the header.
Actually I have two suggestions for this. First, temporarily
insert the male pin header into a female header. A lot less heat will
reach the finger if holding the assembly by the edges of a female
header. Suggestion #2, use cellophane tape in place of a finger to
steady the assembly in approximately the desired orientation. When one
pin has been soldered, remove the tape and reheat the joint while
jiggling the assembly until it is solidly against the PCB with pins
Cellophane tape is better
than a jig for many purposes. For example, suppose you want to
solder a bare wire to use as a ground bus on the bottom of the board.
One trick is to bend the wire ends up through holes temporarily, but
that may not be feasible in every case. Equally effective is to tape
the wire to the board until one part has been soldered, and the wire no
longer wants to move about. I have also used cello tape to hold a DIP
socket in place, or a crystal, or really anything that tends to move
while in the process of being attached.
Beautify: Bezels are generally thin and flat and
make another ‘easy’ 3D-printer project. The
reward to investment ratio is good, although there comes a
point where beauty can morph into clutter.
As I think about it, there are many ‘easy’ things to do with a
3D-printer. The small spacers (left) are perfect for mounting a
16x2 LCD in a panel cutout. It takes only about 10 minutes to
print a set of 4. As with the PCB mounting brackets, different
diameters and lengths can be printed from a single graphical design, by
editing one or two spreadsheet cells.
course 3D printers are not as common or
inexpensive as soldering irons. Perhaps the hard part is to acquire a
3D printer and learn to make it work and, after that, to keep it working!
Repurposed Tablet: What to do with an old tablet? The
battery is dead and cannot be replaced for less than the cost of a new
tablet. One admittedly niche use is as
a hotspot activity monitor. A browser (Chrome, in the
illustration) connects to the MMDVM hotspot wirelessly. In my
setup the Google Nexus
tablet sits on the desk
next to the radio. Of course, since its battery is dead the tablet has
plugged in all the time. The screen is set
to the dimmest level that is bright enough for daytime viewing. The
timeout (sleep). In this configuration the tablet acts as a dedicated
While it does not lose its connection to the
hotspot, and the screen remains illuminated 24-7, I have not figured
out how to keep the DMR gateway connection alive for more than
without transmitting briefly. (Problem solved—See footnote1) Nor have I thought how to
the Internet an
interesting exercise! (Problem not solved) Seriously, though, the
dedicated monitor concept can be applied
in multiple ways, for example, to show APRS activity, or amateur radio
satellites status, or high frequency propagation, or any sort
of actively updated information.
1. The disconnect
out to be specific to
Talkgroup 310. Upon switching to TG 3100 (as in the illustration) the
Gateway Activity monitor no longer lost its connection in the wee
hours. As of this writing it has remained connected for several
weeks without having to reload the page or goose the connection via RF.
Project descriptions on this page are intended for entertainment only.
The author makes no claim as to the accuracy or completeness of the
information presented. In no event will the author be liable for any
damages, lost effort, inability to carry out a similar project, or to
reproduce a claimed result, or anything else relating to a decision to
use the information on this page.