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[Reply #30 on:]

One technique I sometimes use is to turn on a 50% duty cycle PWM pin, and hook that to the input I'm testing.
May be a bit fast for this application, but at least it will show transitions.

[Reply #31 on:]

@ AWOL

One technique I sometimes use is to turn on a 50% duty cycle PWM pin, and hook that to the input I'm testing.
May be a bit fast for this application, but at least it will show transitions.

That is  a good idea AWOL, use the Arduino to generate a pulse. Or a 555 astable circuit set the the frequency you want. Or a second Ardiuno.  That way, it will check the "counter program""

@ robtillart

I am interest in this topic because it can be use a way to measure RPM ( ex : on a fan - using LED, Laser LED , IFR LEd ) or frequency counter. I will look at the "Sampling Routine" how you do it.

PS : This Forum is an exellent place to share ideas.   

[Reply #32 on:]

A. Check the sensor with voltage to check if it have a 0 V for LOW and a 5 V for HIGH.
    If not well the system will not work.

The output voltage of the sensor is 2.5V.
Is that the problem??

[Reply #33 on:]

The output voltage of the sensor is 2.5V.
Is that the problem?? smiley-confuse smiley-confuse

yes, there should at least be 2 voltages one for LOW and one for HIGH. and if 2.5V is the HIGH it might be well too LOW.

amplify the signal with a transistor ...

[Reply #34 on:]

The output voltage of the sensor is 2.5V.
Is that the problem?? 

How are you measuring that, while the signal is actively changing and using a DVM meter? If so that's not a true representation of the signal, use of a scope would be the only method to determine the active low and high voltage levels if the signal is changing.

Lefty