Lesson 8

Lesson Overview

Students are able to understand the use of single choice control structure and variables in programming.
Students are able to produce a tortoise project that hides its head when the micro:bit is shaken at least 5 times.

6.3.1 State selection and repetitive control structures in programming.6.3.2 Describe selection and repetitive control structures in an algorithm.6.3.5 Evaluate the generated pseudocode or flow chart to detect errors.6.4.3 Produce a project flow chart that emits light, sound, and movement.

Did you know that tortoises use visual cues to remember their food sources?

Like the tortoise, a variable waits for a number or text signal to run a specific program.

Hmm... how to trigger a program without using an event block?

Single-Selection Control Structure

A single-selection control structure is a system that has only one branch of a specified condition.

Sample of single-selection control structure.

Let’s learn how to program the micro:bit using a single-selection control structure.

Video 8: Tortoise (Part 2)

Watch and follow this video to get to know how to build a tortoise project that hides its head when the micro:bit is shaken.

Materials needed to follow this video:

micro: bit + USB wire + connector wire +3 alligator clips + 3V servo motor + power supply
Computer
Visit makecode.microbit.org
Plastic bottle + colored paper + cardboard

TIPS Challenge in the Video

Transcript

Hello world! Welcome back to the microbit series. I am Alina and
today we will complete our tortoise project.
In the previous video, we had used variable
to count the time microbit is shaken. This time,
we will add a servo motor to pop out
the tortoise's head when the microbit is shaken.
Prepare all these project materials like the previous video,
but this time we add connecting wires,
micro servo motor 3V, 3 wire clips,
power supply or battery. Cut out the plastic water bottle
to make the tortoise's shell. Make sure to make the holes for
microbit to be displayed and the tortoise's head
to pop out. Cut out the tortoise's head.
Insert the blade to the servo motor.
Screw it tightly
and stick that blade to
the tortoise's head just now.
Connect the wires to the servo motor. White wire to
the orange wire, red wire to the red wire and the brown wire
to the black wire.
Clip the white colour wire to pin 0,
black colour wire to GND
and red wire to 3V.
For the video this time, we try to program the microbit to
pop out the tortoise's head when the microbit
is shaken for at least 5 times.
We need to use
single selection control structure or single choice conditional.
We can use logic blocks to execute
single selection control structure.
We use the block "If-then".
If the condition is fulfilled, the blocks that are contained in the selection block
will be executed.
The condition can be set using the comparison blocks.
If the comparison is correct, this block will execute
the programming blocks in it. For this project, we will set the count
bigger or equal to 5.
We put in the servo motor programming
into the selection block just now.
Set servo P0 angle
to 90 degree.
Add the pause block
for 500
milliseconds.
Set servo P0 angle to
0 degree.
Add the pause block for 500 milliseconds.
Repeat these blocks to return the servo motor
to its original position.
Connect microbit to the computer with
a USB cable.
Press download on the software and save the programming file into the microbit.
Remove the USB cable from microbit.
Connect the power supply or battery to the microbit.
Switch on the power supply and observe what will happen when
the microbit is shaken.
First shake,
second,
fourth,
and fifth.
The tortoise's head will only pop out if the microbit is shaken
for at least 5 times.
Tidy up your project and try to arrange the wire and
microbit board so that they are not seen from the front.
Your tortoise project is done!
As a challenge, try to pop out the tortoise's head if it is shaken
for 5 times and withdraw back its head if
the tortoise
is shaken 7 times. Program your microbit to reset
the count when a button is pressed. Happy trying!

After watching this video, it’s your turn to try the assignments and challenges! They are:

Show the tortoise's head when the micro: bit is shaken at least 5 times.
Hide the tortoise head if shaken for 5 times and show the head if the turtle is shaken 7 times. Program micro:bit to reset the count when the button is pressed.

👉CLICK HERE👈 to try it on makecode.

Practice in the Video

Ways to build code.

End product.

Read the lesson notes below to deepen your understanding.

How to program Single-Selection Control Structure

A single selection control block in the “Logic” block drawer will be used. If the criteria are not met, no program will be executed.

Criteria can be set using comparison blocks.

Think about the last example:

To make the program work, the micro:bit has to remember the count and decide to hide the tortoise's head if it needs to. Event-based blocks can’t do everything. Single-selection control blocks help with this!