Here we are going to discuss about a simple timer IC 555 project. The 555 timer IC can be used as an audio amplifier with astable multivibrator configuration. It functions as to carry out pulse width modulation (PWM) of audio signal. Current(I) capacity of 555 timer amplifier is 200mA which is sufficient to drive a small speaker. This simple 555 IC based amplifier circuit is a good substitute for conventional low power amplifiers. The low frequency audio signal is applied to the control voltage pin (5th pin) of 555 for pulse width modulation (PWM) generation. For beginners who want to know ‘what is PWM?’, read simple PWM modulation concept.
Circuit diagram of 555 amplifier
Click on the image for enlarged view
- Power supply
- Resistors (1kΩ x 2; 10kΩ; 47kΩ; 100kΩ; 680kΩ)
- Capacitors (10pF; 0.1µF, 1µF, 10µF x 2)
- Transistor (BC547)
- Timer IC 555
- Condenser mic
- Loudspeaker (8Ω)
- The circuit is based on astable multivibrator circuit using 555 timer IC, the working principle of which we had already posted.
Probe further: Astable multivibrator using transistor with animation
- In the normal mode, we just open circuit the 5th pin (Control voltage pin) of 555 IC. But the most interesting fact we often neglect is that if a low frequency signal is applied to the 5th pin of 555 IC, pulse width modulation starts.
- Here the oscillating frequency of 555 astable is approximately 145 KHz. The discharge time of capacitor C3 via diode 1N4007 is too fast since there is no resistor to discharge.
- The condenser MIC is used as transducer to sense the incoming audio signals and convert them to proper electrical signals.
- The output of the MIC is then fed to the transistor Q1 via a capacitor C1. This capacitor is used to remove the DC component of the signal.
- Resistor R1 provides the necessary biasing to the condenser microphone. And the resistors R2 and R3 gives potential divider bias to BC547 transistor.
- The capacitor C2 and resistor R4 provides negative feedback to the transistor circuit which is essential for amplification.
- The pre amplified audio signal is fed to the control voltage pin of 555 timer astable multivibrator running with 145kHz.
- The process of pulse width modulation starts and as we know the speaker does not respond to this much high frequency, it responses to the usual DC value of the modulated output. Hence the audio signal gets amplified.
Pin outs of timer IC 555 and transistor BC547