Curious how a Hall effect sensor works. The few data sheets I have looked at don't answer my basic question of what happens when the magnet is removed? I am thinking of the sensor usually mounted somewhere on a modern auto engine that times the injection/ignition system.
Is there a sensor that detects when the magnet goes by the sensor? That is, reacts to the magnet, then relaxes when the magnet passes? How does it work on the systems that have "teeth" around the perimeter of the wheel, but missing one tooth to indicate TDC?
I think I need to look at a lot more data sheets to figure this out
mcsman:
Curious how a Hall effect sensor works. The few data sheets I have looked at don't answer my basic question of what happens when the magnet is removed? I am thinking of the sensor usually mounted somewhere on a modern auto engine that times the injection/ignition system.
Is there a sensor that detects when the magnet goes by the sensor?
Yes there are hall effect sensor switches that will create a pulse as the magnetic field approaches and leaves leaves the sensor's head. There are also analog hall effect sensors that generate a variable DC output voltage proportional to how strong a magnetic field it is sensing. Some hall-effect sensor switches latch on when say a 'north pole' of sufficient strength is sensed and will only unlatch when a reversed 'south pole' field is sensed. One has to study a specific hall-effect sensor's datasheet to be sure they are getting one that works for the applications at hand.
That is, reacts to the magnet, then relaxes when the magnet passes? How does it work on the systems that have "teeth" around the perimeter of the wheel, but missing one tooth to indicate TDC?
A hall effect sensor won't work just 'looking' at the face of a gear wheel, as the teeth have no magnetic field. Variable reluctance speed sensors are one kind of sensor that is often used with gear wheels, and they are not based on hall effect devices, at least not the ones I worked on in a oil refinery used on large compressors, turbines, and other rotating equipment.
I think I need to look at a lot more data sheets to figure this out
Datasheets are always your best friend when learning and selecting sensors and trying to match them to your application. Lefty
Hey! Thanx for the link, Chagrin. It was very helpful. It shows that we can get sensors to behave just about however we need them. Now, a little more research to find how to implement this without an actual magnet.
Yes, Lefty, I understand the sensor is not "looking" at the gear wheel. I must have gotten confused with the switching mechanism of a CD ignition system. I know the term "Hall effect" comes up often in discussions of performance ignition and/or injection systems.
Now, tell me about these "reluctance speed sensors." I went out to another forum where they referred to the gear wheel and VR sensor, so I think we are on the right track.
And, to shed some light here, I am considering installing fuel injection on my riding lawn mower. Should make starting easier, maybe make some more power (but who cares, starting is the problem here).
Don't want to invest in a mega- or micro- squirt, or any other commercial, after market injection system, when the Arduino can handle it for a whole lot less money.
Are you going to attempt direct injection (injection directly into the cylinder) or are you squirting into the carburetor intake? If it's the latter and you just need to know engine RPM then it would be simpler to watch the AC frequency of the mower's alternator; to chop the 14V+ output to 5V you can use a linear regulator (see LM317 datasheet for example), a zener shunt, or a resistor divider.
Given that there are more gear teeth than alternator magnets you'd get a more accurate RPM reading with the gear teeth -- but I think that's overkill.
Thanks again, Chagrin! The link above is from the same guy that is my inspiration. First saw his work at Craftsman 12HP Fuel Injection -Project | My Tractor Forum , but that thread is not as complete as the one you gave. Now I understand the situation a bit better and may not need (want) to get involved with timing. That eliminates the whole sensor problem.