With some modifications, the frequency counter can be converted into a Time meter. It is an instrument to measure time. The block diagram of a time meter is shown below:
It shows the construction of an instrument that is used to measure the period of any waveform. The unknown signal is passed through an amplifier to produce a periodic waveform that is compatible with TTL circuits and is then applied to a JK flip-flop. The output of this flip-flop is used as the Enable gate signal since it is high for a time ‘t’ that is exactly equal to the time period of the unknown input signal.
4 Digit Time Meter:
The logic diagram of the 4 Digit Time Meter is shown below:
Here, a 1 MHz clock oscillator signal is divided into 100 kHz, 10 kHz, and 1 kHz time base signals using a 4-stage frequency divider. Any of the time base signals can be connected to the clock input of AND gate using a rotary selector switch. The unknown input signal is divided in frequency by a factor of 2 using a JK flip flop so that the ON time of the ENABLE signal is equal to the period T of the unknown input signal.
When the ENABLE signal is HIGH, the clock pulses are passed through the AND gate and act as the clock input for the 4-stage counter and the counter advances its value. When the ENABLE signal becomes LOW, the counter ceases its operation. Simultaneously, the LOW to HIGH transition at Q’ strobes the counter value into the latches. Also, the HIGH to LOW transition at ENABLE signal triggers the one-shot and it resets the counter value to 0000 so that it gets ready for the next cycle of period measurement.