TARDIS build is coming
along, but am finding the learning curve for this coding stuff is actually
quite hard. blog.mindrocketnow.com
Our summer holidays project to make a cardboard Tardis
paused whilst other summer activities took precedence. Suddenly, we’ve got two
weeks of holiday to go, and we’ve not progressed much further. Quick – start
building!
The bulk of the construction was already done, just the
decorating and the telephone to install. We abandoned the collage idea, and
went with the quicker writing out by hand. The box is going to house the emergency
telephone, and now needs to be attached to the TARDIS with a duct tape hinge.
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The writing might be a little wonky
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The next part of the build is going to be a little tricky.
We only have a small blue LED, so to make it visible we can either put behind a
lens in a lantern. Or we can cover the lantern with blue acetate and use a
bunch of white LEDs. I think we should try the former, because we have the
parts already, and it might actually be brighter than the latter.
Having seen the limited appetite of the DDs to learn coding
by googling for answers, I decided to write the next version of the TARDIS
program myself, to present to them afterwards. However, I underestimated my own
recollection of coding from university days. I now realise that not only do I
not know the python programming language, but I’ve also forgotten how to read
and understand API documentation.
My late night surfing for code examples for newbies showed
me that the barrier to learning is quite significant; there’s an expectation
that you know the basics before questions are answered. I know the DDs won’t
have the patience to work it out with me, so I’m going to have to go through it
so that I can explain back to them.
Case in point was playing the sound file of the TARDIS de/rematerialising.
I’d already installed VLC, which has a nice Xwindows interface. The DDs were
able to play the sound just by right clicking on the file. But how to invoke
VLC in a python script? Even though there are some well-documented python
bindings for VLC, I couldn’t understand them. So I was unsurprised when my
simple code didn’t work. (To understand the following code snippet: pin 23 is
connected to the switch, and pin 24 is connected to the blue LED. The idea is,
when you push the switch, the LED flashes in time with the sound.)
import RPi as
GPIO
GPIO.setmode(GPIO.BCM)
import time, vlc
GPIO.setup(23,
GPIO.IN)
GPIO.setup(24,
GPIO.OUT)
player =
vlc.MediaPlayer(‘Tardis.mp3’)
while True:
if
GPIO.input(23):
GPIO.output(24,
True)
player.play()
time.sleep(1)
GPIO.output(24,
False)
time.sleep(1)
else:
GPIO.output(24,
False)
time.sleep(0.1)
I couldn’t get the sound to repeat. Whilst I kept my finger
on the button, the LEDs flashed, but the sound played only once. I also
couldn’t figure out why I needed that first time.sleep(1)
command (in the if section); surely the LED would
only stay lit for as long as the file was being played, thereby being
synchronous?
Searching for why it wasn’t working just sent me to the VLC
python bindings documentation, which seems to me both comprehensive and unintelligible. I
think I need a better understanding of how API documentation is written in
general before I can understand the VLC one. So I gave up, and tried to find
another way to achieve the same end.
Whilst searching for how to make a doorbell using a RPi
(press button – make sound), I came across this great
article from Adafruit (incidentally, a source of a number of interesting
project ideas). The answer, it seemed, was to use a different player, mpg321,
and to invoke from the operating system command line, not via a python binding.
The code then became:
import RPi as
GPIO
GPIO.setmode(GPIO.BCM)
import time, os
GPIO.setup(23,
GPIO.IN)
GPIO.setup(24,
GPIO.OUT)
while True:
if
GPIO.input(23):
GPIO.output(24,
True)
os.system(‘mpg321
Tardis.mp3’)
GPIO.output(24,
False)
time.sleep(1)
else:
GPIO.output(24,
False)
time.sleep(0.1)
And it worked! So DDs and I amended their code from last
time with my newly-worked out code, and we made the LED flash in time with the
dematerialisation sound.
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Can you see the LED (next to DD2’s hand) lit?
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TARDIS Project Plan - Update
a) Planning
* Draw picture of what
we want to build (done)
* Draw cause-effect
diagram of how we want the program to work (done)
* Create a shopping
list for the stuff (done)
b) The TARDIS box
* Paint the box blue
(done)
* Install in doorway
(done)
* Paint the “Police
Public Call Box” sign (done)
* Decorate and attach box for telephone handset (half done)
* Find a light lantern, and attach lens, for the blue LED
* Make mount for TARDIS ignition key switch
c) Programming the Raspberry Pi
* Learn how to make an
LED flash (done)
* Learn how to play a
sound file (done)
* Learn how to play a sound file through an external speaker
* Write a program
that flashes an LED and makes a whooshing sound, in sync (done)
d) Connecting the Pi to the TARDIS
* Buy the components
and check that they connect together (a bit done)
* Build any bespoke connectors
* Prototype the light
and sound rig on breadboard (done)
* Build final rig, and test that it all works
More things learnt
* Painting and decorating is more interesting to electronics
and coding, at least to my DDs. Therefore do more painting, and make the coding
less demanding.
* Before attempting to teach coding, work through the code
yourself first. Things that you assume will work first time, won’t.
* Sometimes knowledge is hard-fought yet won. Other times,
it remains elusive. Teaching is to make it worth the challenge.
More in this series: part
7.
