Description.

A Schmitt trigger circuit shows two distinct signal input levels for turning the circuit ON and OFF.The difference between the Von and Voff voltages called hysteris Schmitt triggers are useful in conbverting slowly rising waveforms into fast rising ones and in relay like application.

The circuit shown here uses a 741 with positive feedback via R5,R6 and R7 for fast switching.Voltage dividers R8 and r9 set the DC input voltage to the non-inverting input terminal to half the supply voltage.The amount of positive feedback depends on the ratio of R6 and r7.the larger the ratio,the smaller will be the hysterisis shown by the circuit.Potentiometer r2 sets the DC voltage to the inverting input terminal and thus sets the threshold voltage at which the signal will trigger the circuit.The input signal can be applied to either of the two input terminals.

Circuit diagram with parts List .

Notes. 

• The circuit can be assembled on good quality PCB or common board.
• The threshold can be set by varying the POT R2.
• The circuit can be powered from a 9V battery or 9V DC power supply.
• It is possible to raise the power supply up to 24V .
• IC1 must be mounted on an IC base.

Description.

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.

Notes. 

• 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.