Visual programming with XOD
By Julian Edgar
Introducing XOD visual programming for Arduino
I
have a confession to make: the
massive and growing use of programmable microcontrollers in hobby
electronics has largely passed me by.
Why? Well to be honest, I find listings of
code terribly off-putting – one character
in the wrong place and the program
won’t run; and anyway, who wants to
learn lots of arcane instructions before
you can get a microcontroller board to
do even the simplest thing? (OK, lots
of you! But others, like me, just want
to get a quick digital fix!)
Well, in the last few months I’ve
had an epiphany – and it’s all due to
XOD (pronounced ‘zod’). XOD is a free
visual programming software package
for Arduino. There is no code – you
simply place pre-built blocks on the
screen, and then ‘wire’ them together.
If you can understand a simple circuit
diagram, you can program an Arduino in XOD.
I’m in no doubt that an expert code
writer would find many deficiencies
in XOD, but for someone without that
The XOD programming screen. In the main work area is the program (‘sketch’) that’s being
built. Here the LCD programming box has been highlighted – the left-hand lower column
on the screen shows the configurable settings for the LCD and the right-hand column
displays the help file for the LCD.
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background who wants to quickly get
Arduinos doing real-world things,
it’s just wonderful. Furthermore, the
level of support is good. Rather than
hundreds of poor YouTube videos, the
software has an inbuilt tutorial with 42
clear and relevant lessons. These take
you from zero knowledge through to
possessing enough knowledge to build
quite complex control systems. There
is also a user forum that I have found
supportive and helpful.
Finally, XOD allows you to emulate the program on-screen – that is,
you can see how the program will
run, even as you write it. This makes
it far easier to debug your program.
Getting the software
The software can be downloaded
from https://xod.io/downloads/ and
is available for Windows, macOS
and Linux platforms. (If you don’t
want to initially download the desktop version, you can also explore the
software a little by using a browser
version.) Prior to downloading, or
using the browser version of XOD,
you will be required to create an account with your email address and
a password. A reminder – XOD is
completely free, so you don’t get a
version that is incomplete or hamstrung in what it can do.
Installing and running the software
is straightforward; the only issue I had
was specifying the correct Arduino
board when uploading to the board
for the first time. For an Arduino Uno
or clone, select the default ‘Arduino/
Genuino Uno’ option. You might also
find that you need to specify the correct PC communication port.
Practical Electronics | March | 2020
Fig.1. An Arduino Uno board – they’re incredibly cheap, and
with the use of XOD visual programming software, now very
easy to program. You can have projects up and running in
literally minutes.
Note that to use the software, the
Arduino board must be connected
to the USB port of the PC – the USB
connection powers the board. (There
is also an online simulation function
available for XOD, but I have found
it to be a bit erratic.)
Using the software
The first step after downloading XOD
is to do the in-built tutorial. It’s quite
detailed, and if you do all the suggested activities (the tutorials are
done in the actual programming environment), it will take some hours.
That said, after the first ten lessons,
you’ll have enough information to
LED
Fig.3. The DFRobot 1602 LCD Keypad Shield module plugged
into the Arduino Uno board. The Uno is programmed with the XOD
software discussed in this article and the display is showing the
current temperature and the setpoint at which the alarm LED lights.
start programming. You can return
to the tutorial at any time by going
to: Help > Open Tutorial Project. I
also found this page helpful: https://
dronebotworkshop.com/gettingstarted-with-xod/
The hardware
In this example, I’ll use:
Arduino Uno, for example the
board shown in Fig.1
Microchip MCP9700 temperature
sensor IC
LED with suitable dropping resistor
10kΩ potentiometer
DFRobot 1602 LCD Keypad Shield
module (Fig.3).
Anode (a)
Dropping resistor
approx 470Ω to 1kΩ
Cathode (k)
7
6
5
4
3
2
1
0
SCL
SDA
AREF
GND
13
12
11
10
9
8
MCP9700
DIGITAL
POWER
ANALOG IN
5V
RES
3.3V
5V
GND
GND
VIN
A0
A1
A2
A3
A4
A5
UNO
1 2
3
VDD
GND
VOUT
MCP9700
10kΩ
1 2
3
Fig.2. The initial set up for the Arduino board temperature alarm using an MCP9700 sensor
and LED with dropping (current-limiting) resistor. (LCD shield not yet added.)
Practical Electronics | March | 2020
Let’s start with the temperature sensor. Connect the appropriate pins (see
Fig.2) from the sensor to the on-board
5V and ground, and the output to port
A5 (analogue 5). (Note: all connections are labelled on the board.)
Connect the LED between pins D13
and ground. (To speed things up, I
buy LEDs pre-wired with a resistor
for 12V use. They’re still plenty bright
enough, even when working off 5V.)
