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I want to remove unwanted signal at particular time from the input signal. But I am not sure how to start this. I used capacitors to reduce the unwanted signal. It worked OK, but not well.

By seeing the below image you may understand my problem:

enter image description here

  • The above image is output of the hall sensor.
  • Before the on & off time of single wave, there is a small square wave.
  • How to remove that small square?
  • I used capacitors but I don't know how to use the capacitor to remove or reduce the extra wave (1ms of square wave).
  • I need to measure the RPM of motor using the hall sensor. In order to measure, I used a hall sensor to capture the frequency. But the hall sensor output is not good.

Drawn diagram

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    \$\begingroup\$ Maybe tell us why you need rid of this pulse? How are you interfacing with the hall sensor? \$\endgroup\$ – loudnoises Aug 6 '19 at 7:57
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    \$\begingroup\$ Since the pulse looks very consistent, maybe look at the thing the halls sensor picks up. \$\endgroup\$ – Jeroen3 Aug 6 '19 at 8:04
  • \$\begingroup\$ I second what loudnoises says: instead of just stating what you want to get rid of, tell us what you need to preserve – sounds more promising towards a solution! \$\endgroup\$ – Marcus Müller Aug 6 '19 at 8:40
  • \$\begingroup\$ @MarcusMüller... Since there are three different square wave of different time. i cannot able to measure the frequency of hall sensor. \$\endgroup\$ – Bud Aug 6 '19 at 10:15
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    \$\begingroup\$ We cannot read your mind. We cannot know what your graph shows with certainty if you do not tell us. You mention a MOSFET ONCE in a comment. You have not shown us a circuit. || If you want good quality help you need to provide good quality input. If you showed us the overall circuit and described the mechanical arrangement in adequate detail we could probably help. As per my answer - you probably have noise on the hall signal - you also may have "mechanical motion noise. \$\endgroup\$ – Russell McMahon Aug 6 '19 at 10:57
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I agree with the comments by loudnoises, Russell and Marcus; you really should fix the source of the glitches. But, if you want a band-aid solution, you could add a glitch filter. But, be aware that this will only work for a limited range of RPMs. If the glitches get wider at low RPMs, it won't work. And at higher RPMs the filter will remove the signal, not just the glitches.

The second inverter isn't really necessary, but it makes it easier to interpret the graph.

schematic

simulate this circuit – Schematic created using CircuitLab

enter image description here

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  • \$\begingroup\$ Than you sir i will try this one. \$\endgroup\$ – Bud Aug 7 '19 at 6:04
  • \$\begingroup\$ @Mattman....It works good by using schmitt trigger. You are a genius man. \$\endgroup\$ – Bud Aug 19 '19 at 6:03
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Your hall sensor waveform looks wrong in other ways as well.

At constant RPM, the square waves should be close to 50% duty cycle and should be 90 degrees out of phase. Neither of those are present in you case.

Even if you get the 'pulses' removed, your yellow rising edge is very close to the green rising edge. That will cause havoc in determining the direction. It just will not work!

The cause of your erratic signal is that the hall sensor itself is not working properly. You are trying to correct the digital output but that is too late. You should try to get to the source.

As Russel McMahon said: check your hall sensor, voltage, supply current, noise on the supply etc. Something is not right as these things should work even at very low RPMs.

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  • \$\begingroup\$ Friend don't compare the yellow with green signal. 1,Yellow=hall sensor 2,Green=mosfet gate. \$\endgroup\$ – Bud Aug 6 '19 at 10:16
  • \$\begingroup\$ Supply voltage & current are all ok. I think hall sensor is not proper in my motor. I use CYM 120 Chinese motor, only that motor contains the hall sensor output like this. Hall sensor output of other motors (not CYM 120) looks good. \$\endgroup\$ – Bud Aug 6 '19 at 10:20
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    \$\begingroup\$ @Bud: All that information needs to go into your question. Add a caption under the scope screengrab. \$\endgroup\$ – Transistor Aug 6 '19 at 13:26
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The probable cause is that you have a relatively slowly rising signal edge (magnetic field change) that has noise on it (electrical or mechanical) so that it crosses the trigger level several times as it rises or falls. The sensor orientation may matter. Changing its angle relative to the magnet that it is detecting, or rotating it 120 degrees along its magnetic axis may help. Or not.

The Chinese sensor SHOULD be "good enough". Check power supply filtering to it. Is that a polled sensor or always on? Please provide a datasheet link.

What voltage is the Hall switch working on? Presumably the signal range and power supply voltage are about the same.

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  • \$\begingroup\$ Supply voltage & current are all ok. I think hall sensor is not proper in my motor. I use CYM 120 Chinese motor, only that motor contains the hall sensor output like this. Hall sensor output of other motors (not CYM 120) looks good \$\endgroup\$ – Bud Aug 6 '19 at 10:21

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