Operation Manual

A beginner’s guide to Scratch
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Now, we need to use the red patch on the car’s bumper as a red sensor. The
program will then be able to detect when the line turns left and tell the car to turn
to the left too.
Here’s the code you need to finish your LFV program:
As you can see, the program is run with a green flag event. After that:
n A “go to” block is used to position the car on the line.
n We the have used a “forever” loop to keep the car running.
n The car moves 0.5 steps (for each cycle of the loop).
n An “if” block is then used to check if the green spot on the car has touched the
black line. If it has, the car will turn to the right by 1 degree.
n Another “if” block is then used to check if the red spot on the car has touched
the black line. If it has, the car will turn to the left by 1 degree.
For an example of a completed version of this project, open
RPiScratch/Projects/lfv.
The level crossing
RESOURCES: The sprites “lights” and “barrier”, the background “level_crossing”
and the sound “level_crossing_a”.
Computer control systems can save lives. At a level crossing we have to make
sure that cars and trains never meet. This is done with a sensor on the track that
detects the passing train.
A computer then responds to this event by stopping the traffic approaching the
level crossing and closing the barrier. This control program can be written in
Scratch. But before we start, we need to import the necessary sprites and
background.
First, import the background “level_crossing”. As you can see from the picture on
the next page, the background shows the road leading up to the crossing, the
traffic-light box and the barrier support.
Tip...
Run the program
in full-screen
mode – it is more
impressive. Click
on the right-hand
button at the
top-right of the
Scratch window,
just above the
green flag and
the red circle.
Tip...
If your car stops
at an odd angle,
and you can’t
straighten it out,
you can import
the “yellow_car”
sprite again, drag
and drop your
finished script
onto the new
sprite and then
delete the
old one.