Learning to code Part 4

CCITE
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innovative organisations committed to the improvement
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The Centre for Innovation in Technological Education in Cambridge http://ccite.org
Learning to code - with a purpose Part 4
Adrian Oldknow
March 2015
[email protected]
15. K’Nex and control: In part 1 I showed some Technical LEGO being used as a vehicle for the Crumble
controller. In part 3 I showed a picture of my TI graphical calculator used to control a Mars buggy made from
Meccano. The popular K'Nex construction kits make a cheaper alternative from which to build the chassis
for robot vehicles. A good source of these is the UK branch of the K’Nex User Group:
http://www.knexusergroup.org.uk/acatalog/knex-shop.html?region=uk. Their starter kit for control costs £143 and comes with
a cut down version of the Data Harvest `FlowGo’ system called `Learn&Go’ together with 2 motors, 2 LEDs
and a buzzer. What you don’t get are any inputs, or any form of computer interaction. So all you can do is
control the outputs, and program them with button pushes like the Mindsets IQ4 in section 12 of Part 2.
Compared with LEGO WeDo this is rather a disappointing introduction.
The fuller version costs £239 and includes inputs and computer control via FlowGo:
http://www.knexusergroup.org.uk/acatalog/info_K79017PK.html. A budget alternative is to buy the very cheap `K’Nex
Dancing Robot’ kit which comes with the 2 motors you need, but no controller.
Then you can choose your own controller, such as Crumble or PICAXE and provide your own power source
such as: http://uk.farnell.com/pro-power/bh242b/holder-battery-4xc-snap-term/dp/1183120. Or maybe try a sweet surprise!
16. gPiO board for the Raspberry Pi – very hot from the press! http://gpio.co.uk/. This is a very user-friendly and
powerful computer sense-and-control designed specifically to support programming in Python and Scratch
with the GPIO pins of a Raspberry Pi costing £74 inc P&P. It comes with a connector cable and plug which
fits over the pins of a Raspberry Pi and a micro-SD card with the ScratchGPIO software and examples already
installed. You can run the standard `Blinky’ test program to flash any on-board LED. But, as with Crumble,
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once you plug in an external power source, such as from a 6V battery box, then you can power external
outputs including the motors, buzzer and LED units
from the K’Nex packs above. So all you need to do now
is to choose your favourite inputs and outputs from
whatever kits you have acquired (such as a pair of the
K’Nex or LEGO WeDo or Crumble motors), get yourself
an external power supply for the Raspberry Pi and build
yourself a chassis in Meccano, LEGO, K’Nex or make one
from scratch to create a Raspberry Pi controlled
autonomous vehicle. To use the `Motor’ ports on the
side of the unit you will need to use the `Scratch
GPIO5+’ software supplied on the SD card. The
instructions are at: http://resources.gpio.co.uk/q-a/. Look at the
answer to the `How do I use the Output Circuits?’
question. A suitable power supply is:
http://www.maplin.co.uk/p/maplin-portable-power-bank-10000mah-n95lh. Can you do better than this: http://www.botmag.com/themars-exploration-rover-kit/?
There are plenty of sample programs to try at: http://resources.gpio.co.uk/ as well as videos such as:
https://www.youtube.com/watch?v=E4gT2u6CBnY&feature=youtu.be .
17. Raspberry Pi toppings aka `HATS’ – watch this SPACE! As we have seen there are many low cost devices
designed to plug into the GPIO pins to make gadgetting simpler. With the advent of the B+ version with 4
USB ports and more GPIO pins, the Raspberry Pi Foundation has come up with a specification of `Hardware
Attached on Top’ aka HAT boards: http://www.raspberrypi.org/introducing-raspberry-pi-hats/. The first of
these has been designed to support a new competition for schools (primary and secondary) to design
experiments for the British astronaut, Tim Peake, to take with him later this year when he goes on board the
International Space Station! The competition is called Astro Pi: http://www.astro-pi.org/.