Ensure correct polarity.
Finally, connect the pot across the
5V and ground terminals, with its
wiper (middle terminal) connected to
port A4. You should now have what
is shown in Fig.2. (We will get to the
LCD shield later.)
Writing a program
Select File > New Project – you will be
then confronted with a largely blank
screen. This is your working area
where you will build the program. On
the far left and far right are two narrow
columns – these display information
that helps you as you proceed.
Let’s make a temperature alarm,
and to make it trickier, let’s average
the temperature reading over about
five seconds and condition the sensor
output so we’re working in degrees
Celsius (°C). We’ll then add a pot
input to adjust the setpoint temperature, and then an LCD to show both
setpoint and real-time temperatures.
Sound hard? It isn’t!
Functional building blocks
You can see from the pictures in this
article that the program is built from
functional blocks (called ‘nodes’) –
but where are they? Double clicking
in the main work area will bring up a
‘search nodes’ box. We want to start the
programming by having an analogue
61
Fig.4. Adding
the first XOD
block – an
‘analog-sensor’
functional box.
sensor (the temperature sensor) input
to the Arduino board. Typing ‘analog’
into the search box brings up xod/
common-hardware/analog-sensor.
Select this by double clicking on it. A
functional box called analog-sensor
will then be added to the main work
area – see Fig.4.
Clicking on this box brings up information in the two screen columns.
At right, each label on the functional
box is explained, while at left these
can be user-configured. The labels
on this first box are:
PORT – the analogue port that is going to be used for this input on the
Arduino board. Change it to A5.
UPD – how the input is updated. The
options are ‘never’, ‘on boot’ and
‘continuously’. Set it to ‘continuously’ – shown on the box as ‘loop’.
VALUE – the output value, configured
automatically to be in the range 0-1.
DONE – outputs a pulse when the
reading is done (we don’t use this).
We can re-label the box to read something other than analog-sensor
– and now, using the column at left,
label it Input temp.
So we’ve now added an analogue
input on port A5 that is continuously
updated and is labelled in a way we
can immediately understand.
Fig.6. Adding blocks to display the sensed
temperature in °C.
see the real-time working of the program, as shown in Fig.5.
By heating and cooling the temperature sensor you should now see the
value in the watch box changing – we
have an input!
Hmm, but there is also an issue –
at room temperature, the output of
the sensor is showing 0.14 – not a
‘real’ temperature reading. We need
to convert the reading to degrees Celsius, and with this sensor that means
62
multiplying this reading by 500 and
subtracting 50. So how do we do that?
Processing the input values
Double-clicking in the workspace and
searching under ‘multiply’ brings up
xod/core/multiply that we then
select. We connect the IN1 of the
multiply box to the VAL output of
the input temperature box, and using
the left-hand column on the screen,
change the IN2 value to 500.
We then add a xod/core/subtract
box and subtract 50. (Well, as you can
see here, I actually used 48 – that offset giving better accuracy with the
particular temp sensor I was using.)
We can then add another watch box
to the output of the subtract box and
upload the program in debug mode
to the board. You should then see the
reading showing in degrees Celsius,
as shown in Fig.6.
Creating an input
But is our input actually reading anything? Double-click the work area
and type debug and a series of options pops up – select xod/debug/
watch and connect this block to the
output (VAL) of the Input temp block.
Upload the program to the board by
pressing the ‘bug’ symbol at bottom
right of the screen. This loads the program in debug form – you can then
Fig.5. Adding a watch box and connecting it to the Input temp block.
Fig.8. A greater box enables the system
alarm to be added. The true/false box
lets you see if the alarm is activated.
Fig.7. Using a user-generated average
function to generate five-second averages
of the temperature readings.
Data processing
Now we want to average the temperature reading; eg, over five seconds. But
if you double-click on the work area
and start typing ‘average’, you’ll find
you don’t get any result – there is no
‘averaging’ block available as standard.
Practical Electronics | March | 2020
Upload the program in debug mode. Now the LED
lights when the measured temperature is above 25°C,
averaged over about five seconds. (You’ll also notice that
an on-board LED lights too – it’s also connected to D13.)
External pot input
In the program’s current format, the set-point temperature
of the alarm is typed into the software. But what if we
wanted to adjust the setpoint with the external pot? As
shown here, doing this takes only moments. Note that we
are using port A4 for the pot input, and again, we multiply its output by 500 (no subtraction necessary) and then
average the output. Here the set-point is 26.47°C. (Would
you like to round this number? If so, find the xod/math/
round box and add it.) See right-hand side of Fig.9.
Connecting an LCD display
Now, what about showing on an LCD screen both the setpoint and monitored temperature? But I must be honest.
