Indexinf a POV display

cavelamb

I'm really stuck on this.
I need a way to index the POV ceiling fan display but I don't know enough about
modern sensors to to figure it out.

I originally thought IR LED, but I'm using the IR LED for a remote control input.

Hall effect sensors have become vastly more complicated since my days.
Most of them seem overly complicated, which would likely lead to very complicated
code.

All I need to do is mark a position in the rotation as a starting point with
rotation rate of maybe 300 rpm?

But without an index position the display is unreadable by anything but a fast camera.

I need maybe up to an half an inch of clearance minimum.

Open to anything that might work here!


http://forums.parallax.com/showthread.php/141621-QuickStart-POV?p=1116507#post1116507
http://forums.parallax.com/showthread.php/143150-Position-Index-Sensor?p=1135378#post1135378
http://forums.parallax.com/showthread.php/142324-hall-effect-sensors

lanternfish

A quick google search came up with a huge number of similar projects. Maybe you could look through them and find a index sensor that suits your needs.

cavelamb

As best I understand it, because of the rather large air gap requirement,
it looks like this would have to be a ratiometric sensor.
Optek OSH3150U, for example. That's a 5 volt part (4.5vDC minimum)

For that part, the quiescent output is centered half way between supply rails and goes High or Low
depending on polarity of the magnetic flux.

So bring the output to a prop pin through a current limiting resistor.
But then what?

Watch for a solid 1 state (south pole) or 0 (north pols) and build the
magnet stack strong enough to make a valid logic state?

JasonDorie

Why not use something like this: http://www.sharpsma.com/webfm_send/1275

Then take a little tab of metal from a soda can or something, bend it into an L shape, stick it to the back of the fan, shaft, or whatever you have access to, and use the L shaped piece of metal to break the beam, instead of trying to use the fan blades themselves?

Scroll about 1/2 way down this page to see an example: http://ch00ftech.com/2013/02/19/small-improvements-on-the-longboard-wheel-display/

cavelamb

JasonDorie wrote: »

Why not use something like this: http://www.sharpsma.com/webfm_send/1275

Then take a little tab of metal from a soda can or something, bend it into an L shape, stick it to the back of the fan, shaft, or whatever you have access to, and use the L shaped piece of metal to break the beam, instead of trying to use the fan blades themselves?

Scroll about 1/2 way down this page to see an example: http://ch00ftech.com/2013/02/19/small-improvements-on-the-longboard-wheel-display/

Nice link. Thanks Jason.
My first thought was If only I could.
This is on a ceiling fan. Not a custom built machine.

No way it could hold that kind of tolerance with just taped on parts...
But? What I've done so far hasn't worked well enough.

Maybe it's time to try something completely different?

This project uses a Quickstart board as the POV display.
When spinning up and slowing down I've noticed periods where the display
and fan speed match pretty well and the display can be read by eye.

I have a working IR remote link on that board.
I was going to use it to change the messages displayed.

Maybe using the remote to modify the dot timing rate and character width of the POV code could work??
I doubt it would ever sync up solidly.
But might be more readable?

cavelamb

JasonDorie wrote: »

Why not use something like this: http://www.sharpsma.com/webfm_send/1275

Then take a little tab of metal from a soda can or something, bend it into an L shape, stick it to the back of the fan, shaft, or whatever you have access to, and use the L shaped piece of metal to break the beam, instead of trying to use the fan blades themselves?

Scroll about 1/2 way down this page to see an example: http://ch00ftech.com/2013/02/19/small-improvements-on-the-longboard-wheel-display/

On the other hand....
That paper did lead to a couple of new parts. Including this one...
http://sensing.honeywell.com/index.php?ci_id=50322

Volts = 3.8 to 30 VDC
Sinks up to 20 ma.
Rise and fall time - 1.5 uSec max
sets at 25 gauss
release at 5 gauss

That has possibilities...