This post shows you how to build a simple beeper circuit.
When you press a button, it makes a sound using a special type of electronic circuit called an asymmetric multivibrator.
The sound comes out of a small speaker.
This is a fun project to learn about electronics and sound.
What is a Beeper Circuit:
The Beeper circuit is a simple yet advanced electronic gadget that generates a continuous beeping sound, suitable for alarms or indications in settings like hospitals, police stations or fire brigade stations.
Circuit Working:
Parts List:
| Category | Description | Quantity |
|---|---|---|
| Resistors | 1.5k CFR 1/4 W | 1 |
| 4.7k CFR 1/4 W | 1 | |
| Capacitor | Ceramic 470nF | 1 |
| Semiconductor | Transistor BC547 | 1 |
| Transistor 2N2907 | 1 | |
| Speaker | 8Ω | 1 |
| Power Source | Battery 3V | 1 |
| Other | Push button switch | 1 |
The above beeper circuit operates as an asymmetric multivibrator, generating audible signals through the interaction of two transistors (NPN and PNP) in a feedback loop.
The circuit is initiated by a pushbutton and the audio frequency can be adjusted using a resistor.
Below are explanation of the circuits operation:
Initialization:
- Pressing the pushbutton triggers the circuit initiating the operation.
Initial State (Stable State):
- Before the pushbutton is pressed, the circuit is in a stable state with one transistor turned ON (conducting) and the other OFF (non-conducting).
- Let us assume Q1 (NPN transistor) is ON, and Q2 (PNP transistor) is OFF initially.
Pushbutton Pressed:
- When the push button is pressed, it causes a rapid change in the circuit’s state.
Transition to Unstable State:
- The pressing of the pushbutton turns OFF the initially conducting transistor Q1 in this case and turns ON the initially non conducting transistor Q2.
- This transition results in an unstable state where both transistors are temporarily conducting.
Capacitor Charging:
- As Q2 turns ON the capacitor connected to its collector begins to charge.
- The charging of the capacitor determines the duration of the unstable state.
Transition Back to Stable State:
- Once the capacitor is sufficiently charged Q2 turns OFF, and the circuit transitions back to a stable state.
- Now Q1 is turned ON again and Q2 is turned OFF.
Capacitor Discharging:
- With Q1 ON the capacitor connected to its collector starts to discharge preparing for the next cycle.
Repetition of the Cycle:
- The circuit continues to cycle between the stable and unstable states as long as the pushbutton is held down.
- This cycling generates a series of pulses producing an audible tone through the connected speaker or earphones.
- The resistor R1 in the circuit allows for the adjustment of the audio frequency.
- By changing the resistance of R1 the charging and discharging times of the capacitor are modified, influencing the frequency of the generated audio signal.
Optional Earphone Usage:
- If earphones with an impedance of around 500 ohm are used the circuit still operates similarly, providing audio output through the earphones.
Formulas and Calculations:
You may develop a basic astable multivibrator circuit to make a beeper circuit.
When the push button switch is hit, this circuit will create a square wave signal to drive the speaker and emit a beeping sound.
Calculating Frequency:
For a basic astable multivibrator the oscillations frequency f, can be roughly calculated as follows:
f = 1.44 / (R1+2 * R2) * C
where,
- R1 and R2 are the resistors in ohms
- C is the capacitance in farads.
Use this formula to enter your inputs and get an estimate of the beeping sounds frequency.
In our diagram: R1 = 1.5k, R2 = 4.7k, C = 470nF
So the frequency will be approximately:
f = 1.44 / (1.5k + 2 * 4.7k) * 470 ×10−9 = 1.44 / (1.5 + 9.4) * 470 × 10−6 ≈
1.44 / 11.4 * 470 × 10−6 = 1.44 / 5.358 × 10−3 = 268 Hz
This gives an approximate value of the frequency, which may differ significantly based on the actual values and tolerances of the components.
How to Build:
Identify Components:
- Gather all required components ensuring compatibility with the specified circuit parameters.
Transistor Placement:
- Insert the chosen silicon NPN transistor Q1 into the circuit, connecting it as per the circuit diagram.
- Similarly, place the selected PNP transistor Q2 in the designated position.
Connect Speaker :
- Connect the loudspeaker with a coil impedance of 25 to 40 ohms to the circuit ensuring proper polarity alignment.
Resistor R1 Connection:
- Integrate resistor R1 into the circuit to enable audio frequency adjustment.
- Connect it according to the circuit diagram, considering its role in fine tuning the output.
Pushbutton Installation:
- Install the pushbutton for circuit initialization ensuring a reliable connection to facilitate user friendly operation.
Battery Connection:
- Based on the drain current specifications of Q2 select an appropriate battery and connect it to power the circuit.
Conclusion
Following these detailed construction, you will have successfully assembled a versatile beeper circuit with adjustable audio frequency range offering a unique and customizable audio output experience.
The circuit utilizes the principles of an asymmetric multivibrator to produce audible signals and the inclusion of a pushbutton and resistor R1 adds functionality and adjustability to the generated audio tone.