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Magnetic sensor interface

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rayhall

Member
I am designing a circuit that will convert the signal from a magnetic (reluctor) sensor as used on engines to read crankshaft position.

This circuit works, but there are some problems. It is far too sensitive and can read the signal from the sensor when it is 100mm from the teeth on the crankshaft trigger. The sensor is normally 1mm from the teeth.

I need to modify the circuit so it will not read any signal that is less then 500mv and have a hysteresis. I need any signal that goes over 500mv and then crosses zero to be seen as a good signal.

Sorry if I do not have the correct jargon. My background is automotive not electronics.

Ray.

**broken link removed**
 

Dx3

New Member
First, R9 is responsible for decreasing sensitivity. Lower the resistance in R9 to lower the sensitivity.
Second, forcing "ignore" to 500 millivolts can be accomplished by making a voltage divider that sets pin 3 at 500 millivolts above pin 2.
Third hysteresis is accomplished by adding a resistor from the output to the non-inverting input (pin 3).
The bias circuit for "ignore" will contribute to reducing the sensitivity by wasting some of the signal.
These things are interactive. I could not do the math from here.
 

crutschow

Well-Known Member
Most Helpful Member
I do not see any DC path to ground for the 100nA (max.) input bias current of the LM193. There needs to be a resistor (say 100kΩ) connected from one of its inputs to ground to provide that path.
 
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MikeMl

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rayhall

Member
I have changed the circuit to add the 500mv offset, and that works. Does R4 also provide the input bias current. I have not done anything with the hysteresis.

Ray.

**broken link removed**
 

crutschow

Well-Known Member
Most Helpful Member
I have changed the circuit to add the 500mv offset, and that works. Does R4 also provide the input bias current. I have not done anything with the hysteresis.
R4 does indeed provide a path for the bias current.
 
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