Visual programming with XOD
By Julian Edgar
Light Column Thermometer
P
icture the scene. You have some guests at
your house and their eyes are attracted to a small
device sitting on a shelf. The base is clear, and an
electronics board can be seen, together with two projecting
tubes, each pointing upwards. Sometimes the tubes fill
with light, their entire columns illuminated. There seems
to be a pattern in the way the tubes flash – but what is it?
First the two tubes light up together, one white and one
blue. They flash for a few moments and then the white
tube goes dark, just the blue tube continues to flash. Both
then turn off, and the cycle starts again. It’s obviously not
random flashing, but what is it?
This time the guests count the flashes, and realise the
white and blue tubes flash twice, and then the blue tube
flashes three times. But no – this time around, the blue
tube flashed four times! So, what is it? Realisation dawns
– it’s a thermometer, in this example reading 23°C and
24°C, respectively.
This is a fun project – an indoor thermometer that displays the temperature in a unique way. It’s cheap, very
easy to construct and almost as easy to customise.
Cheap? The Light Column Thermometer uses an Arduino Uno board (clones now cost under £5 delivered),
two clear plastic Uno enclosures (£2 each) and a handful
of low-cost components. The light columns are recycled
ballpoint pens illuminated by bright LEDs.
Easy to construct? Soldering will take you only moments
and other than that, it’s just a case of drilling some holes
and screwing and gluing parts together.
Customisable? The program (sketch) for the Uno is
written in XOD visual programming language. XOD (pronounced ‘Zod’) was introduced in the March 2020 issue
of PE and is completely free to use. Unlike lines of code
that often appear impenetrable, XOD is easy to understand
and hence is easy to modify. If you wish, it will take you
literally moments to alter the flash duration, flash fade
speed – or even how often the cycle repeats. And you
don’t need to have white and blue flashing columns – just
use whatever colour LEDs you prefer.
Building
The Light Column Thermometer uses the following parts,
with the specific ones I used shown in brackets.
Arduino Uno (eBay cheap clone – *see note below)
Plastic Uno box (laser cut – I used two, eBay)
Two pre-wired 5mm LEDs (blue and white, already fitted with dropping resistors – Banggood)
LM35 DZ temperature sensor (eBay)
Two discarded clear ballpoint pen barrels (salvaged)
Assorted screws, nuts and spacers (in my parts box)
The Light Column Thermometer displays the temperature by
using two illuminated plastic tubes. One tube shows ‘tens’
and the other ‘units’, with the number of flashes indicating the
appropriate values.
Practical Electronics | January | 2021
*Note: Some low-cost Uno modules do have one ‘wrinkle’. Many use a non-standard USB communications
chip, which if you are to communicate with it, needs
a new PC driver. Some users report that Windows can
find the driver by an automatic on-line search, but I had
to download the driver from: www.wch.cn/downloads/
CH341SER_EXE.html
63
If you are new to using Arduinos,
perhaps initially stick with ‘official’
products – they don’t need new drivers.
The enclosure uses the baseplates
of two laser-cut boxes widely sold for
use with the Uno. I used two baseplates (as opposed to the normal top
and bottom parts) so that the top plate
didn’t have cut-outs in it. These cutouts are provided to gain access to
the pins, but I spaced the top and
bottom of the enclosure further apart
than usual (thus giving internal access
to the pins) and so I didn’t need the
cut-outs. Of course, you can use just
one box if you don’t mind the slots
in the top panel.
The top and bottom panels are
spaced 20mm apart using plastic
stand-offs, and the Uno is bolted to the
baseplate via screws, plastic washers
and nuts.
All the holes in the enclosure panels for mounting are drilled out to
3mm diameter, allowing the use of
normal-sized spacers and screws.
(As standard, these holes appear to
be 2.5mm) The side and end plates
of the enclosure are not used.
The light columns are, as described,
salvaged ballpoint pen barrels. Pick
a transparent design that has an interesting shape, preferably without
writing on it. Different barrels will
give different lighting effects; test the
result by shining a 5mm LED down
the end of the tube.
LED
SCL
SDA
AREF
GND
13
12
11
10
9
8
Anode (a)
LED
Use prewired LEDs that include
dropping resistors, or add your
own resistors (approx 470Ω to
1kΩ) to standard LEDs.
7
6
5
4
3
2
1
0
LED
Cathode (k)
An Arduino Uno and two low-cost commercially available enclosures form the main
components of the project. The upright columns are salvaged ballpoint pen bodies.
DIGITAL
UNO
ANALOG IN
A0
A1
A2
A3
A4
A5
5V
RES
3.3V
5V
GND
GND
VIN
POWER
LM35DZ
LM35DZ
1 2
1 2
VCC
VOUT
3
GND
3
Fig.1. Connection diagram for the Arduino Uno, together with the pin-outs for the two LEDs
and the LM35DZ temperature sensor. Its 5V supply is taken from the Arduino. Note: you can
use LEDs prewired with dropper resistors, or ordinary LEDs and choose your own resistor.
64
The end of the pen barrels I used
had a short length of exposed plastic thread. Two holes just undersize
of this thread diameter were drilled
in the top panel and then the plastic
pen barrels could be screwed into
the holes. A little cyanoacrylate glue
(‘superglue’) was used to secure them
into place. The pre-wired 5mm LEDs
were glued into the ends of the tubes.
