Electronic Building Blocks
By Julian Edgar
Great results on a low budget
Quick and easy construction
Wireless phone charging pad
S
omething a little different this month – I recently
bought a handy item that was so cheap it didn’t matter if
I broke it, which I ‘did’ – more on that below! I wanted to
experiment with it and I suspect many of you would enjoy it too.
If you have an up-to-date mobile/cellular phone, you’ll be
aware that it probably has a wireless charging function. You
simply lay the phone on the flat pad and, as if by magic, it
charges. (Of course, not much magic is involved – it’s being
charged inductively.)
Commercial inductive chargers are available, but if you want
to have a play with the technology, this little module lets you
explore to your heart’s content – and at a cost of under £4,
delivered. To find it, do an eBay search under ‘PCB Circuit
Board Wireless Charging DIY Transmitter Module Micro USB
Port Stable’. (For example, at the time of writing, eBay item
254688491954 costs £3.68 including delivery.)
The assembly is 83 × 71mm and about 2.5mm thick. While
some of these modules use separate inductive coils, this one
places the coil in an opening in the centre of the PCB. The
module is powered via a micro-USB port – cable not supplied.
(You probably have one in your spares box – lots of equipment comes with them.) Surface-mount LEDs are positioned
around the outside of the PCB. These glow green when power
is first turned on and then blue when charging. The board has
over-temperature protection (60°C) and is said to have intelligent over-voltage and over-current protection.
Input current is specified as 2A and maximum charging current is 1A. However, transfer efficiency is rated as 75% – so
make of those numbers what you will! In use, I measured a
maximum current draw of 0.8A.
The module uses the QI wireless charging standard. Manufacturers using the standard include Apple, Asus, Google, HTC,
Huawei, LG Electronics, Motorola Mobility, Nokia, Samsung,
BlackBerry, Xiaomi, and Sony. However, that said, this module didn’t work with my first-generation Apple watch, but did
work with a current iPhone.
So – and here’s the big question – at what distance will the
module charge the phone? The specifications state that the best
distance is 2-5mm, but that charging can occur at up to 8mm.
Of course, place anything between the coil and the phone and
that distance decreases.
Mounting
Fig.1. The inductive charging module comprises the charging coil and
a surrounding PCB. LEDs around the outside of the PCB make the
charger quite colourful in action. Cost is under £4, delivered.
64
I must admit that mounting the device initially had me a bit flummoxed. For an electronics workbench or similar, I’d be tempted
to just glue it to a baseboard made from a piece of wood. However, that risks scratching the back of the phone each time it is
placed on the charger, so I took a different approach.
Using 3mm screws, nuts and nylon washes I attached the
module to the underside of a plastic lid taken from a cheap
kitchen storage box. The plastic lid is semi-translucent, so the
operational-status indicator LEDs can be easily seen. However, mounted in this way, the coil sags away from the lid – not
wanted. I drilled another hole so that the coil (which has a
central hole) could be spaced a short distance away from the
lid with the same screws/nuts/washers approach as was done
for the PCB. However, I found that using a steel screw stopped
the inductive coil from working. I then replaced it with a nylon screw, and then finally, removed the spacers on this screw
and drew the coil up flush against the underside of the lid.
Practical Electronics | February | 2021
Fig.4. The charger in action. My phone
rests on the raised lip around the edge
of the lid, so the back of the phone
doesn’t touch the screw heads.
Fig.2. The charging module mounted to the
underside of a lid taken from a translucent
kitchen storage container.
Fig.3. The magnetic induction disc is held
in place with a single nylon screw and nut.
Be very careful when tightening the nut as
the disc can easily crack – as shown here.
(The device still worked OK, even with the
cracked disc.)
Then I made a mistake – and tightened
this screw. The magnetic disc cracked
in multiple places – so be careful not to
tighten this screw too much! (The module still worked fine though.)
Four more holes were drilled to allow
for standoffs to be screwed into place,
one each corner of the plastic lid and so
providing four feet on which the charging
pad stands.
Note that the plastic lid has a raised
ridge around its periphery, and the phone
rests on this lip. That is, the phone’s back
never touches the heads of the screws.
This mounting approach gives a distance
between the charging coil and the phone
of about 4mm, including the thickness of
the plastic lid. Mounted in this way, the
module charged an iPhone without issues.
Summary
This module is cheap enough to experiment with. But be aware that if you, say,
have the cute idea of sticking the module to the bottom of your desk and then
just laying your phone in the right place
to charge, it won’t work – not unless the
top of your desk is very thin indeed!
Note also that this charger will be
slower to charge a phone than a wired
connection, and also a little more wasteful of power. That said, it’s also very
convenient to just lay your phone on the
pad and watch it charge!
Teach-In 8 CD-ROM
Exploring the Arduino
This CD-ROM version of the exciting and popular Teach-In 8 series
has been designed for electronics enthusiasts who want to get to
grips with the inexpensive, immensely popular Arduino microcontroller,
as well as coding enthusiasts who want to explore hardware and
interfacing. Teach-In 8 provides a one-stop source of ideas and
practical information.
The Arduino offers a remarkably effective platform for developing a
huge variety of projects; from operating a set of Christmas tree lights
to remotely controlling a robotic vehicle wirelessly or via the Internet.
Teach-In 8 is based around a series of practical projects with plenty of
information for customisation. The projects can be combined together
in many different ways in order to build more complex systems that can
be used to solve a wide variety of home automation and environmental
monitoring problems. The series includes topics such as RF technology,
wireless networking and remote web access.
PLUS: PICs and the PICkit 3 – A beginners guide
The CD-ROM also includes a bonus – an extra 12-part series based around the popular
PIC microcontroller, explaining how to build PIC-based systems.
EE
FR -ROM
CD
ELECTRONICS
TEACH-IN 8
£8.99
FREE
CD-ROM
SOFTWARE
FOR
THE TEACH-IN
8
SERIES
FROM THE PUBLISHERS OF
INTRODUCING THE ARDUINO
• Hardware – learn about components and circuits
• Programming – powerful integrated development system
• Microcontrollers – understand control operations
• Communications – connect to PCs and other Arduinos
PLUS...
PIC n’MIX
PICs and the PICkit 3 - A beginners
guide. The why and how to build
PIC-based projects
Teach In 8 Cover.indd 1
04/04/2017 12:24
PRICE
£8.99
Includes P&P to UK if
ordered direct from us
SOFTWARE
The CD-ROM contains the software for both the Teach-In 8 and PICkit 3 series.
ORDER YOUR COPY TODAY!
JUST CALL 01202 880299 OR VISIT www.epemag.com
Practical Electronics | February | 2021
65
