PhotoTransistor Problem

[anita1984]

Hi Forum ,i am using a laser module, phototransistor SFH309-5, and 74HC14N (Circuit in the attachment) to detect the speed of the motor. On the Vout2 i measured frequency up to 2,8KHz when the speed of the motor is 28 000 RPM (because 6 reflected beam every rotation). But when i increase the motor to 32 000 RPM the frequency on Vout2 is 500Hz , and it should be 3,2KHz , what can be the problem ?
Thank you in advance ,

 

[colin55]

What voltage is Vcc?

 

[MikeMl]

R2 looks low to me. Try several higher values up to 20K.
R1 looks low, too. Check that the current through the LED(I doubt that it is a "laser") is within spec.

 

[palmtree]

MAYBE YOU HAVE TO REPLACE R1 BY ANOTHER ONE LARGER to protect the laser module

 

[12345678901234567890]

Are you able to check it (the interuptor module),with another pulse counter?

 

[anita1984]

thanks for all , i change the value of R2 , it's now 10K , it's working well
Have a nice day

 

[palmtree]

congratulations anita