18. LEGO revisited – graphical programming with WeDo In Section 4 of
Part 1 I mentioned the LEGO WeDo system which can be used together
with Scratch to control the output (motor) and respond to the inputs
(motion and tilt sensors). I also mentioned that you can also program it (at
a price) with LEGO’s `WeDo Software’ which is based on the internationally
used `LabVIEW’ system designed by National Instruments:
http://www.ni.com/labview/. I confess that I found the WeDo software quite hard
to understand at first – but my 11 year old grandson took to it like a duck
to water! It is very visual and offers no apparent help or instructions –
which avoids the need to have to produce different language versions!
Here is an example of a very simple program which just counts.
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Icons are dragged from the menu at the bottom of the screen and placed in a horizontal line from left to
right. The first icon in the main block of a Project is the yellow Start icon. The red second icon used is one to
display a message or number on the little display screen – in this case an `empty’ message to clear the
display. The red third icon adds a 0 to the display. The fourth yellow icon is a loop structure. With a number
box dragged below the end part you can make this a counted loop – equivalent to `Repeat 10’.
Without the number it will be a `Forever’
loop. The first icon inside the loop is a yellow
command to wait 1 second (I think the units
are 1/10 second). The next red icon adds 1 to
the number on the display. You run the
program by clicking on the green arrow on
the first icon. You can interrupt the program
by clicking on the red arrow on the right edge
of the screen. What would the same
program look like (a) in Scratch, (b) in a
flowchart or (c) in Python?
You can find out more in the `User Guide’:
https://c10645061.ssl.cf2.rackcdn.com/resources/wedo%20user%27s%20guide.pdf.
I am running the program with a LEGO WeDo USB block, motor and motion sensor attached – which is
shown in the top left-hand corner of the display above. So let’s see how we can interact with these devices.
First we’ll try controlling the motor. Output icons are in green.
We control the speed of the motor with the first green block,
and then switch it off with next. Then we have a forever loop
which waits 2 seconds, then turns the motor on for 2.5
seconds, then waits for 2 seconds, then reverses the motor
and runs it for 2.5 seconds before repeating the process.
Can you imagine how a motor-driven buggy would be moving?
Now we can exert (limited) control by using the motion, or tilt, sensor.
The first green block in the loop tells the motor to run not for a given time
but until the motion sensor detects something in its
path. Then it will stop, give a little chirp. Then wait
a second and if the path is now clear it will get
moving again until it encounters another object.
Of course we have quite a few constraints with this
system. Physically it is not autonomous and so we
can only move as far as the lead to the USB block
allows. Secondly we cannot fine-tune the motion
sensor as we can in Scratch. With this software it
just acts like a bump-switch returning the values
“not close” or “too close”.
But now we have met the notion of graphical programming we can see how LEGO have built on it to control
their more sophisticated Mindstorms devices.
19. LEGO Mindstorms NXT 2.0: The first model I bought was
called Mindstorms NXT 2.0 – as it was the `must have’ toy at that
time, 2009 – albeit with a price tag around £250. The name
`Mindstorms’ was the title of a seminal book by Seymour Papert,
the father of the LOGO programming language, published in 1980:
http://www.amazon.co.uk/Mindstorms-Children-Computers-PowerfulIdeas/dp/0465046746.
The hardware and software roots of the
Mindstorms Robotics Invention System kit go back to the
programmable `brick’ created at the MIT Media Lab. This brick
was programmed in Brick Logo. The original Mindstorms Robotics
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Invention System kit contained two motors, two touch sensors, and one light sensor. The first NXT version
had three servo motors and one light, sound, and distance as well as 1 touch sensor. The NXT 2.0 came with
3 motors, 2 touch sensors, a light sensor and distance sensor.
You can see an example of my own efforts with NXT 2.0 at:
https://www.youtube.com/watch?v=-NMzLA_Ib7k&feature=youtu.be
The NXT-G programming language uses a very flexible graphical interface with
boxes along the same lines as WeDo. We will build up the program used for the
simple `Mars crawler’ simulation in the video. When you start a new program a
new tab appears above a new worksheet containing just a single small icon
called the `starting point’. Everything connected to the starting point will be
loaded onto the NXT `block’ when you use the `Controller’ pad to `Download’. The
controller pad is at the bottom left of the worksheet. You build up a program by
dragging an icon from one of the tool menus at the left-hand side.
We will start by using the `Common’ blocks menu, and clicking on the `Wait’ (hour-glass)
icon. This opens a choice bar for the various sensors: time (clock), touch, light, sound, distance and colour.