There is a potential hardware hurdle here – and that is
that LCD modules have a wide variety of different pinouts. The default LCD 16 × 2 programming block in the
XOD software was not a match for the DFRobot 1602
LCD Keypad Shield module I used – that is, it wasn’t
‘plug-in compatible’ so I had to make some port changes. Doing this meant looking up the data sheet for the
LCD module and changing the designated ports on the
XOD LCD block (covered in a minute) to match the functions of the different pins. In the case of the DFRobot
LCD this comprised:
Fig.9. Here we add blocks to: a) enable the Arduino to light the LED
when the alarm is triggered; and b) use the pot to adjust the setpoint.
However, one of the advantages of the XOD system is that users can upload their own useful blocks for others to use. These
can be found on the XOD website under ‘libraries’. By going
to File > Add Library and typing in the library name as shown
on the website, these extra blocks can be added. average is
one of them – it’s under ‘gst/average/average’. This box has six
labels, but we’re interested in only three – in, out and step.
Click and drag a line from the output value of the subtract
box to IN on the average block. Change STEP to 500 and INC
to Continuously (shown on the box as LOOP). Now we’re averaging the output of our temperature sensor over about five
seconds. But will it work? Add a watch box to the output of
the average box, upload the program in debug mode to the
board, and then check that the temperature reading is now averaged over a period. (Fig.7)
Adding the alarm
Now we’ll add the alarm part of the program. Select a xod/
core/greater box and link IN1 to the output of the average
box. Change IN2 to 25 (as in, 25°C). Add a watch box to the output of the greater box. (See Fig.8.)
Upload the program in debug form and check that the watch
box changes from false to true when the temperature of the
sensor is over 25°C. (Note how the watch box can show both
values (numbers) and logic (true/false) states.).
Driving the LED
The next step is to light an LED when the alarm is triggered.
Add a xod/common-hardware/led box to the screen – searching under ‘led’ will bring this box up. Change its port to D13
and connect its LUM pin to the output of the greater box.
(See lower left, Fig.9.)
Practical Electronics | March | 2020
LCD pin
RS
EN
D4
D5
D6
D7
Arduino port
D8
D9
D4
D5
D6
D7
To add the LCD shield, first remove the existing temperature sensor, LED and pot connections. Then plug in the
LCD shield, ensuring it is positioned as far towards the
end of the Arduino board as possible. With this done,
we now need to reconnect the pot and temperature sensor inputs using the analog inputs pins on the front
of the shield. The LED output also needs to be moved.
The port numbers remain the same, so this takes only
moments – although you will need to change from male
to female connectors.
The text-lcd-parallel-16x2 box is then added. L1 refers to line 1, and L2 to line 2 on the display;
each is a separately addressable (see Fig.10). Line 1 is
then linked to the averaged input temperature via a
xod/core/concat box that is used to display the word
‘Current:’ and the numerical temperature reading. Line 2
uses a similar concat box to display the word Setpoint:
and the pot’s averaged output. The changed program is
then uploaded in debug mode, and you should see the
complete system working. (If the LCD does not show anything, try adjusting the on-board contrast pot.)
Conclusion
And there we have it! We have built a digital over-temperature warning system that lights an LED when the
setpoint temperature is exceeded and displays on an
LCD the current temperature and the setpoint temperature. Yes, it’s a basic system, but it needed no code
and was quick and easy to put together.
63
Now consider how easily it could
be extended or altered – for example:
Changing the temperature averaging time requires altering only one
number in the software
Fine-tuning the accuracy of the
temperature sensor is as easy as
changing the offset number
Adding hysteresis requires just
one more programming box (a
hysteresis block is available in the
Libraries)
Altering what is displayed on the
LCD (eg, displaying the temperature averaging time rather than
setpoint) is as easy as drawing a
new connecting line and changing
the text label
Comparing the difference between
two temperatures requires only the
addition of another temperature sensor and a few boxes of programming.
And the XOD software? The proof of
the pudding is in the eating – in just
this story we’ve not only introduced
the programming software, but also
managed to build a complete project!
What next?
I hope this piece inspired you to try
XOD with an Arduino – there will be
plenty more XOD-based projects in
upcoming issues to tempt newbies
into discovering the power of digital control.
XOD files
The XOD file discussed in this
article can be downloaded
from the March 2020 page of
the PE website.
Fig.10. Adding the DFRobot 1602 LCD Keypad
Shield module completes the alarm project. (Note:
this image only shows the lower section of the blocks;
the top section is identical to the top two rows in
Fig.9.) Pin compatibility issues meant this was the
only complex stage of the project – but XOD took it in
its stride, and the LCD shield works well – see Fig.3.
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Practical Electronics | March | 2020
