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Simple IC 555 Oscillator Circuits

Simple IC 555 Oscillator Circuits is a 555 timer chip which common and easy to use.

It is good for many projects.

But for some circuits we must know how it works when not active.

Two main pins:

IC 555 Pinouts

Here is a list that shows what each pin on the chip does.

IC 555 Pinouts Functions:

IC 555 Internal Structural Layout:

555 chip works with power between 16V and 18V.

Pin 3 (output) and pin 7 (discharge) which goes low together inside chip.

Resistor R1 makes pin 7 go high.

Chip gives current in two ways:

Push out (source): 100mA at 5V, 200mA at 15V

Pull in (sink): 50mA at 5V or 15V

Common problems:

Uses more current with around 10mA

Output voltage is little less than power which is up to 2.5V lower

Output voltage little more than ground which is 0.5 to 1.5V higher

Can push 200mA but pull only 50mA

Modes of use:

Astable: Chip turns ON and OFF again and again

Monostable: Chip turns ON for short time after trigger

VCO (Voltage Controlled Oscillator): Timing controlled by voltage signal

ASTABLE MULTIVIBRATOR

Below is a astable multivibrator frequency graph chart that can help us figure out how fast the 555 chip turns ON and OFF.

555 timer chip can act like flasher it turn ON and OFF very fast.

This ON-OFF speed is called frequency.

We can find frequency using special chart or formula.

Astable IC 555 using graph

Chart works only for special circuit setup.

In this setup:

Capacitor charges slowly through two resistors.

When full enough pin 6 sees it and tells pin 7 to empty it fast.

When empty enough then pin 2 sees it and tells pin 7 to stop and then it start charging again.

This keeps repeating and flashes again and again.

A small resistor is added to protect the chip.

It does not change flashing speed.

How to use chart:

Add two resistors like time: 1 hr + 10 hr = 11 hr same for resistors

Find the total resistor value on resistor scale e.g.10,000 ohm = “1” on 10k scale

Draw straight line across chart from that point

See where line meets our capacitor value like 0.1 microfarad

That point shows our flashing speed in hertz Hz

Formula:

There is also a simple math like formula to find flashing speed but chart is faster for quick guess.

Formula:

Frequency = 1.4 / [(R1 + 2×R2) × C]

where:

This formula helps in circuits that blink or flash like timers or LED blinkers.

We can change R1, R2 or C to make blinking faster or slower.

IC 555 Astable Frequency table

555 astable frequencies
CR1 = 1k
R2 = 6k8
R1 = 10k
R2 = 68k
R1 = 100k
R2 = 680k
0.001µ100kHz10kHz1kHz
0.01µ10kHz1kHz100Hz
0.1µ1kHz100Hz10Hz
100Hz10Hz1Hz
10µ10Hz1Hz0.1Hz

Simple Astable

The simplest 555 flasher circuit needs only one resistor and one capacitor.

The chip uses pin 3 (output) to charge and discharge the capacitor.

This makes the blinking (flashing) happen.

Formula:

When 555 timer is in astable mode it makes a continuous square wave like ON-OFF signal again and again

We can find the frequency speed of blinking using this formula:

f = 1.44 / [(R1 + 2×R2) × C]

where:

This design lets the 555 chip blink without stopping.

Low Frequency Oscillators

If we use a special capacitor called electrolytic capacitor instead of regular one then the flashing will slow down a lot.

When it flashes less than once per second then its not a flasher anymore but it becomes a timer or delay circuit.

With this setup the 555 timer can make delays up to 30 minutes.

but for long delays the timing is not very accurate.

Low frequency oscillator 555 delay time chart:

555 Delay Times:
CR1 = 100k
R2 = 100k
R1 = 470k
R2 = 470k
R1 = 1M
R2 = 1M
10µ2.2sec10sec22sec
100µ22sec100sec220sec
470µ100sec500sec1000sec

555 ASTABLE OSCILLATORS

555 timer chip is very useful!

It can make circuits that:

But remember:

SQUARE WAVE OSCILLATOR

Astable Mode:

Monostable Mode:

Bistable Mode:

555 Monostable or “one Shot”

Monostable Configuration:

Falling Edge Trigger:

Set Duration T:

One Shot Circuit:

Conclusion:

Simple IC 555 Oscillator Circuits is a very popular because it is a versatile chip which is easy to use and works in many circuits like for blinking, timing or oscillating.

555 timer is easy and useful it can make lights blink, sounds beep, or delays to happen.

It just uses few parts like resistors and capacitors.

This chip is good for learning and making fun projects.

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