[SOLVED] Clean-up Pulse for RB0 interrupt.

[biboymusic]

Hi,

I need help on cleaning up pulses from my hall effect sensor. The project is a wheel speed sensor.

4 magnets on the wheel hub, 1 hall effect sensor on the front fork. That means, 4 pulses/wheel rotation. However, using a simple program on the PIC to count each pulse gives me unpredictable results. As each magnet passes, I get like 100+ counts, very random numbers. Doing manual interrupts on RB0 perfectly counts pulses, using the hall effect sensor gives me random numbers.

Using a Multimeter on the hall effect output, I get +5v and 0v on each magnet pass. So I think I need to clean up the pulses to perfectly give me 1 count on each pass on the magnet.

Any ideas? OpAmp maybe?

 

[Sudarsan_EDA]

Most commonly Low pass filter is sufficient.I solved this problem in my application with LPF.Place an LPF with suitable RC combination.

 

[biboymusic]

Im not really good with analog circuits. Can you give me a sample schematic for LPF? I presume its a circuit I can put in between the output of the hall effect sensor and RB0 port. Thank you.

 

[Sudarsan_EDA]

it is a very simple circuit the RC values may differ for with application(time constant ,cutoff frequency ).



One simple electrical circuit that will serve as a low-pass filter consists of a resistor in series with a load, and a capacitor in parallel with the load. The capacitor exhibits reactance, and blocks low-frequency signals, causing them to go through the load instead. At higher frequencies the reactance drops, and the capacitor effectively functions as a short circuit. The combination of resistance and capacitance gives you the time constant of the filter τ = RC The break frequency, also called the turnover frequency or cutoff frequency (in hertz), is determined by the time constant:

Cutoff frequency (Fc) = 1/(2 pi RC)

 

[biboymusic]

I actually did that. I've searched google and found out about it. With this filter, would I miss some pulse? I did a 1.5k ohms R and 2.2uF C. I should be able to capture pulses upto 200 pulses/sec. Tested the speed, and at 64 km/hr I am already moving very fast like 100+ km/hr.

Thank you.

 

[Sudarsan_EDA]

Better to give the Sensor speed in RPM & CPT(counts per turn).instead of km/hr.
i used 1.5K & 100nF combination.It might be suitable for your application.But not sure.
i given my circuit RC values

 

[biboymusic]

My C value is so large that I actually miss some pulse on high speed. Reduced to nF values gave me better results. It is working perfectly now. Thank you so much for your help.