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The following information is a single lesson in a larger project. Find more great projects here.

Lesson Overview:

Step 1: Introduction

In this lesson we use the blinker module which creates an alternating output that blinks LEDs and beeps buzzers.

The blinker module uses a chip called a 555 timer. This module turns its output on and off at a constant rate. This type of output is called a square wave. Its maximum voltage is the same as your power source (for example, 9 Volts) and its minimum voltage is 0 Volts (ground).

Like a photo sensor, the blinker is an “active” module that needs power from the battery.

1. Press the "next" button below to continue.

Step 2: Making a Blinking Light

Notice that a battery and blinker module are already in the Workplane. The (+) terminal of the battery is aligned with the VCC terminal of the Blinker, and the (-) terminal of the battery is aligned with the Ground terminal of the Blinker.

In this step, we’ll wire up the circuit and add two LEDs to use as output modules.

1. Open the Components + tab and bring two LEDs into the Workplane.
2. Position the LEDs to the right of the Blinker module and place one slightly above the other slightly below the Blinker.
3. Use the Conductive Pen to connect the (+) terminal of the battery to the VCC terminal of the Blinker.
4. Connect the (-) terminal of the battery to the Ground terminal of the Blinker.
5. Connect the (+) terminal of the battery to the VCC terminal of the Blinker.
6. Looking at the top LED, connect one terminal to the output of the Blinker and the other terminal to the VCC foot.
7. Now looking at the bottom LED, connect one terminal to the output the Blinker and other terminal to the Ground foot.
8. Press the "next" button below to continue.

Step 3: Simulating the Circuit

When you simulate the circuit, you will see the lights blink on and off at a constant rate.

There is a green indicator light on the module. This light lets you know the module is powered and what rate your circuit will blink at.

There is also a potentiometer on this module. You can change the rate of blinking by turning the dial. Give it a turn while the simulation is running!

1. Start the simulation by pressing the “Start Simulation” button.
2. While the simulation is running, turn the dial on the Blinker module by clicking on it and dragging your cursor around the perimeter. What happens to the blinking rate?
3. Try to adjust the Blinking rate so the light stays on for one second and is off for one second.
4. Press the "next" button below to continue.

Step 4: Understanding Your Circuit (part 1)

The Blinker module produces a square wave, which is a type of waveform. A waveform is simply an electrical signal that changes its value over time. In this case, the voltage at the output changes between a maximum value (9 V) and a minimum value (0 V) at a constant rate.

If you look at a plot of the voltage over a period of time, it would look like a series of rectangles stacked together. An example is shown below. The white drawings on the Blinker module itself also represents a square wave.

As you turn the wheel on the Blinker module, the “frequency” of blinking changes. This is the number of up and down cycles that occurs per second, and expressed in units of “Hertz.”

If your light is on for one second and off for one second, that is one cycle every two seconds -- or 0.5 Hertz.

1. Press the "next" button below to continue.

Step 5: Understanding Your Circuit (part 2)

There is something else that happens while the circuit is being simulated: one light blinks on while the other light blinks off. What is happening?

The function of the module is a lot like the photo sensor. Let’s focus on what happens when the square wave output is at it’s highest point, 9 Volts.

Output HIGH:

Since current runs from points of high voltage to points of low voltage, it will pass through the output of the Blinker, through the LED, to the Ground foot (0 V). The bottom LED lights up. The top LED does not light up because there is no voltage difference across it.

The picture shows what happens when the output is high -- there is a voltage drop across the bottom LED, and it turns on.

1. Press the "next" button below to continue.

Step 6: Understanding Your Circuit (part 3)

Next, let’s see what happens when the output square wave is at its lowest point, 0 Volts.

Output LOW:

Again, current will flow from a point of high voltage to a point of low voltage. In this case, current is flowing from the VCC foot of the Blinker, through the top LED, to the output terminal. The top LED lights up. The bottom LED does not light up because there is no voltage difference across it.

The picture shows what happens when the output is low -- there is a voltage drop across the top LED, and it turns on.

1. Press the "next" button below to continue.

Step 7: Printing Out Your Circuit

After setting things up, try out a different output module, like the buzzer. You’ll use this circuit in the final project.

1. Print out your circuit template and try it with your Circuit Scribe kit.
2. Press the "next" button below to continue.

Congratulations on completing a circuit that uses a square wave signal! Can you think of a device that uses a blinking light? (see the hint for an example)

You’re almost ready for the final project: a touch sensor alarm.

Next Lesson:Final Project - Pressure Activated Alarm

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