Chris
Which Hall Effect Sensor are you referring to?
I checked out the Hall Effect Sensor that Parallax offers, but it appears that it requires use of a magnet on the
rotating shaft.
I'm thinking that the sensor that Parallax offers will not sense a screw head.
In the documentation for the http://www.parallax.com/product/605-00005
I've been looking for something that will detect metal like gear teeth or a screw head, but have not been able to find one.
The only thing I've had success with so far is a photo transistor and white duct tape.
I'm sure there is something out there, but both jdolecki and myself are not easily or with much difficulty able to find something
like this.
It appears that component selection from a 50 page Digi-Key catalog no longer exists.
I really miss that.
At least it got you started.
Typically a VR (variable reluctance) sensor is used to detect ferrous objects as you describe -
most cars use at least two to obtain crankshaft and camshaft positions.
The tricky part with a VR sensor is that the output has to be conditioned as
1) their output varies directly with the rpm so can be anywhere from a few 10s
of millivolts to 100+ volts in a sine wave.
2) The actual instant of nearest proximity between the sensor and the moving object
is at the point where the generated sine wave passes zero.
There are various conditioning chips that handle the voltage swings and also
detect zero-crossing and emit a logic level pulse that your microcontroller
can use. I like LM1815 It's pros are that it's cheap, bulletproof and works
very reliably when set up properly. The cons are that it needs a couple of
discrete Rs and Cs. You can get industrial quality VR sensors from your
local auto parts store. I think the one I'm using on a small IC engine was
less than $20. If you need further info I'm around so feel free to ask away.
jdolecki
Posts: 726
Comments
Second thought would be a photo-interrupter depending on the configuration of the output shaft.
I just want to detect the steel set screw on the pulley.
Can the propeller input handle the high rpm input?
Which Hall Effect Sensor are you referring to?
I checked out the Hall Effect Sensor that Parallax offers, but it appears that it requires use of a magnet on the
rotating shaft.
I'm thinking that the sensor that Parallax offers will not sense a screw head.
In the documentation for the http://www.parallax.com/product/605-00005
I've been looking for something that will detect metal like gear teeth or a screw head, but have not been able to find one.
The only thing I've had success with so far is a photo transistor and white duct tape.
I'm sure there is something out there, but both jdolecki and myself are not easily or with much difficulty able to find something
like this.
It appears that component selection from a 50 page Digi-Key catalog no longer exists.
I really miss that.
At least it got you started.
most cars use at least two to obtain crankshaft and camshaft positions.
The tricky part with a VR sensor is that the output has to be conditioned as
1) their output varies directly with the rpm so can be anywhere from a few 10s
of millivolts to 100+ volts in a sine wave.
2) The actual instant of nearest proximity between the sensor and the moving object
is at the point where the generated sine wave passes zero.
There are various conditioning chips that handle the voltage swings and also
detect zero-crossing and emit a logic level pulse that your microcontroller
can use. I like LM1815 It's pros are that it's cheap, bulletproof and works
very reliably when set up properly. The cons are that it needs a couple of
discrete Rs and Cs. You can get industrial quality VR sensors from your
local auto parts store. I think the one I'm using on a small IC engine was
less than $20. If you need further info I'm around so feel free to ask away.