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PhotoTransistor Problem

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anita1984

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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 ,
:)
 

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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.
 
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