OR
Operation:
The input signal is amplified and converted to a square wave by a Schmitt
Trigger circuit. In this diagram the square wave is differentiated and clipped to produce a train of pulses each pulse separated by the period of the input signal.
The time base selector output is obtained from an oscillator and is similarly converted into positive pulses,
The first pulse activates the gate control F/F. This gate control F/F provides an enable signal to the AND gate. The trigger pulses of the input signal are allowed to pass through the gate for a selected time period and counted. The second pulse from the decade frequency divider changes the state of the control F/F and removes the enable signal from the AND gate, thereby closing it. The decimal counter and display unit output correspond to the number of input pulses.