
SILO 4.3 (DRAFT) Year 4, Term 3: Sensors Focus: Analog to digital conversions Scope and sequence: Analog to digital conversions
Learning intention: Students use micro controllers to monitor and log data from electronic sensors.
NSW Syllabus	Australian Curriculum (version 9.0)
“A student explains how digital systems represent data, connect together to form networks and transmit data.” (ST3-11DI-T)	"Students learn to implement simple algorithms as visual programs involving control structures and input." (AC9TDI4P04)

Introduction to the topic

Electric sensors can sense changes in the physical world such as temperature, moisture and acceleration. When used in conjunction with devices such as micro controllers, sensors can be used in various ways to interact with our surroundings.

Symbols game

The <, > and = symbols were covered in SILO 1.2 'Symbols'. The following game build on this knowledge in the context of coding and the concept of 'IF THEN'. Paper cards could be made but cardboard works better. The image below shows number cards and symbol cards. The numbers are between 1 and 100 but the symbols cards have = on one side and < on the other. Depending on the orientation of the < card it could be < or >. The game is played as follows:

Each student is given a number card and a symbol card.
Everyone stands in a circle facing each other holding the cards in front of their chest or stomach so everyone can see them clearly.
The number card must go in the right hand and the symbol card in the left hand.
Depending on the number, each student must arrange their symbol card so that the sequence is correct.
The teacher starts by stating their number followed by their symbol. For example, "32 greater than".
The pattern continues moving clockwise around the circle. For example, "12 less than", "60 less than", "91 greater than", "15 less than" and so on.
Any errors in the symbol orientation should be fixed before moving on to the next person.
When everyone in the circle has had their turn the students are given 5 seconds to shuffle into a new position in the circle but they must keep the same two cards.
A new game then commences.

Teaching notes: The photo above shows the cards but without any students. Some children might have trouble reading upside down so remind them that their number is the same in each round of the game so they can easily memorise that. The < symbol will look like a > when viewed upside down (and vice versa) so remind them that it is about how the other students see the cards.

Types of sensors

This video by Martin Levins titled Sensors 1 (5:10) provides an excellent introduction to sensors.

This video by Martin Levins titled Sensors 2 (7:46) provides an overview of some commons sensors and how they work.

This video by Martin Levins titled Sensors 3 (4:47) shows how sensors can be used with micro controllers such as the micro:bit.

Potentiometers

Potentiometers (pots) are variable resistors. Because the resistance can be varied by turning the shaft, usually accompanied with a knob, they are often used for applications such as volume controls.

(Image source: https://en.wikipedia.org/wiki/Potentiometer#/media/File:Electronic-Component-Potentiometer.jpg)

By using the following code, the simulator will display the resistance on a scale of 0 to 1023 if you drag your cursor along Pin 0 on the bottom left-hand side.

Connect a pot to your micro:bit as follows (Image source for diagram https://www.teachwithict.com/potentiometer.html). Note: The photo shows a pot which is designed to be mounted onto a Printed Circuit Board (PCB) so there are three pins rather than rounded lugs but you can't see this through the black tape. The alligator clips had less metal to attach to so the wires have been soldered on to make it easier to use in a classroom. The wires also happened to be different colours to those in the diagram.

This volume control activity is extended in SILO 6.3 'Robotics' where the number in the readout is manipulated in various ways to behave like a more traditional volume control.

Making a simple synthesizer

Using the same cables to connect the pot to your micro:bit you can make a simple synthesizer. As you rotate the knob you will produce a continuously variable frequency using the following code:

The main concept in this unit is understanding the difference between analog and digital. The following video (7:12) titled Digital vs analog. What's the difference? Why does it matter? explains this well.

The following screenshot from the same video helps illustrate the difference between digital and analog using variations in colour.

Sensing moisture

This video (6:43) shows how the micro:bit can be programmed to measure moisture in soil to create a water monitoring system.

You could choose to have the reading displayed continuously or when triggered by pressing a button. The example below displays the moisture level when Button A is pressed. The connections are to Pins 1 and 3V.