The IC 555 chip is super useful for many things.
Normally it is used for timing circuits, but this project is a bit different.
In this experiment, we are going to use the IC 555 to make a microphone amplifier.
First, a microphone picks up your voice.
Then, a transistor like a tiny switch gives it a little boost.
Finally the IC 555 chip gives it an extra push to make it even louder.
What is a IC 555 Amplifier Circuit:
The IC 555 can be used as a timer, oscillator or pulse width modulation circuit but it is not typically used as a standalone amplifier.
The IC 555 is more commonly employed in timer and pulse generation applications.
However, it is possible to use external components to configure the IC 555 as a voltage comparator and build a simple amplifier circuit.
This approach is less common and is not the primary purpose of the 555 IC.
Circuit Working:
If you want to use an external music signal with the above 555 amplifier circuit then you can modify the above design as given in the following diagram:
Parts List:
| Category | Component | Quantity |
|---|---|---|
| Resistors | 10k CFR | 1 |
| 330Ω CFR | 1 | |
| 1k CFR | 1 | |
| 680k CFR | 1 | |
| 100k CFR | 1 | |
| 47k CFR | 1 | |
| Capacitors | 0.1μF | 1 |
| 10μF | 2 | |
| 1nF | 1 | |
| Semiconductors | Transistor BC547 | 1 |
| IC 555 | 1 | |
| Electret Microphone | 1 | |
| Others | Speaker 8Ω | 1 |
To use the 555 IC as an amplifier, a specific configuration is essential.
In this experiment, the IC is set up in astable mode without a discharge pin connection eliminating the discharge function through the internal transistor.
The pre-amplified audio signal from the source is then applied to the control voltage pin.
By introducing an external voltage to the control voltage pin, the internal reference voltages of the 555 IC become modulated.
This external voltage supersedes the internal voltage divider network directly influencing the timing of the 555 and causing changes in the output pulse width.
The application of an external voltage to the CV pin proportionally affects both the threshold and trigger levels providing more precise control over the timing characteristics of the 555 IC circuit.
In the absence of an audio input, no voltage is present at pin 5, causing the IC 555 to produce pulse frequencies above 60kHz, which are not audible through a loudspeaker.
When an audio signal is introduced, pin 5 receives voltage, subsequently altering the output pulse width.
This modulated pulse width signal can be reproduced as sound through the loudspeaker.
Understanding the electret microphones functionality is crucial to this setup.
Comprising a diaphragm and a backplate made of conductive materials a small air gap acts as an insulator forming a capacitor.
When sound waves impact the diaphragm its movement alters the capacitance between the diaphragm and the backplate.
This change converts the sound wave into an electric audio signal.
Given the low amplitude of the output audio signal pre amplification with Transistor BC547 becomes necessary.
Formulas:
The following formulas apply to the astable multivibrator setup, which is frequently used for oscillation:
Oscillation Frequency (f):
f = 1.44 / [(R1 + 2 * R2) *C]
where:
- f is the frequency of the output square wave in hertz Hz
- R1 and R2 are resistors in ohms Ω connected as shown in the specific circuit diagram
- C is the capacitor in farads F connected as shown in the specific circuit diagram
Pulse High Time (thigh):
thigh = 0.693 * R1 * C
where:
- thigh is the duration of the high portion of the output square wave in seconds (s)
Note:
These formulas offer a place to start when creating a simple oscillator circuit with a IC 555.
Circuit Construction:
- Place the 555 IC on the PCB.
- Connect pin 8 to the positive supply of the PCB.
- Connect pin 1 to the ground supply of the PCB.
- Connect pin 6 to pin 2 using a resistor R1.
- Connect pin 6 to pin 7.
- Connect a capacitor C1 between pin 6 and the ground supply.
- Connect the positive terminal of the condenser microphone to the collector of transistor BC547.
- Connect the emitter of transistor BC547 to the ground supply.
- Connect the base of transistor BC547 through a resistor R2 to the positive supply.
- Connect the junction of the resistor R2 and the base of Transistor BC547 to the output of the condenser microphone.
- Connect pin 3 of the 555 IC to the positive terminal of the loudspeaker.
- Connect the negative terminal of the loudspeaker to the ground supply.
- Connect pin 8 of the 555 IC to the positive supply.
- Connect pin 1 of the 555 IC to the ground supply.
- Apply power to the circuit through the power supply.
- Speak into the condenser microphone and observe the sound reproduction through the loudspeaker.
Conclusion:
In conclusion, leveraging the 555 IC as an amplifier in this unique configuration offers an interesting approach to audio signal modulation and amplification.
The construction details provided ensure a comprehensive understanding of the experiment allowing enthusiasts to explore the potential applications of this setup in various audio related projects.