Astable 555 Oscillators

A Collection of Oscillators using 555, these are Astable circuits. You can observe a square wave at the output and a ramp waveform across the capacitor. 

The Astable Configuration is like an Oscillator with a Square wave output. You can adjust the Frequency and Duty Cycle (means off time and on time pulse width as a %). The variation is done by playing with the caps and resistors while looking in One Eye at the Sacred Formula.



Astable 555 Tutor - This is a demo of the popular 555 timer. you can try out the project on this page by a javascript simulation.


The 555 Astable oscillator gives a square wave output at pin 3, The output drives two LEDs, LED1 lights up when pin 3 is low and LED2 when pin 3 is high.

The 555 can source (LED2) or Sink (LED1) upto 200mA. It can even drive a small motor or lamp with diodes added to protect from inductive kickback. Vary Ra, Rb and Ct and see the change of frequency, period and duty cycle.



Running Lights with 555 and CD4017 - The 555 Astable generates a clock for this circuit, an oscillator giving a square wave output at pin 3 which is counted by 4017 to give a running lights effect.



The frequency of oscillation of astable 555 is given as f = 1.44 / ((R4 + 2 * (R2 + R3)) * C3)



Here is another design, a dual 555 multivibrator like power oscillator. This is my contraption and conception but couple of decades old. It appears to have errors. It worked but the document fixing after design worked, not done. This can be used to make a small inverter, for powering 230V gadgets of low power. The transformer is used in step-up mode. It may make a sound if the laminations are not of good quality.



This circuit can be modified using 7555 and switching transistors like BD139 driving a Ferrite 100 kHz transformer to build a Fluorescent Lamp of 10W to 20W.

555 Maximum Frequency

555 can Oscillate upto 300kHz. It is better to not cross 200kHz as it is not stable at Higher Frequencies with change in Temperature. CMOS version 7555 can move upto 1 Mhz speed. These may be fast versions today. Keep sensitive chips like Opamps and Timers and related parts far form hot components like Regulators and Transformers.

Dual Astable On-Off Oscillator

Here is a simple Dual Astable using 556 which has two 555 packed in one big chip. The R_L resistors could be LED Arrays to make decorative Flashing Lights for bikes. The R_L resistors could be Coils of a Push-Pull Transformer to create a small Inverter or Step-Up Voltage Convertor.

Images above are from the Original Signetics 555 Datasheet

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