555 IC Based Schmitt Trigger Circuit

555 IC Based Schmitt Trigger Circuit is a small project.

It work like comparator and comparator is ON/OFF when input cross the voltage.

Noise make output jump and Schmitt Trigger stop this.

It have 2 limit: high and low.

Input goes high then output is ON.

Input goes low then output is OFF.

Between them there is no change.

This call hysteresis.

Below diagram show top noisy sine input and bottom clean square wave output.

Circuit Working:

Parts List:

555 timer have 2 comparator.

It does timing and also Schmitt Trigger work.

Pin 2 and 6 join together.

R1 and R2 give half Vcc bias.

Threshold trip is 2/3 Vcc and Trigger trip is 1/3 Vcc.

If C1 is small to 0.001 µF then input pulse get separate.

Circuit work like bistable or pulse inverter.

Fast path of C1, R1 and R2 pass only the pulse edge.

Edge set reset and flip-flop output go inverted high.

Formulas:

Inside 555 IC it have 3 equal resistor.

They make two level the upper and lower.

Upper (VUT) = 2/3 Vcc

Lower (VLT) = 1/3 Vcc

For 9V supply is VUT = 6V and VLT = 3V.

If input go above 6V then output is LOW.

If input go below 3V then output is HIGH.

If input is between 3V and 6V then output does no change.

How to Build:

To build a 555 IC Based Schmitt Trigger Circuit follow the below connections steps:

• First collect all parts as in circuit diagram.
• Pin 1 goes to battery negative.
• Pin 2 goes between C2 and R1.
• Pin 3 is square wave which goes at signal OUT and GND.
• Pin 4 goes to +9V battery.
• Pin 5 goes to C1 0.01µF for stability.
• Pin 6 connects between R2 and C2 and other side of C2 goes to signal IN and GND.
• Pin 8 connects to battery positive +9V.

Conclusion:

555 IC Based Schmitt Trigger Circuit is simple project for beginner.

It changes noisy sine/triangle wave into clean square wave.

It work by hysteresis with two trigger voltage.

It is cheap, easy to build, used in wave shaping, digital logic and for noise remove.

References:

555 as a Schmitt Trigger and an ON delay timer?