This is only a preview of the February 2020 issue of Practical Electronics. You can view 0 of the 80 pages in the full issue. Articles in this series:
|
Practically Speaking
Hands-on techniques for turning ideas into projects – by Mike Hibbett
PCB digital microscope
C
omponents are getting
smaller and none of us are getting
younger, which means diminishing eyesight makes assembling electronic
circuits increasingly difficult. In fact, even
if you have youthful 20-20 vision, some
SMD (surface-mount device) assembly has
become almost impossible without aids.
In the 1980s, a typical surface-mount
device measured 2.0 × 1.25 mm. As a
young engineer, these components were
no problem to solder before the first cup
of coffee, but 30 years later and after a lifetime of caffeine and day-long sessions in
front of a computer screen, reading glasses
are not enough. Glasses are great for reading books and restaurant menus, but the
fine motor control and clarity of vision
required to place solder and position an
iron tip precisely on these tiny components becomes increasingly challenging.
The solution is the inclusion of some
form of desktop visual magnification.
All professional PCB assembly houses
use visual magnification tools in manual
re-work and repair stations (mainly we
suspect because the people employed
in this work are more experienced, and
therefore a little older!)
We were lucky to obtain an old Nikon
Stereo PCB inspection microscope many
years ago, and it probably cost over a thousand pounds when new in the 1970s. Its
construction quality is fabulous and will
probably continue to serve the next generation. It’s a joy to work with and we
have spent days at a time soldering boards
while peering through it. These vintage
microscopes are, however, very expensive
when bought new, and good ones are hard
to come by second hand. The author’s microscope (shown in Fig.1) is over 40-years
old and ones of a similar age still sell for
over £200. So what are the options for
people keen to obtain some assistance?
What to use?
There is a wide range of options available
on the market within a reasonable price
bracket and, depending on your needs, a
perfectly adequate solution can be found
for home use. Generally performance is
linked to cost, and performance in this
case means:
n Comfort in use
n Optical quality
n Magnification range
n Image capture to PC
n Physical build quality
First, let’s talk about options to avoid. Lowcost ‘watchmaker’ glasses found on eBay
are useless. They have a fixed magnification, and you have to have your face very
close to the work surface, and hold your
head still. Expect to burn your nose while
soldering. Handheld lenses, popular and
effective for reading books are cheap but
require you to hold them – ‘losing’ one
hand, and making soldering impossible.
Budget optics
A 10cm magnifying lens attached to a
‘helping hands’ stand like that in Fig.2
is a fair solution and prices start around
£10, but of course they only give a single
level of magnification. These are a reasonable starting point and we have one
in our lab, mainly for soldering wires to
connectors. They are of limited value for
working with small surface-mount components, but at such a low cost are well
worth adding to your collection of tools.
At this price point it’s also worth adding
a ×3 magnification ‘eye loupe’, as seen in
Fig.2 next to the helping hands.
Basic digital microscopes
Cheap digital PCB microscopes – essentially a webcam on a stand – have become
the modern solution to the problem. The
image is displayed on a computer screen
that you place in front of your work area,
or on a small LCD display mounted on the
stand itself. Avoid the latter – these small
LCD displays cannot provide the clarity
required. Again, performance is linked
(Left) Fig.1. The author’s high-quality Nikon PCB microscope; and (right) Fig.2. Helping hands magnifier and loupe – useful but basic.
52
Practical Electronics | February | 2020
to cost. The cheap ones have short focal
lengths, which makes putting the soldering
iron under them difficult or impossible.
There are other options available: large,
desk-mounted lenses on angle-poise
stands, some with integrated light sources, but again you are limited by a single
magnification factor, and also there are
no options for capturing images to a file.
Despite the limitations, these will also
be expensive, and not suited to kitchentable development.
Instrument review
For us, a primary requirement for the
microscope was the ability to save the
image to a file, specifically for publication
within this magazine. With this in mind
we set a budget of around £100 pounds
(but not below £80) – we wanted to avoid
the obviously cheap end of the market.
