2-1 Simple Circuits

Overview

Goals

• Students will be able to understand and construct simple circuits.
• Students will be able to identify necessary components of a circuit (power, conductors, polarity, etc.)
• Students will be able to describe the transfer of energy in a circuit.
• Students will be able to explain how we use programming to manipulate the transfer of energy in a circuit.

Content Standards

Prep

Teachers should complete the following preparation for the lesson:

• Make sure computers have internet and work.
• Ensure that MakeCode is not blocked; talk to IT if necessary.
• Prepare supplies as a kit per student pair (copper tape, 1 LED, 1 CPX, 2 alligator clips, 1 coin cell battery, 1 coin cell battery holder)
• Make copies of Simple Circuit Diagram on card stock and cut out the templates (1/pair).
• Have copies of Intro to Programming handout (1/pair).
• Have link to Simple Circuit Start Code ready to give to student pairs.
• Place students into pairs.
• Write warm up question on the board.

Lesson Guide

Introduction (10 minutes)

Place students into pairs. For each pair, pass out a supply kit. Model what a coin cell battery and LED look like, and ask students to take both out. Tell students that the LED is like a light bulb and the coin cell battery is a battery. Challenge students to turn the LED on by connecting its legs to the coin cell battery.

Wait for all pairs to turn the LED on.

Ask students:

Does it matters which LED leg is touching which side of the coin cell battery?

The positive leg of the LED (the longer one) needs to be touching the positive side of the battery, and the negative side of the LED needs to be touching the negative side of the battery.

Draw the following diagram on the board:

Tell students that the image represents a circuit. Electric energy, called current travels from the positive side of the power source to the positive side of the LED. The current then travels through the LED and its energy powers the LED on. The current then flows out the negative side of the LED to the negative side of the power source. The circuit forms a closed loop. Current flows from the positive side of the power source and comes back to the negative side of the power source.

Add the following arrows to the diagram:

Current only flows through material that is conductive. The legs of the LED and the outside of the battery is conductive, meaning that the current can travel through it. Show students the alligator clips they can find in their kit; explain that the alligator clips are also conductive and that current can travel through those as well.

By the end of this section, students should understand that a circuit is a closed loop of conductive material connected to a power source that allows current, or electric energy, to flow from the positive side of the power source through the loop back to the negative side of the power source.

Simple Circuit Diagram and Instruction (20 minutes)

Teacher passes out Simple Circuit Diagram. Explain that the card stock is an insulator. Write insulator on the board if not already there. Explain that an insulator blocks energy flow. Current cannot flow through an insulator. In this case, the current will not leave the copper tape and bleed into the card stock.

Teacher invites students to take out the LED. Explain that the goal is to create a circuit that turns on the LED. Write Light Emitting Diode on the board.

Invite students to place the LED on the diagram. Direct them to the positive and negative sign on either side of the LED symbol. Write the word polarity on the board. Explain that power sources have two poles: positive and negative. Current flows from the positive side to the negative side. The positive node of the LED must be securely connected to the positive side of the power source, and the negative side of the LED must be connected to the negative side of the power source. We use conductors (like copper tape) to connect components like LEDs to a power source. A common error made when making circuits is reversing the polarity of components. For example, flipping the LED so that the + and – sides are reversed. When we draw circuit diagrams in this class, we will distinguish positive as a red + and negative as a blue -. We always label the polarity of each of our components.

Teacher invites students to take out copper tape. Write conductor on the board if not already there. Explain that conductors allow for the flow of energy. Conductors do not have polarity; they just allow the current to flow so we can use the same conductor on both sides of the circuit. We need to connect the conductor to a power source or there will be no current.

Model best practices of laying down the copper tape: use one large piece per side; when making a corner, fold the opposite direction you want to go, and fold back down in the direction you want to go, as shown below:

Invite students to individually construct the simple circuit on the diagram template by laying the copper tape on each side.

The two sides of the copper tape should not touch. There will be a gap between them where the LED goes. Touching positive to negative is called a short circuit, and the circuit will not function. Each line of a circuit should only touch the component (here the LED) and the power source.

Mention that we have not yet included a power source. Invite students to take out the coin cell battery holder, and put the battery inside the holder, making sure to connect the positive side of the battery in the correct direction.

Invite pairs to remove two alligator clips from the kit. Connect one alligator clip from the positive side of the copper to the positive side of the battery holder and the second from negative side of the copper tape to the negative side of the battery holder. The LED should turn on.

Think-Pair-Share

Use the vocabulary on the board to describe how energy flows through a circuit.

Turn the Lights On: Intro to Programming (20 minutes)

Tell students that we will replace the power source. Currently, we are using the battery, which sends constant current through the circuit to turn on the LED. But now we will find out what the Circuit Playground does.

Teacher posts link to Simple Circuit Starter Code in MakeCode and demonstrates how to remix the code for editing.

At the starter code, click “Edit” at the top of the page.

Invite students to take out the CPX. Write the word microcontroller on the board and explain that a microcontroller is a computer that does a single task.

We download code into the microcontroller, and it can only do that code, repeating it forever. Point out that there are microcontrollers everywhere: streetlights, elevators, escalators, automatically opening doors. Any time you have a device that has a single purpose, microcontrollers are there.

Model how to connect an alligator clip from negative line to ground and positive line to the A7 pin (as shown).

xplain that ground is the negative pole, and the numbered pins are positive poles. Inform students that Vout will not be used in this unit, and 3.3V is a pin that is always on. All the other numbered pins must be instructed to turn on and off to allow the energy to flow. When A7 is told to turn on, or set to HIGH, energy will flow from the A7 pin through the conductor, across the LED, and back to ground. When A7 is turned off, or set to LOW, we block energy from flowing.

Tell students that we do not program ground, which is negative. We just need ground to allow the current to come back to the power source after passing through the LED(s).

The point of this section of the lesson is to get students to understand that current flows out of the positive pole of the power source. We can control the positive pole to either allow the current to flow or block the current. We do this using code.

Invite students to connect the CPX to their circuit and download the code.

The LED should turn on. If it does not, help students fix the circuit by checking the connections.

In pairs, students read through code and write down three questions they have about the blocks they see. Teacher fields questions. During question fielding, if the question does not come up, ask which pin they think “digital write pin A7 to HIGH” is communicating with and what it does.

The forever block repeats the code inside of it forever. The digital write pin A7 to HIGH block sends current to pin A7, which then flows along the circuit that we created using the copper tape.

Tell students that they will work together to make the LED blink on and off every second. Explain that we must be very specific when we give instructions to a computer.

Pass out Intro to Programming Handout. Invite students (in pairs) to write down on the handout what it means for an LED to turn on and off every second (part 1). Say that we always storyboard our code before we program. Programming is the process of translating human intention so that a computer can act on it. When ready, invite students to share their storyboards out loud. Look for “turn led on, pause 1 second, turn led off, pause 1 second, repeat forever.”

Direct students to Part 2 on the Exploring Circuits handout. Invite students to use the blocks in MakeCode to translate their storyboard. When done, students should download their code to the CPX. The LEDs should blink. If errors occur, invite students to read through their code and see how each line represents their written storyboard, looking for some inconsistency.

Homework

Direct students to Part 3 on the handout. Invite students to explain how the code and pins on the CPX control the flow of current through the circuit to turn the LED on and off.

Vocabulary

The following are terms used in this lesson.