Introduction: Final Project - Pressure Activated Alarm

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

Return to Previous Lesson: Blink, Buzz! Blink, Buzz!

Lesson Overview:

Now we'll build our own basic alarm!

Step 1: Introduction

The circuits in most devices aren't really visible because they are covered by some kind of case. Hopefully this course has revealed some of the magic behind electronic devices in your daily life!

The final project is a pressure sensitive alarm. When a heavy object is placed on top of your device, a light flashes and a buzzer beeps.

In our example (below), a mini breadboard is making the alarm go off!

In this project uses the Blinker module, an LED and Buzzer, and finger electrode for the pressure sensor.

(Note: you can review Lesson 1 before moving to the next step)

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

Step 2: Materials

All of the modules that you need are already in the Workplane:

Battery

Blinker

LED

Buzzer

Finger Electrode (partially finished)

Switch (for the circuit simulation)

You will also need:

The Circuit Scribe Maker Kit

Paper Sheet of construction paper

Scissors A heavy object like a ceramic mug

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

Step 3: Building the Circuit

In the circuit design process, you can keep the modules where they are in the Workplane.

You will need to make the correct connections using the Conductive Pen and complete the finger electrode.

You can start by trying to build the circuit based on the description. If you get stuck, move onto the next step for design tips!

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

Step 4: Design Tips (part 1)

We suggest wiring up the blinker module first. This is an active component that needs power from the battery!

  1. Select the Conductive Pen.
  2. Connect the (+) terminal of the battery to the VCC terminal of the Blinker.
  3. Connect the (-) terminal of the battery to the Ground terminal of the Blinker.
  4. At this point, try simulating the circuit to make sure the Blinker is blinking! The green light on the module will flash.
  5. Stop the simulation and press "next" to continue.
  6. Press the "next" button below to continue.

Step 5: Design Tips (part 2)

The LED and buzzer go off at the same time. A good way to do this is to connect them in parallel.

  1. Select the Conductive Pen and draw a connection between the top terminals of the LED and Buzzer.
  2. Connect the bottom terminal of the LED to the bottom terminal of the buzzer.
  3. Press the "next" button below to continue.

Step 6: Design Tips (part 3)

The buzzer and LED go off when you complete the circuit by pressing a conductive material on the finger electrode.

You will want to connect the Blinker in series with the LED, finger electrodes, and battery.

  1. Select the Conductive Pen.
  2. Draw a connection between the output of the Blinker and the top terminal of the LED.
  3. Draw another connection between the bottom terminal of the buzzer and the right side of the finger electrode.
  4. Draw a connection between the left side of the finger electrode and the negative (-) terminal of the battery.
  5. Press the "next" button below to continue.

Step 7: Design Tips (part 4)

Finally, you will need to complete the finger electrode.

We have drawn 4 fingers in for you, but there is a big blank spot in this area.

Use the conductive pen to fill in this area. You don't have to use straight lines -- you can make them diagonal or curved.

Just make sure that you have two separate electrodes!

  1. Select the Conductive Pen.
  2. To draw a line that is not connected to a component, start by clicking on one of the lines that is already in the Workplane.
  3. Draw your line or curve as usual.
  4. Double-click your cursor when you get to the end of the line.
  5. Press the "next" button below to continue

Step 8: Simulating the Circuit (part 1)

Take a moment to make sure your connections match the picture below. Next, we want to make sure that the fingers in the finger electrode are not touching!

Try simulating the circuit -- if the LED does not blink, then your electrodes are separated.

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

Step 9: Simulating the Circuit (part 2)

Finally, we want to see if activating the pressure sensor will make the LED blink and the buzzer beep.

We don't have a simulation for a conductive material - but we do have a switch!

Place a switch component across the finger electrode so it is touching both sides (see picture). Then simulate the circuit and turn the switch on.

  1. Open the Modules + tab and bring a switch into the Workplane.
  2. Place the switch on the finger electrodes so it spans both sides (see picture).
  3. Simulate the circuit and flip the switch!
  4. Before you move on, stop the simulation and delete the switch. Make sure you delete the round pads too!
  5. Press the "next" button below to continue.

Step 10: Building the Project (part 1)

Start by printing out your circuit template and drawing the conductive lines with the Circuit Scribe pen.

  1. Download and print the PDF template.
  2. Draw over the template with conductive ink, and place your components. You can try activating the sensor by putting a conductive object down, like a coin.
  3. Press the "next" button below to continue.

Step 11: Building the Project (part 2)

You're almost there! Now you just need to design the pressure sensor pad.

1) Start with a piece of construction paper and cut it out into any shape! Just make sure it completely covers the finger electrode.

2) Flip it over and draw a 6 cm square on the back. Then fill it in with a conductive ink pattern. It doesn't need to be completely filled! We suggest using a diagonal grid (see picture).

3) Flip it over and place it on the finger electrodes.

4) Decorate the front with some text, like "Keep off!"

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

Step 12: What Will Activate the Sensor?

Congratulations on completing a pressure sensitive alarm system!

Try placing different objects on the construction paper. How heavy does it need to be to activate the alarm? How could you make it more sensitive?

Check out other great projects here.

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