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Lesson Plan #: AELP-PHS0212
Submitted by: Eric Price
Email: eprice@nrtco.net
School/University/Affiliation: Fellowes High School
Date: August 24, 2003

Grade Level: 5, 6, 7, 8, 9, 10, 11, 12


  • Science/Physics
  • Vocational Education/Trade and Industrial

Duration: Two 60-minute sessions

Description: In this activity, students will create a functional alarm circuit.

Goals: National Science Education Standards (NSES) :
Physical Science Content Standard E: As a result of activities in grades 5-8, all students should develop

  • Abilities of technological design
  • Understandings about science and technology


  • Students will be introduced to basic electronic components, specifically the SCR latching transistor.
  • Students will learn about electronic symbols.
  • Students will be able to construct a functional alarm circuit to protect a specific item.
  • Materials:

    Procedure: Step 1 : Make two copies of the Block Diagram: one to place on a styrofoam base, the other to observe while you construct the circuit.

    Step 2 : Observe the Battery Assembly Sheet drawings and cut out, using a utility knife, styrofoam so as to be able to place the battery. Create the two battery blocks from your styrofoam sheet.

    Step 3 : Place the cut-out Block Diagram onto a styrofoam base of the same size. Look for the Easye markers on the Block Diagram and place the Easye connectors pins on top of these four corner markers; then push straight down through the paper into the styrofoam base. Now insert the anchors (yellow) in same fashion.

    Step 4 : Place the terminal screws on the Block Diagram, using a screwdriver. Insert the terminal screws about halfway into the styrofoam base for now. Later you will wrap wire around each terminal and screw it completely into the styrofoam base.

    Step 5 : Insert all components except the buzzer; it will be inserted after the wires. Make sure you have the (Q) SCR and (L1) LED inserted correctly. Insert resistors (R1, R2, R3); if the leads are long, cut length and bend 90 degrees. Make sure you observe each resistor for the correct color code. See parts information on the Block Diagram for numerical values in ohms.

    Step 6 : Measure the hookup wire required from each point in the circuit; cut each to length and strip both ends. Bend wires to follow circuit layout and insert each wire into the Easye connector or anchors. Make sure you leave bare wire at each connection point. Wrap the wire tightly around each terminal screw and then completely screw terminal into the styrofoam base. Your sensor switch (clothespin) is attached to T1 and T2 when circuit box is completed.

    Step 7 : After all wires are connected, check the continuity at each connection point in the circuit to insure electron flow. (Electron flow is called conductivity, conductance, or continuity) Use a Continuity Tester before you connect any power source to your circuit. This will insure that each connection point makes electrical contact. Do not place the continuity tester’s probes across any components as the power from the Continuity Tester may damage some sensitive components. Use the Continuity Tester only to test your conductance at each bare wire point.

    Step 8 : Build the circuit containment box. See Box Layout Diagrams.

    Step 9 : Attach a 9 VDC battery; follow the Battery Assembly Sheet. Insert the leads from the battery into the anchor as shown on the Block Diagram, negative is attached to female lug and then to switch (S1).

    Step 10 : To check if circuit is functional, connect a bare wire to T1 and T2 the buzzer will sound, then remove the test wire connecting T1 and T2 and press the reset switch S1. NOTE: Use hot glue at each connection point in the circuit to make a more permanent project.

    Step 11 : Your sensor switch can be any switch that allows for the contact of two wires that are connected to the Terminals T1 and T2. The sensor switch can be placed up to 10 feet from the circuit. A standard clothes-pin works well for a simple sensor switch.

    Assessment: Students’ completed circuits. See Project Rubric listed in Materials .

    Useful Internet Resource:
    * National Science Education Standards (NSES)

    Special Comments:
    To create the alarm circuit the teacher would need to purchase the electronic components and wire from any electronic supplier. Styrofoam can be found at a local hardware store. The specialized connectors can be purchased from Abra Electronics Corp ( http://www.abra-electronics.com ). Also, the complete kit is available from Abra Electronics or from Just EASY Educational Kits at http://www.easyecircuits.com

    Teachers: I have constructed this circuit with my students and I am constantly making changes based on their recommendations. Please e-mail me your comments and observations so that I may modify these instructions or if you have a circuit you would like me to create for your classroom use; maybe I can help. Additional graphic aids are available from my web site as well as the Easye connectors, other projects. HANDS-ON is still the best teacher. Please e-mail comments to: eprice@nrtco.net