Frequency and period measurement system

[guravsid]

I want to measure frequency and period of any waveform. I want to build a project using analog and digital components (without using microprocessor and micro-controllers ) i. e. signal conditioning and control unit for period and frequency measurement. Can anyone suggest some ideas ???

 

[barry]

ANY waveform? If it's a complex waveform then it will have multiple frequencies. If you're just looking to measure the frequency of 'simpler' waveforms, you can just use a zero-crossing detector and a counter. When the waveform first crosses zero you start your counter and when the wave crosses zero a second time you stop the counter. The value in the counter is then proportional to the period. Another method is to enable a counter for a fixed amount of time and count the number of zero-crossings that occur during that time.

 

[guravsid]

Pulse widht measurement

How to measure the pulse width of a square wave....????without using microcontroller or microprocessor...

 

[jpanhalt]

Try a low-pass filter and measure the voltage, which will increase as the duty cycle increases.




John

 

[FvM]

How to measure the pulse width of a square wave....?

For a digital measurement, you can use the counter method described by barry in post #2 with modified start and stop criiteria.

An analog pulse width measurement can use a gated ramp generator (integrator).

 

[Tunelabguy]

There is no one circuit that will do the job optimally for all possible frequencies. In every application there is a trade off between accuracy and measurement time. Frequency measurements are more accurate if they are averaged over many cycles. But if you average over too many cycles, it takes too long to make a measurement. For slower frequencies, it is often better to measure the period of one or more cycles and use that measurement to imply the frequency, as in bicycle speedometers. For higher frequencies it is more practical to count cycles over a fixed period of time. For optimal measurements you need to know the range of frequencies that must be measured and the requirements for resolution and response time. Based on these factors, very different optimal designs can result.

 

[guravsid]

How will the counter know where to start and where to stop since input to counter is a square wave and counter will start and stop continuously for infinite time. ???

 

[barry]

How will the counter know where to start and where to stop since input to counter is a square wave and counter will start and stop continuously for infinite time. ???

See post 2.

1) Apply a clock higher than the frequency you are trying to measure
2) Enable your circuit
3) When the input crosses zero, enable the counter
4) When the input crosses zero again, disable the counter.
5) Read the value in the counter
6) Multiply the counter value by the period of the clock--> 1/2 period of your input
7) Repeat as necessary

 

[guravsid]

but how the counter knows that zero crossing detector output has crossed zero....???
which input should be applied to counter for enabling and disabling the counter...???

 

[barry]

but how the counter knows that zero crossing detector output has crossed zero....???
which input should be applied to counter for enabling and disabling the counter...???

Maybe you should read about ZERO CROSSING DETECTORs.

You've stated a very vague requirement.

What's your minimum frequency?
What's your maximum frequency?
Amplitude?
Cost constraints?
How accurate/precise do you need to be?
What's your output? A display? A meter? An array of LEDs?
I assume this is just a project for school, right? Or is it being used for sub-orbital spaceflight?

 

[guravsid]

It is a school project. Frequency range is about 0 Hz to several KHz. Output of counter is given to LEDs.