Wiring
Refer to Fig.1 for the pinout of the
LM35 temperature sensor. Port A0 is
used for the signal, and the sensor’s
5V and ground connections can be
made close by on the Uno (all Uno
ports are labelled). I used header
pins and soldered the LM35 straight
to these. Ensure that the signal wire
cannot touch the ground connection.
The LEDs were wired between
ground and ports D3 and D5, again
using cut-off header pins. Remember the correct polarity for the LEDs
– positives/anodes, to the ports; negatives/cathodes to ground.
Power to the board can be supplied
via the DC socket (5-12V) or USB input.
Software
To upload the program (sketch) to
the Uno you will have first needed to
install XOD on your PC (see https://
xod.io/downloads/ – remember, it’s
free after you register). You will also
need to download the Light Column
Practical Electronics | January | 2021
Thermometer sketch from the January 2021 page of the PE website.
(Note that depending on whether
you have used XOD previously,
the software might prompt you to
do some further downloading of
extra libraries.)
Refer now to Fig.2. The beauty of XOD is that’s it very easy to
understand. In the red box (top of
diagram) we have the input from
the temperature sensor, constantly
read through Analog Port A0. This
value is multiplied by 500, averaged and then rounded. (The ‘live’
temperature is shown in the green
‘watch’ node, that operates when
the sketch is uploaded to the Uno
in ‘debug’ mode.
We now need to extract from
this number the ‘tens’ and ‘units’
– see the green box. Dividing the
value by 10 and then using a ‘floor’
node does this for the ‘tens’. Now,
what about the ‘units’? The ‘modulo’ node does this by calculating
the remainder of (again) dividing
our temperature value by ten. Two
‘watch’ nodes allow us to see these
outputs live.
Let’s do the white box next –
the flashing shows the number
of ‘units’. Our ‘units’ number is
fed to a ‘flip-n-times’ node. This
node flashes the LED output the
required number of times, and also
sets the flash rate and duty cycle –
in this case, 0.2 seconds ‘on’ and
0.5 seconds ‘off’. The ‘gate’, ‘not’
and ‘equal’ nodes then prevent
an output if the ‘units’ number is
zero. (Otherwise, the ‘flip-n-times’
node outputs one flash, even with
a 0 input.) We then feed the output
through an ‘or’ node (more on this
in a moment) and then through a
‘fade’ node. The fade node gives a
gradual (although still pretty fast)
rise and fall in LED brightness with
each flash.
Now, what about the ‘tens’? The
tricky part here is twofold: first,
the ‘units’ column needs to flash
at the same time as the ‘tens’ column when ‘tens’ are being shown,
and second, the ‘units’ can’t start to
flash until the ‘tens’ have finished
their sequence.
Flashing the ‘units’ LED when
the ‘tens’ LED is flashing is
achieved by the ‘or’ node. But what
about not starting the ‘units’ until
the ‘tens’ are done? This is done
Fig.2. The Arduino sketch for the Light
Column Thermometer is written in XOD
visual programming language. The sketch is
fully explained in the main text, but in brief,
Practical Electronics | January | 2021
the red box shows the temperature input
nodes, the yellow box extracts the ‘tens’
and ‘units’ from the reading, the white box
flashes the LED for the ‘units’ reading, the
brown box flashes the LED for the ‘tens’
reading, the yellow box starts the ‘units’
only after the ‘tens’ have finished, and the
blue box sets the cycle time.
65
‘tens’ flashes and four ‘units’ flashes). Each flash takes 0.7
seconds (0.5 off and 0.2 on), giving a total of 4.2 seconds.
Add to that the one-second delay between the ‘tens’ finishing flashing and the ‘units’ starting, and we have 5.2
seconds for the sequence. Since the clock resets at (in
this example) six seconds, we have a 0.8 second delay
at the end of the cycle before it starts again. Taking this
approach means the cycle time adapts to the required
number of flashes.
As with all XOD sketches, this one is easily customised.
For example, if you wanted the cycle time to be longer,
you could put another ‘add’ node in above the ‘clock’ and
add a further (say) five seconds to the cycle time.
Note that as configured, the thermometer cannot show
negative temperatures, nor degrees Fahrenheit. (Both of
these are quite possible, though. For example, XOD even
has available a direct units conversion node for Celsius/
Fahrenheit – you might want to try adding it to the sketch.)
Spacers are used to hold the two parts of the enclosure 20mm
apart. This gives enough room for the wiring of the temperature
sensor and two LEDs to be placed within the enclosure.
by the contents of the yellow box – that registers when
the ‘tens’ have finished, adds a delay of one second, and
then starts the ‘units’ flashing.
The brown box comprises the logic for the ‘tens’ flasher; it uses the same approach as for the ‘units’.
The blue box starts the cycle. It does this by adding the
‘tens’ and ‘units’ numbers together to gain the total required number of flashes. In this example that is six (two
Conclusion
I find the Light Column Thermometer fascinating to watch.
It can be seen from across the other side of the room, and
reading it is oddly relaxing – perhaps because you have
to pause and watch, rather than just glance and run. It’s
also an ideal project with which to discover the fascinating world of XOD.
XOD files
The XOD file discussed in this article can be downloaded
from the January 2021 page of the PE website.
See PE March 2020 for an introduction to using XOD.
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