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how to read signal from hall effect and magnetic speed sensor on PIC

jerk

Oct 13, 2010
16
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Oct 13, 2010
Messages
16
I would like to read signal from 3 wire hall efect speed sensor and two wire magnetic coil RPM sensor located in wehicle. Speed sensor is an active sensor (uses 12V power supply) and its output signal is digital, while RPM sensor is passive and its signal is AC in a range from 2 - 10 volts. I found some tips about CCP and ECCP and i think the best solution to measure speed and RPM from both sensors would be to use CCP in capture mode. PIC16F1827 offers three CCP modules, plus all three inputs are schmitt triggered so I think there shouldn't be a problem specialy for RPM sensor where signal is not digital.

Since output signal from the sensor is not TTL compatible (not in the 0-5V range) and because I don't want to influence on the C.D.I. readings (change the resistance of the sensor) I was thinking to use MOSFET over NPN. MOSFET as I know are voltage triggered rather than current so there shouldn't be any problems on the wehicle internal electronics.
To convert AC signal from RPM sensor I was thinking to introduce a rectifier diode.

Below is the wiring circuit for both sensors connected to PIC input. Tell me if my approach is correct or suggest me different one.
 

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tweaker

Apr 11, 2012
8
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Apr 11, 2012
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8
In my opinion I think the choice of the mosfet for the hall effect sensor is a good one. When the Hall Effect sensors senses that magnet it will trigger the gate of that MOSFET connecting +5V to the input of the PIC. Of course I thought that the Hall Effect is wired at 12V so when it is triggered it should do the same thing without the need for the mosfet. I could tell you that if you were using the ATMEL micro on the arduino it has a built in analogread function so you could make it do different things at various levels but when you say an AC signal from 2-10V do you mean 2-10V peak to peak, or peak. I mean I am assuming that the voltage tracks the RPMs in that sensor? I am not sure but I don't mind collaborating with you on this because I could be wrong about everything haha.
 

Sid723

Jan 28, 2010
57
Joined
Jan 28, 2010
Messages
57
Are the 'speed' sensor and 'RPM' sensor both tracking each of the drive wheels as they turn? If so, I don't see the need for both on each wheel.

You may want to spin the motor or wheels and check the signal at the PIC inputs to see if they are transitioning within the proper TTL levels. Especially for the 'RPM' sensor.
 
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