The materials needed are:
- A piece of cardboard, about 6'' x 6''
- 9 V Battery
- Battery snap connector
- DC Mini Buzzer (Ideally a 9V but if not available resistors can be used to adjust)
- Resistors, size depending on the Buzzer purchased (Use next step to calculate)
- 1 ft of ribbon or string
- Large rubber band or hair tie
- 2-4 push pins
- Hole Puncher
- Alligator clips
Step 1: Preliminary Calculations
The formula for voltage is V = IR with V being the voltage in volts, I being current in amps and R being resistance in ohms.
V = 9 volts
I = Can be found on the package as shown in the image
V = I * R --> R = V / I
45 mA = 0.045 A so:
R = 9 V / .045 A = 200 ohms
Resistor values can be rounded if exact value is not convenient (if you need 180 ohm, you can still use a 200 ohm resistor).
Step 2: Separator
This piece will be referred to as the separator. You won't need it until later in the project but it's easier to have it ready before you need it.
Step 3: Battery
Tape the battery onto the cardboard piece. It doesn’t really matter where everything is placed as long as they are connected in the right order, but if you want to keep it more organized, tape it inside any quadrant (as shown by the dotted square) of the cardboard with the wires facing inward.
Step 4: Buzzer
Step 5: Connecting the Resistor
The wires only need to be touching, but to prevent them from accidentally disconnecting you can go ahead and twist the two wire ends together. You can use your hands or if your having trouble pliers or alligator clips can be used as well.
Step 6: Mounting the Resistor
Step 7: Secure the Clothespin
Step 8: Attaching the Wires
Step 9: Completing the Circuit
Step 10: Testing
If your door alarm does not work remove the separator and:
- Check the connections to the resistor
- Check that the foil is pressed tightly enough against the two wire ends