Light Activated Alarm With Speaker ( Future Kit )

The device in the picture is a light-activated alarm kit, also called a future kit. It is a small electronic project that can detect changes in light and make a sound when triggered. The kit uses a light sensor to monitor brightness, and when the light goes above or below a certain level, it sends a signal to a speaker to produce an alarm. It helps you understand basic electronics, sensors, and alarm systems, and it can also be used in real life for security or automatic alerts, like warning when someone enters a room or when light conditions change.

Components:

Power

1. Power supply (battery / DC source)
2. Circuit board
3. Wire
4. Solder
5. 4× Pin (connectors)

Input / Control (sensing & switching)

1. Trimmer Potentiometer
2. Photoresistor (LDR)
3. 7× Resistors
4. 2× Diodes
5. Transistor (9012)
6. Transistor (C418)

Output / Support (signal shaping & response)

1. Speaker
2. LED
3. Ceramic Capacitor
4. Capacitor (4.7μF)
5. 2× Capacitors (22μF)
6. Capacitor (0.1μF)

Other

1. future kit box (fb15)

This circuit is a light-controlled sound oscillator powered by a 9V battery. At the input, a photoresistor (LDR) senses the amount of light falling on it. Its resistance changes with brightness, and together with a potentiometer, it adjusts the sensitivity of the circuit. These changes affect the voltage reaching the first transistor, which works as an oscillator to generate a repeating electrical signal at an audio frequency. A network of resistors and capacitors sets the bias and timing, ensuring the oscillator runs at a steady pitch. The signal is then sent to the second transistor, which acts as an amplifier, boosting the weak oscillations so they are strong enough to move the cone of the 8-ohm speaker. Finally, the speaker converts the amplified electrical oscillations into sound waves, so the tone you hear depends on both the light level and the potentiometer adjustment.

1: The photoresistor (LDR) senses light; its resistance changes with brightness.

2: The potentiometer (VR100K) adjusts sensitivity.

3: Resistors and capacitors provide biasing and timing.

4: The first transistor (C458) acts as an oscillator, generating an audio tone.

5: The second transistor works as a power amplifier, boosting the signal.

6: The speaker (8Ω, 0.25W) converts the oscillation into sound.

1: Collect all parts: board, resistors, capacitors, transistors, LED, switch, speaker, battery, wires.

2: Look at the board labels: R = resistor, C = capacitor, Q = transistor, + / - = power.

3: Put in the resistors first, solder, cut extra wire.

4; Add small capacitors, solder, cut.

5: Place the LED (long leg = +, short = −), solder.

6: Put in the transistors, match the flat side, solder.

7: Add big capacitors (stripe = − side), solder.

8: Solder the speaker wires to the SP pads.

9: Solder the battery wires: red to +, black to −.

10: Connect the switch to the red wire.

11: Check all parts and solder joints.

12: Connect the 9V battery, turn on switch, test sound.

1: Mark where the switch and photoresistor will go on the board.

2: Choose the correct drill bit for the size of the switch and photoresistor.

3: Carefully drill the two holes at the marked spots.

4: Insert the switch and photoresistor into their holes.

5: Apply glue to the back of the speaker.

6: Stick the speaker in its place and hold it until it sets.

7: Once all parts are secure, close the casing and screw it shut.

Power & Control

1. Battery (9V) – gives power to the whole circuit.
2. Switch – turns the power on and off.
3. Wires – connect the parts so electricity can flow.

Components on the Board

1. Resistors – slow down the electric current so parts don’t get too much power.
2. Capacitors – store and release small amounts of energy; help set the timing of the sound.
3. Transistors – act like electronic switches and amplifiers; they make the weak signal strong enough for the speaker.
4. LED – lights up to show the circuit is working (in some kits).

Output

1. Speaker – changes the electric signals into sound that you can hear.
2. PCB (Printed Circuit Board) – holds all the parts and connects them with copper paths instead of wires.