Select the colour sensor and drag it next to the
starting point. Click on the icon and it opens a
dialog area at the bottom left of the screen. I
have selected the Control as a Sensor, and the
Sensor as a Color Sensor. I have specified that it will be attached to input port 4 of the brick. As we’ll be
waiting for the simulated Sun to rise over Mars we don’t need to check for any particular colour – just for
enough light. Use the slider to select the threshold value on a scale from 0 (dark) to 100 (full sunlight).
Check the `Light’ button rather than the red, green or blue ones. When we have enough light we’ll be
moving forward checking out what lies ahead!
But first we’ll give a wake-up call by adding a Sound
block. We can choose a built-in sound file or record our
own. I have selected the `Goodmorning’ file and set the
volume level at 75. Drag the Sound block onto the
program line. Now we need a `Repeat move until object
sensed’ block. Select the `Loop’ tool and click on the
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loop block to open up its dialog box. Select `Sensor’ as
the `Control’ and `Ultrasonic sensor’ as the `Sensor’.
Select input port 4, the units of measurement as
Centimeters and drag the slider (or type the number in)
to set the threshold distance as 52cms.
In order to put the filling into the sandwich we need to
use the `Move’ tools and the `Motor’ block. Open its
dialog box and click on the ports to which you will have
the motors attached and which you want to run – in my
case A, B and C. Select the Directions you want to apply – in my
case all going forward. Select the power level as 36 and the
duration as `Unlimited’. Add the block between the jaws of the
loop block.
Now we have the first phase complete. We won’t continue in
the same detail, but just look at the completed program. The
repeat loop drives all 3 motors forward until the distance sensor
picks up something within 52 cms. Then the motors are stopped,
another sampled sound is played and the blue light is flashed. After 5
seconds the motors are run in reverse for 3 seconds and finally the
light is switched off and a final sound is played.
I think you’ll agree that this is a pretty impressive environment for coding a quite complex set of instructions.
Now we’ve developed the software it’s time to build and
connect the hardware before putting it to the test!
The image shows the stripped down block with the three
motors attached to output ports A, B and C. The sensors shown
connected to output ports 1, 2, 3 and 4 are touch, sound, light
and distance. For the `Mars crawler’ we do not need to use
ports 1 or 2. As well as the 3 outputs and 2 inputs we also have
a USB cable connected to the computer.
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Now is the time to use `Save as…’ to give your program a name and to store your program on the computer
before using the Controller in the NXT-G software to Download the NXT file to the brick with the USB cable.
A downloadable version of the software is available from: http://service.lego.com/enus/helptopics/products/themes/mindstorms/mindstorms-nxt/nxt-software-download .
The LEGO Mindstorms NXT 2 kit made a significant step forward in user-friendly practical computing, but at
quite a high price. A quick trawl round e-Bay, Amazon etc. shows that this version is now out of stock and
that there are very few cheap bargains are to be had. So if you are starting from scratch and have the cash
then the next step, the EV3, is the one for you.
20. LEGO Mindstorms EV3: I bought the retail kit 31313: http://www.lego.com/en-us/mindstorms/products/31313mindstorms-ev3 which usually retails at £300, but can be picked up for c£250. Both the hardware and the
software have been redesigned. Here is the same program we just constructed for the NXT 2.0 in the new
EV3 Home Edition software. There are now 6 colour-coded block menus along the bottom instead of 3
along the left-side. The green menu shown provides the output bricks e.g. for motor control. The two
`repeat x until y’ loops have now been given names. The first loop has no filling, so it just stays waiting until
the value read by the light sensor is greater than or equal to 50.
Instead of opening a dialog box to enter choices e.g. for the
termination condition of the first loop, the parameters are
entered through drop down boxes. Here we set up the first
loop to be controlled by the `Color sensor’ by reading its
ambient light intensity and comparing it with a threshold
value of 50.
The `Good morning’
message for the
`Sound’ block was
recorded using the
`Sound Editor’ from
the `Tools’ menu.
