Max’s Cool Beans
By Max the Magnificent
Flashing LEDs and other engineering temptations – Part 34
I
n my previous column (PE,
Rotate that!
signal. In fact, if you don’t need to read
the encoder at full resolution you can
make things even simpler. I suspect this
is why some of the encoders you looked
at give two or four transitions per click. If
you only need quarter resolution for example, you can just look for Low->High
transitions of signal A and use signal B to
tell you the rotation direction. This type
of approach is simple to implement and
doesn’t need any information about the
previous state of the encoder or where
the ‘click’ points are. I use this approach
in Cyclepong.’
Unfortunately, as I pen these words,
everything feels a little ‘fluffy around
the edges’ on the cognitive processing
front. I just got back from a visit to my
One such example is Cyclepong (do see
this: https://bit.ly/3RYRQG8), which is an
update of the classic arcade game Pong
(https://en.wikipedia.org/wiki/Pong)
using bikes as the controllers. Billed
as ‘Bringing two of humanities greatest
inventions together,’ Cyclepong (Fig.1)
also promises to ‘Build thighs of steel
(weather permitting).’ At the time of this
writing, Cyclepong is on show at Novelty Automation in London (https://bit.
ly/3Vo8Vfw). Iain’s current project is an
electromechanical version of the classic
Lunar Lander computer game (https://bit.
ly/3ESSnX4), but we digress...
In his email, Iain spake as follows: ‘Hi
Max, Re your piece in PE Nov 22 on the
work you and Joe Farr are doing with
quadrature encoders. There is a ‘trick’
to decoding them that used to be well
known but seems to have been largely
forgotten more recently. Instead of tracking the state of the encoder and determining which signal is ‘leading’ to work
out the direction of rotation, you can find
the direction from the signal state when
a signal transition takes place. For example, looking at Fig.4 in your piece. If
A goes from Low->High when B is low
then this is always a CW step. If A goes
from Low->High when B is high this is
always an ACW step. You can build a
truth table for all the possible combinations (as you would expect it’s very symmetrical) and immediately know the direction of rotation from the direction of
the transition and the state of the other
Fig.1. Cyclepong: experience man and machine in perfect harmony.
November 2022), I waxed eloquently
on the topic of rotary encoders. Following this, I received an email from
PE community member Iain Sharp who
hails from Nottingham, which is where
my dad was raised. Iain tells me that
his day-job involves supporting the
development of some very cutting-edge
technology, but that his role these days
is mostly focused on project management and budget issues, so he spends
his spare time doing interesting (and
diverse) hands-on projects that remind
him why he got into engineering in
the first place.
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doctor who tells me I tested positive for
Covid. I can’t believe it, I had it only
three months ago, I’m too young for all
this excitement. They’ve put me on antivirals (Q: ‘Do you have the antivirals?’ A:
‘No, I always walk this way!’) so I hope
to return to full cognitive capacity in a
few days’ time, which is when I’ll peruse
and ponder Iain’s proposal in more depth
and give it the consideration it deserves.
Having said this, my brain is still ticktocking away in the background (albeit
skipping the occasional tick or tock),
and it’s trying to decide if Iain’s simplified scheme works while still addressing
the problem of noisy signals caused by
switch bounce. Another issue Joe and I
wish to address is preventing the system
Practical Electronics | December | 2022
VDD
Make
1
Break
NO
0
NO
1
COM
NC
SPDT Switch
Break
Make
NC
0
First 0 on NO
Fig.2. Switch bounce on an SPDT switch.
a)
b)
c)
d)
Practical Electronics | December | 2022
First 0 on NC
from getting confused when you are rotating the knob quickly and you turn it
halfway past the final ‘click’ and then
return it to the final ‘click’ location. This
will also require some pondering in the
context of Iain’s suggestions.
A tight squeeze
Speaking of switch bounce... were you by
any chance wondering how I spent last
Saturday? You were! Well, this is your
lucky day because I’m in the mood to
share. In previous columns, we’ve talked
about the problem with switch bounce for
single-pole, single-throw (SPST) switches
(PE, March 2022) and single-pole, doublethrow (SPDT) switches (PE, April 2022).
