Is there a frequency meter that works like this

[Cavoli]

I need an instrument that can detect signal errors.
A signal should be able to go from example 100Hz to 400Hz
without error detection but if, say, an rising edge diffs
more than 10% in time compared with the last rising edge
then I will get a beep or a light.
A mobile one would be nice.
Anyone know about such a meter?

 

[schmitt trigger]

You require four building blocks
-A PLL circuit
-A buffer to sample the PLL's VCO voltage
-A differentiator network
-A window comparator to determine whether the voltage from the differentiator has shifted above or below a threshold.

 

[c_mitra]

but if, say, an rising edge diffs more than 10% in time compared with the last rising edge then

I do not understand. Do you mean that the risetime for 10% to 90% (base level) is different from the risetime for 10% to 90% (base level) by +/-10% you want to be signalled. Right?

if yes, then the answer is tough but well, possible.

 

[chuckey]

I think you will have to give us a diagram to demonstrate what you mean by your +10%.
Frank