siliconchip.com.au Australia’s electronics magazine April 2019 13
SCwith veroboard and similar. All you
need is some wire wrap wire (Kynar),
fine solder and a fine tipped solder-
ing iron.
In the Mailbag section of that is-
sue, Cameron Wedding requested that
a high voltage linear power supply
should be considered as a project. It
is a good idea.
Please consider using two 12V-30V
6A transformers. The tappings could
be switched into and out of the circuit
to provide a broad range of voltage and
current combinations with minimal
power loss and heating.
I enjoyed the 3D printing article
by Dr Maddison in the January 2019
issue of Silicon chip. It is not some-
thing of great interest to me but even
so, it was an excellent overview of the
technology.
I had no idea of the types and ca-
pabilities of 3D printing equipment.
From someone who designed complex
pieces of equipment, there were quite
a number of my designs that could
have been prototyped using 3D print-
ing. However, I must express caution
about the technology.
I have watched a machining station
produce a very intricate part in about
a minute with a resultant cost of about
$5. There is no way that a 3D printer
will match that and I am quite sure the
same would apply to injection mould-
ed parts. Without a doubt, 3D printers
will find a niche in industry but they
are not going to displace some of the
current technologies.
I also liked the article by Jim Rowe
about stepper motors but there are a
few things that he did not mention.
One is the ratings of the motors. Many
of the motors that I have used have
been rated at around 2V and 2.5A. This
voltage is not the driving voltage of
the motor but the maximum DC drop
across each winding. The current rat-
ing is the maximum permitted wind-
ing current.
I have used several supply voltages
with stepper motors from 5V to 24V
but I have seen supplies as high as 80V
used. The reason is speed.
With motors stepping at thousands
of steps per second, the magnetic
fields in the poles must go from zero
to maximum and back to zero in a very
short time and that requires high ap-
plied voltages.
In the earlier days, the current was
limited using constant current drives
or simply resistors but that method is
very wasteful. The efficient method is
to use switchmode type drivers. I have
used the LMD18245T from Nation-
al Semiconductor and the MTD
from Shindengen but now use the Al-
legro driver, A3979 and can recom-
mend it.
The only catch is that the IC has an
exposed die which must be bonded to
the PCB for heatsinking. However, Al-
legro make a 750mA SOIC packaged
driver which would handle most hob-
by applications. It is designated A
and the data sheet has some useful in-
formation about switchmode stepper
motor drivers.
While Jim showed a variety of motor
types (I have used almost all of them),
there is one that is missing. It is a lin-
ear stepper motor. I have two of these
and they were removed from 15-inch
printers of IBM manufacture. I have
never seen them in any other equip-
ment and I keep them as curiosities.
The PicoPi Pro Robot article in the
January 2019 SC is a nice design. It
is still in the class of robots that I re-
fer to as sugar coated but it has a very
redeeming feature and that is the
choice of microcontroller. Both the
PIC16F505 and the PIC16F506 are
mentioned but it is the use of the 505
which I like.
It is a simple microprocessor, like
the good old Z80. It is a good choice
for beginners to learn on. One of its
great features is that it shares a com-
mon pin pattern with quite a few other
microcontrollers.
George Ramsay,
Holland Park, Qld.Origin of the Useless Box
In reading the description of the
“Useless Box” in your December issue
(siliconchip.com.au/Article/11340), I
noticed its similarity to Claude Shan-
non’s “Ultimate Machine”. Maybe I
missed it, but I expected someone to
comment and give Shannon a mention.
Peter Dare,
New Zealand.
Comment: we had not heard of Claude
Shannon or the Ultimate Machine.
This is an idea which has been float-
ing around for a while. According to
Wikipedia, the first “useless box” was
made by Italian artist Bruno Munari
in the 1930s, and the idea was then
picked up by Marvin Minsky of Bell
Labs/MIT in 1952. That was appar-
ently where Claude Shannon, also at
Bell Labs, got the idea.For Wholesale prices
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