It’s the bounce on the latter type which
interests us here (Fig.2). Remember that
NO stands for ‘normally open’ and NC
stands for ‘normally closed.’
The last time we talked about this, we
looked at how to remove this bounce
using two back-to-back NAND gates.
For the purpose of these discussions, we
are focused on the small breakout board
(BOB) that LogiSwitch uses to debounce
SPDT microswitches and small pushbutton switches (Fig.3a). This board is
0.45-inch wide and 0.5-inch tall. On the
top side, there’s a small LogiSwitch IC,
a capacitor, and (in the lower middle of
the board) a field-effect transistor (FET),
which protects you if you apply the voltage the wrong way round. On the bottom
of the board are three large pads. From
top to bottom (in this image) they are
GND, NO (fed from the switch’s normally open terminal), and NC (fed from
the switch’s normally closed terminal).
The five small pads on the edge of the
BOB are V+, NH (normally high), NL/
HS (normally low with handshake), TG
(toggle) and GND. When the switch is in
its inactive state, the NH output from the
BOB is high (logic 1). When the switch is
activated (which we take to be the first 0
on NO), the NH signal goes low (logic 0).
When the switch is deactivated (which
we take to be the first 0 on NC), the NH
signal returns to its high state.
The NL/HS signal presents the opposite
values to the NH signal with an added
twist. When the switch is activated and
Fig.3. Inserting a BOB into a very small
space. Top to bottom: a) LogiSwitch
breakout boards (BOBs) used to
debounce SPDT microswitches and small
pushbutton switches; b) 8108 lever-arm
limit switch with adjustable roller – my
target for the LogiSwitch BOB; c) There’s
not a lot of spare space inside the limit
switch. I had to file down some plastic to
make everything fit (the surfaces marked
red); and d) connecting it all up.
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Next, I connected the NC and NO
terminals on the far side of the switch
together to give me a common (COM)
signal and connected this to the GND
pad on the BOB. I also connected the
NC and NO terminals on the nearside
of the switch to the corresponding pads
on the BOB (Fig.3d).
Finally, I ran a little program on an
Arduino Uno to make sure everything
worked as expected before sealing the
switch up again (Fig.4). Oh, did I forget
to mention that I then had to do all of
this for another 14 switches (sob).
Eek! Zeke!
Fig.4 Checking the LogiSwitch BOB works in the limit switch.
the NL/HS signal goes high, the program
in the microcontroller that’s monitoring and using this signal can change its
input to an output, pull the signal low
for 5µs, and then return it to being an
input again. The LogiSwitch IC will understand this to be an acknowledgement
that the switch event has been seen and
it will take over pulling this signal low.
This saves you having to set a flag in your
code to say when you are waiting for the
switch to go inactive. Last, but not least,
the TG signal starts off in a high state.
Every time the switch is activated, the
TG signal toggles to its opposite state.
My mission was to insert this BOB into
an 8108 lever-arm limit switch with adjustable roller (Fig.3b). These are wonderful devices, but it has to be acknowledged that there’s not a lot of spare space
inside (Fig.3c). What is inside is four individual terminals. The two on the lefthand side of this image are marked ‘NO’,
while the two on the right are marked
‘NC’. When the switch is in its deactivated state, a small bar connects the two
NC terminals. When the switch is activated, this bar moves, disconnecting the
two NC terminals and connecting the
two NO terminals.
Observe the clear plastic piece that
holds everything in place. The blue
outer shell sits on top of this without
any gap whatsoever. I started by covering the internals with painter’s masking tape to stop dust getting anywhere
it shouldn’t. I then used a small file to
make a wire-sized groove between the two
halves of the clear plastic (the red lines
shown on the left). There are ‘steps’ in
the clear plastic on the right (on the far
side, middle, and nearside pieces sticking out). I also filed half of the middle
step down further to make room for the
FET on that side of the BOB (the red
lines shown on the right).
