As shown in the figure, the circuit consists of a limiting comparator circuit and a monostable trigger circuit to increase the functionality of a conventional oscilloscope.
The IC1 voltage comparator compares and corrects the signal from the vertical amplifier and adds it to the trigger terminal 2 of IC2. 555 and R1, RP3, C form a single-stability circuit, and a sawtooth scanning voltage is generated at the 6th and 7th legs. When 555 is triggered by the negative pulse, capacitor C is charged through R1 and RP3. When it is charged above the 2/3VDD threshold level, 555 is reset and C is discharged, and a sawtooth voltage wave is applied to the horizontal amplifier as a horizontal scan.
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