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Interfacing pick-up sensor

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yehdev_cc

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hi,
I'm designing a circuit to interface a pick-up sensor to microcontroller.
a pick-u sensor - for the people who might not know it - generates an AC voltage that is proportional to the speed of a moving metal body near the it ( the sensor ), using a magnet, i.e, it functions as a generator.
whatsoever, I used the following circuit (in the attachments) to interface it to a PIC microcontroller, as square pulses, then determining the speed depending on the number of pulses received in a predefined interval of time.
The problem is that the output is always high (5 volt), so no pulses.
any ideas ? thanks in advance ...
 

Attachments

  • ac-to-pulse.png
    ac-to-pulse.png
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Have you looked at the sensor output on a scope? I have seen sensors used for speed pickup that output pretty high voltages as well as those that output about 200 mV. Do you have a data sheet link for the sensor being used?

My first choice for a sensor (if given a choice) would have been to use one with on board signal conditioning and a TTL output. That would allow direct coupling to the uC.

Pin 3 of your TL081 goes to the diode anode, where does it also go? (U2 pos ip)?

rON
 
Hi,

if nothing else helps try this:

Regards

Boncuk
 

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  • MAG-PU.gif
    MAG-PU.gif
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This one works for output pulse amplitudes greater than about 100mV. Self limiting.
 

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  • AN50.png
    AN50.png
    61.3 KB · Views: 339
Thank you very much for the replies ...

Have you looked at the sensor output on a scope? I have seen sensors used for speed pickup that output pretty high voltages as well as those that output about 200 mV. Do you have a data sheet link for the sensor being used?

My first choice for a sensor (if given a choice) would have been to use one with on board signal conditioning and a TTL output. That would allow direct coupling to the uC.

Pin 3 of your TL081 goes to the diode anode, where does it also go? (U2 pos ip)?

rON
The first problem is that i don't have a datasheet of it, but output voltage didn't exceed 4 volt, I should take another reading while it's working at its highest speed.

The second problem is that I don't have a good variety of ICs here where I live, so I'll most probably have to make the sensor interfacing myself using common ICs and components like diodes, transistors, opamps and microntrollers.

Pin3 doesn't go elsewhere, it's connected only to the diode, just to overcome any noise that might cause the -ve input to raise above the +ve one.

Hi,

if nothing else helps try this:

Regards

Boncuk

thanks alot.
unfortunately, I couldn't quite understand the idea and its parts.

This one works for output pulse amplitudes greater than about 100mV. Self limiting.

Thank you very much, I think your circuit should work well for me.
I'll write a feedback here once I try it and succeeds.
regards.
 
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