It’s difficult picking the good solutions
from the bad by looking at an advert on
the Internet. Prices range from £50 or so
to several hundred – but since we were
‘taking a risk’, we chose to go with one
that looked right, at a reasonable price –
£120 delivered in this case. We searched
through Amazon, eBay and Banggood.
Our choice came from Banggood (Item
ID 1377420 at: http://bit.ly/pe-feb20-ps).
We have made several purchases
through Banggood before; the quality
can be variable, but it is a stable and safe
platform to make purchases on. As safe
as any other Internet purchase, that is!
The instrument is called, ‘HAYEAR
14 Million Pixels Full HD Color Screen
Digital Magnifier Microscope 1 / 2.3
Inch Electron Digital Microscope Image
Sensor With Bracket’. Let’s be clear, this
is not an ‘electron microscope’, digital
or otherwise! This may be a translation
error – perhaps they meant ‘Electronic
Digital Microscope’? It’s advertised as a
14-million-pixel device, but this is sly
marketing – it’s a 2.1-megapixel camera;
the saved image is simply scaled up in
size by software. Sadly, no great surprise
– that’s the standard of honesty we have
become accustomed to when purchasing
on the Internet.
Delivery was a little quicker than the
worst-case delivery stated, so pretty typical for Far-East shipments.
The packaging was excellent, and it
appears to be a nice solid unit with capabilities beyond those of a simple webcam
on a stand. This was a good start. You can
see the device in action in Fig.3
A variety of cables are included: USB
to supply power to the two LED lights in
the base; another USB for camera power
and image upload to a PC; and an HDMI
cable for direct connection to a display.
As the device has a micro SD-Media
card for image storage we set the device
up for the latter configuration. A USB
Practical Electronics | February | 2020
Fig.3. The digital microscope in use; the image is displayed on a large PC monitor.
power supply was provided, but it was
for a US power socket, so we discarded
it and used our own mobile phone charger power brick.
The addition of two light sources on flexible mounts is great; you can easily adjust
both to find those hard-to-spot hidden
dry joints. A variable resistor provides
light intensity control, although with a
poor range of setting – still, good enough.
The 2.1 megapixel image quality is excellent, and the camera does a fine job of
displaying components and solder joints.
Good for PCB work
A key advantage of this microscope is
the gap between the workspace and
the camera; it’s perfectly acceptable for
soldering. It took about an hour to get
comfortable looking at the computer
screen (ie, away from the work surface),
and for short periods of time it is excellent. If we have to spend hours soldering
components, then the Nikon remains the
preferred option – it’s more comfortable
to use, very simple to set up (ie, no setup)
and is of a build quality that means it will
be in use for decades.
The build quality of the Banggood device
is mixed. The electronics, camera and
lights are fine. The rack and pinion provided to raise and lower the camera, less
so. They are metal parts, but of cheap
quality and they frequently stick going up,
which indicates this is not going to last for
many years. That’s not a big concern; this
device is ten-times cheaper than the Nikon
microscope, and it offers many modern
features. The system is modular, so you
can move the camera and lighting to another platform at a later date if required.
The final interesting inclusion is a
remote control. The handset repeats the
functions on the camera, with the main
features being to take a photo to an SD
media card, or adjust the zoom level.
The zoom feature is useful, but it’s no
magic bullet for adjusting image quality.
For that, you need to adjust the camera
height manually. From the highest point
to the lowest, the basic optical zoom
factor ranged from ×3 to ×10 magnification. That’s perfectly acceptable, and
software-controlled zoom can triple that.
In conclusion, was this worth buying?
The answer is, it depends. If you need to
move on from a set of ‘helping hands’,
then you must decide if you need to take
photographs of your board . If not, buy
an old, second-hand PCB microscope for
around £150. If a photograph and visual
clarity for building projects is important,
then this is a great purchase. It’s certainly
a valuable addition to our lab, and you
can expect all future Pic n’ Mix images
of PCBs to come from it!
53
|