One of the things I’ve been meaning to
talk to you about is an amazing 11-yearold kid called Zeke. I was first introduced to Zeke and his dad Eric a couple
of months ago (Fig.5). In this image we
see them holding a circuit board Zeke
designed using AWR Microwave Office
software from Cadence Design Systems
(Zeke is the one on the left).
There’s so much to tell here but (as
always) so little time to tell it. In a
crunchy nutshell, Zeke has been interested in science and technology since
he was about one and a half years old
when Eric took a piece of wood and attached a small incandescent light bulb,
a battery holder, and a knife switch of
the type favored by Igor and Frankenstein (‘It’s alive! It’s alive!’). Zeke carried that little creation around with him
everywhere, turning it on and off and
chanting ‘switch, battery, light bulb…
switch, battery, light bulb…’
When he was eight, Zeke informed his
parents that he wanted to communicate
with the astronauts and cosmonauts on
the international space station (ISS). If
I’d said this to my dad, he would have
patted me on the head and wished me
Left-right: Fig.5. Budding electronic engineer Zeke, with his dad Eric, showing a PCB he designed; Fig.6. Zeke with his first ham radio;
and Fig.7. Zeke working on his 10-foot helical antenna.
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Practical Electronics | December | 2022
luck. By comparison, Eric told Zeke that
in order to do this he would have to a)
get his ham radio license and b) have a
suitable radio system.
Just to make sure we’re all tap-dancing to the same skirl of the bagpipes, the
term ‘ham radio’ (a.k.a. amateur radio)
refers to the use of the radio frequency
spectrum for the purposes of non-commercial exchange of messages, wireless
experimentation, self-training, private
recreation, radio sport, contesting and
emergency communications.
Thus, a few weeks later, Zeke, Eric,
and Zeke’s grandfather Mark attended
a ham radio class together, following
which they took their ham Technician
exam. Eric and Mark passed first time,
but Zeke failed. It took Zeke a couple
of months studying and two more tries
before he also got his Technician license
(he now has his General license) and his
own KJ7NLL call sign, at which point
his grandmother, ‘Bobbi,’ presented him
with his first ham radio (Fig.6).
Eric told me that the very first time
Zeke used his radio, someone immediately responded to his young voice
saying, ‘Who is this and whose radio
and call sign are you using?’ Eric says
that Zeke firmly responded, ‘This is my
radio and my call sign!’
The funny things is that when Zeke is
talking to me, it’s obvious that he’s worried about leaving me behind, so every
time he drops an engineering acronym
like SSB into the conversation, he will
pause and then say, ‘that stands for single-sideband’ (I feel so old).
After looking into several different techniques (one of his back-burner projects is
to create his own phased array antenna),
Zeke opted to build a 10-foot-long helical
antenna (Fig.7). Not shown here is the
chicken wire reflector Zeke has attached
to one end of the antenna. This results
in the bulk of the radiation coming out
of the other end, thereby significantly
boosting the range of the antenna.
Via the ham network, Zeke acquired
two large rotors to control the azimuth
and elevation of his antenna (azimuth
defines the direction to face; elevation
tells you how high up in the sky to look).
Zeke is currently working with some software he picked up from someone on the
internet. This software runs on his PC.
You tell it what satellite (including the
ISS) you want to track and if feeds you
a constant stream of azimuth and elevation values. I will keep you updated as
to Zeke’s progress in future columns.
What’s it all about?
I’m currently thinking about the 1966
British comedy-drama Alfie starring
Michael Caine as handsome Cockney
Alfred Elkins. The title song Alfie was
sung over the film’s closing credits. I now
Practical Electronics | December | 2022
have the first line of the lyrics ‘What’s
it all about, Alfie?’ rattling around my
poor old noggin.
‘Why is that?’ You ask. I shall elucidate and explicate (don’t worry, I’m
a professional). I recently received a
letter from a distraught mother saying
that her 6-year-old son, Alfie, told her
that he wanted a pack of nanobots for
Christmas. After explaining what nanobots are, he told her that he could put
them in a barrel, add some chemicals,
stir things up, and then sit back and wait
for them to build him a supercomputer.
