Issue 632 • 25 May – 7 June 2022 37We were even able to power a BBC micro:bit
wirelessly using our microUSB Qi receiverAdd wireless charging to your phone
Next issue: Convert your handwriting to digital text
The Qi standard was established in 2008,
and has been revised several times
since, most recently in January 2021.
However, the underlying technology –
electromagnetic induction – is older than
you might imagine. Indeed, the principles
were first described by Michael Faraday
(pictured) in 1831.
Faraday created two metal coils, one of
which he connected to a meter that would
show the level of energy passing through
it. He then connected the second coil to a
battery. Even though there was no direct
connection between the two coils, the
meter plugged into the first coil twitched
at the moment the battery was connected
to its neighbour, and did it again when the
battery was disconnected. Clearly, the
energy flowing through the second coil
was interacting with the first, which was,in effect, generating its own
power.
Faraday’s discovery
has many applications
around the home. It’s most
commonly found in electric
toothbrushes that charge on
a stand rather than needing
to be directly plugged in –
and, of course, in wireless
phone chargers.
A Qi charger base station
contains a large copper coil
that remains on standby
most of the time. Inside your phone, or a Qi
charging receiver like the ones we’re testing
here, you’ll find a similar though usually
smaller coil. There’s no technical reason for
the different sizes. Rather, the coil in your
phone is small because there’s no room forHOW QI CHARGING WORKS
full charge in one hour, seven minutes
(see screenshot below left). The Motorola
Moto G7’s larger 3000 mAh battery was
fully charged in four hours, 52 minutes.
In each test, we charged without a case
on the phone for optimum results. The
product listings are slightly contradictory
on this point, both warning against
using a case at all and, elsewhere,
recommending “if you use this item with
a phone case, please confirm your case is
charge. Apple itself has yet to produce an
iPad with wireless charging.
On a geekier level, we plugged the Qi
receiver with microUSB connection into
a BBC micro:bit (www.microbit.org) and
repeated the experiment (as pictured
above). In this case, the micro:bit, which
has no internal battery, booted up, and
was ready to use within a couple of
seconds.ultra thin, and please don’t use a metal
case, cards and other objects that may
block the signal”. This advice is sound,
with any case having the potential to
reduce the effectiveness of any wireless
charging connection – even if using a
phone’s built-in receiver.
In practice, however, the Qi standard
allows for distances of up to 4cm (1.6in)
between the charging pad and receiver
although, at those distances, we would
expect performance to be less than
optimal. In our house with four Qi
charging pads and stands of different
brands, we’ve yet to encounter one
that works over such distances. We do,
however, routinely charge our phone
wirelessly without first removing its
rugged case.3
Charge iPads and
other devices
Adding wireless charging using
a Qi receiver is a quick and easy upgrade,
largely because the receiver itself works
much like a regular cable. In theory, you
could attach it to any device that draws
less power than its rated output, and
use it to charge it – or even power it –
wirelessly.
To test this theory, we connected a Qi
receiver with Lightning connector to a
10.5in iPad Pro and placed it on a Yootech
Wireless Charger (£17 from http://www.snipca.
com/41799, pictured left). It recognised
the connection, and the iPad started toa large one, and the coil
in the charger is larger
because it gives you an
easier target to hit when
lining them up. If both coils
were as small as the one
in your phone, you’d need
to be quite precise when
dropping your phone on to
the charger.
When you place your
phone on a Qi charger, the
two coils register each
other, and a current, drawn
from the connected lead and adapter
plugged into the base station, is applied
to the base station’s coil. This is registered
by the coil in the receiver, and used to
generate electricity, which is fed as a direct
current (DC) to the internal battery.We managed to charge an iPad Pro using the
Yootech Wireless charger