The only difference
between the ways
the NXR 2.0 and the EV3 versions work is the way the light is flashed when the distance sensor detects the
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presence of something in its path. This time we have control over the coloured LEDs in the brick’s own
console. Once the Sound block has given the `a martian’ message, the first Brick status block starts the
green LEDs pulsing before the motors run in reverse for 5 seconds. The second Brick status block turns the
green LED off before the Sound block gives the `Good night’ message.
My tame technology tester, aka Alexander (age 12), took this a lot further forward in the new EV3 version
where he has very quickly discovered how to link the boxes in parallel to carry out parallel processing!
On the hardware front there are significant improvements including built-in Bluetooth communication, a
mini-SD memory card slot and a USB port to which a Wi-Fi dongle could be connected. I have set my unit up
on a static test-rig so I can easily test the various inputs and outputs. I am also using a special connecting
brick to allow me to use probes from the Vernier data-logging collection – the one here is a temperature
probe. If you have the Educational version of the EV3 software there is also extensive support for using the
kit as a sensing device for data-capture. I haven’t done it yet, but we should be able to put an Ev3 brick in
the fridge with a light and temperature probe and check what happens when you shut the fridge door! Does
the light go off? Does the temperature fall? What happens when you open the door?...
For both the NXT 2.0 and EV3 it is very helpful to have an ideas book to help you explore new ideas. I have
`The Unofficial LEGO Mindstorms NXT Inventor’s Guide’ by David J. Perdue: http://www.amazon.co.uk/Unofficial-LEGOMINDSTORMS-Inventors-Guide/dp/1593272154 and `The LEGO Mindstorms EV3 Idea Book‘ by Yoshohito Isogawa:
http://www.amazon.co.uk/dp/1593276001/ref=pe_385721_51767431_TE_dp_1 .
21. LEGO Mindstorms, Scratch and Bluetooth In the course of this mission to learn more about the state of
the art in physical computer I have made
contact with the designers of systems like
Crumble and PICAXE Microbot. In section 10
of Part 2 we met the clever S2P system from
Revolution Education which hooks up PICAXE
projects to Scratch 2. So I was delighted to
discover the support Revolution is giving to
schools around Bath using hardware such as
LEGO Mindstorms. S2Bot is the free tool for
connecting other kit, equivalent to S2P
(Scratch to PICAXE):
http://www.picaxe.com/Teaching/Other-Software/ScratchHelper-Apps/.
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First you need to ensure the EV3 is not connected to any other software, as its Bluetooth option turned on,
and is set to be recognised by other devices. Then you need to pair your computer’s Bluetooth (internal or
external) with the EV3 by sending and receiving the `1234’ code. When communication is established, use
Device Manager, or equivalent, to find which COM Port your EV3 connection is made through. Mine is COM
41. Once you have established Bluetooth connection with NXT 2.0 or EV3 you can run S2Bot and open the
connection ready to use with Scratch. Select EV3 as the Target and COM41, or whatever your computer
uses, as the Bluetooth Port. Click on the Connect button and with luck the EV3 will be connected. The panel
show which sensors are connected to the input ports 1, 2, 3 and 4 on the brick. The Test pop-up allows you
test that commands can be sent to the brick as well. Now you can open Scratch2 and the open the
corresponding template such as `EV3 template.sb2’ and look under `More Blocks’ – lo and behold there are
now a complete set of tools to read data from the sensors attached to any of the 4 input ports, to send
output to 3 motor ports and to the brick’s sound and light systems.
So here is the Scratch equivalent of the `Mars Rover’ program for EV3.
I have also taken the opportunity to show off the use of a couple of procedure (sub-programs) to make the
Scratch program fit in a single edit window without needing to scroll! Also note the way we have built a
timed loop using the `timer’ blocks from the `Sensing’ menu. I used Scratch’s Sound Editor to record and
save the 3 sound files for the messages – which are played back on the computer. It is also possible to play
`rsf’ sound files recorded in the LEGO EV3 software and uploaded to the brick – but I haven’t made that work
yet! Can you adapt the `Distance Time Graph’ we wrote in Scratch for the LEGO WeDo distance sensor to use
any of the EV3’s sensors for data-logging? If you have of any of the Vernier sensors you can plug them into
the EV3 or NXT using an adaptor block costing £45: http://www.inds.co.uk/engineering/lego_nxt.htm.
Adrian Oldknow [email protected] 30th March 2015
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