Scmitt Trigger circuit using NE 555


Apart from the timing functions ,the two comparators of the 555 timer can be used independently for other applications.One example is a Schmitt Trigger shown here. The two comparator inputs (pin 2 & 6) are tied together and biased at 1/2 Vcc through a voltage divider R1 and R2.Since the threshold comparator wil trip at 2/3 Vcc and the trigger comparator will trip at 1/3Vcc,the bias provided by the resistors R1 & R2 are centered within the comparators trip limits.

By modifying the input time constant on the circuit,reducing the value of input capacitor (C1) to 0.001 uF so that the input pulse get differentiated,the arrangement can also be used either as a bistable device or to invert pulse wave forms.In the later case ,the fast time combination of C1 with R1 & R2 causes only the edges of the input pulse or rectangular waveform to be passed.These pulses set and reset the flip-flop and a high level inverted output is the result.


Circuit diagram with Parts list.

Schmitt trigger using ne 555JPG



  • Assemble the circuit on a good quality PCB or common board.
  • The circuit can be powered from a 9V battery or 9V DC power supply.
  • The IC NE555 could be mounted on holder.

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