Astable Multivibrator (Oscillator) Using a 555 Timer IC

by mandlabs in Circuits > Electronics

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Astable Multivibrator (Oscillator) Using a 555 Timer IC

Cover-555 as astable.jpg
Astable Multivibrator using a 555 Timer IC

In this project, we make an Oscillator using a 555 timer IC in an astable configuration. The circuit will produce a series of high and low pulses, causing LEDs to turn ON and OFF continuously. We will calculate and verify the high and low times of the pulse, as well as the duty cycle. Next, we will connect the timer to a voltage divider and vary the voltage at Pin 5 to generate different tones. Finally, we will use an oscilloscope to analyze various waveforms, including the output at Pin 3 and the charging curve of the discharge capacitor.

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Circuit Explanation:

  1. Pin 1 of the timer is connected to ground and Pin 8 to Vcc. This is how we power the chip.
  2. Pin 2 is connected to Pin 6.
  3. Pin 3 is connected to the positive terminal of an LED. The negative terminal of the LED is connected to one end of a 1k resistor (R3). The other end of the resistor is connected to ground.
  4. Pin 4 is connected to Vcc. This is done to disable the reset pin.
  5. Pin 5 is connected to one end of a bypass capacitor 0.1 F. The other end of the capacitor is connected to ground.
  6. Pin 6 is connected to one end of a 47 F capacitor. The other end of the capacitor is connected to ground
  7. Pin 7 is connected to one end of a 10k resistor (RB). The other end of the resistor is connected to Pin 6. We can say that we have connected a resistor between Pins 6 and 7.
  8. Pin 7 is connected to one end of another 10k resistor, labeled as RA. The other end of the resistor is connected to Vcc.
  9. A 100 F capacitor is also connected across the voltage supply to smoothen it.


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Astable Multivibrator using a 555 Timer IC

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About Poco.001.png

To join Poco Club, here is the link.

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We have further modified to circuit to create different tones. Vary the voltage at Pin 5 using a voltage divider. Detailed steps are available on Poco Club. To join Poco Club, here is the link.

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You will observe that the tone of the buzzer sound can be increased or decreased by rotating the preset. When we change the voltage at Pin 5, the duration of charging and discharging cycles is changed. This leads to a change in the frequency of the pulses, and we can produce different tones.

Detailed steps on Poco Club: link.