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PhotoTransistor Problem

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anita1984

New Member
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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MikeMl

Well-Known Member
Most Helpful Member
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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