When his mom told Alfie that this was
beyond the bounds of today’s technology, he pointed to the relevant portion of
my book, Bebop to the Boolean Boogie:
An unconventional Guide to Electronics (https://amzn.to/3s15Nc6), which
she had bought for him a few weeks
earlier. Unfortunately, young Alfie had
missed the part where I said this type
of technology was something we might
expect to be talking about in the 2050
edition of the book.
Alfie’s mom asked if I had any suggestions to keep his mind occupied. I
suggested that he read The Chronicles of
Narnia and the Magic Treehouse books,
both of which I think are great for kids of
all ages. She replied that Alfie’s 4-yearold brother Eddie loved reading those
books, but that Alfie himself would rather
be reading about things like logic gates,
p-type and n-type silicon and field-effect transistors. She also said, ‘I told
him once that most grownups prefer to
read stories for fun, not textbooks, and
he looked at me with incredible skepticism, bordering on full disbelief.’
Fortunately, I still had a couple of
tricks up my sleeves. A couple of years
ago, two former teachers, Paul and Alyssa
Boswell, created an awesome marblepowered computer called the Turing
Tumble (https://bit.ly/3TdIPKY). They
launched it as a Kickstarter project,
and it went gangbusters. This comes
with lots of puzzles that I’m sure will
keep Alfie busy (I have one here in my
office and it certainly keeps me occupied). The second, even more awesome,
thing is the latest and greatest offering
from Paul and Alyssa – a mechanical
implementation of electronic components and systems called Spintronics
(https://bit.ly/3s0IoHW). The first production run is currently on the high
seas heading our way (they discovered a
problem with the mechanical resistors if
they were transported via airplane (the
lower atmospheric pressure caused the
silicone gel to leak out).
Suffice it to say that hearing about
these two offerings made Alfie’s longsuffering mother very happy indeed.
Open circuits
I’m really bad when it comes to remembering names and faces. This problem
is only exacerbated by the fact that I’ve
spoken at so many conferences. You’d
be amazed how many people email me
to say something like, ‘I saw your presentation at the XYZ conference in the
year of the fruit bat – I was the one who
asked the question about reverberating
foodle valves’ (or words to that effect),
to which I usually reply, ‘That was you?’
The reason I mention this is that I
just received an email from Philip Freidin, who hails from Silicon Valley and
who started off by saying, ‘You probably
don’t remember me, but we met a few
years ago at an Embedded Systems Conference (ESC) – in 2015, I think – and
chatted for about an hour. I showed you
OSHChip, a 32-bit ARM CPU + Bluetooth radio packaged as a 16 pin DIP.’
The funny thing is that I do remember
this meeting.
Philip went on to say, ‘This email has
nothing to do with any of that.’ (This
brought a smile to my face because it’s
the sort of thing I might say myself.)
It turned out that the reason for Philip’s email was that two of his friends,
Windell Oskay and Eric Schlaepfer, are
poised to publish a book called Open
Circuits (https://amzn.to/3CzWZ1P),
which should hit the streets around the
beginning of November 2022 (which is
now as you read these words).
This book does not require any indepth electronics knowledge and I think
it will be of interest to both engineers
and non-engineers alike. Basically, it
contains a lot of gorgeous photographs
showing the insides of electronic components. You can download a free PDF
of Chapter 1: Passive Components from
the publisher, No Starch Press (https://
bit.ly/3VyHS1i).
I LOVE this book. My wife (Gina the
Gorgeous) tells me that she never knows
what to get me for Christmas. Well, safe
to say that Open Circuits is now at the
top of my wish list.
I’m afraid that’s all we have time for
in this column. As always, I look forward to receiving your captivating comments and insightful questions. Until
next time, have a good one!
Cool bean Max Maxfield (Hawaiian shirt, on the right) is emperor
of all he surveys at CliveMaxfield.com – the go-to site for the
latest and greatest in technological geekdom.
Comments or questions? Email Max at: max<at>CliveMaxfield.com
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