Slotted optical switch and Halls

[Oppie]

I've got some old designs that use the H22L2 slotted optical sensor. Used to
be able to get them from Fairchild but they're now phased out. They now only
have phototransistor versions and not the logic output types.

Closest substitutes I found are from Optek. Omron also has some good ones
though in a different form factor. Does anybody have other recommendations?

On a related note, I've also got some Hall effect sensors used for limit
switches with the magnet passing side to side across the sensor face. The
repeatability is not as good as I would like it to be. Any suggestions on
how to improve repeatability? Have been experimenting with a Micronas HAL506
which is high sensitivity, temperature compensated and a chopping amplifier
type so I'm thinking that my problem is more in trying to concentrate the
magnetic field. So far I've been using a 1/8" diameter AlNiCo rod magnet.

Tia - Oppie

 

[Oppie]

Is there no attempt to close the magnetic loop?
That is to say, no attempt to decrease the air gap?

Running with a minimal air gap of .010"
Was thinking of using a steel U channel under the sensor to further increase
the sensitivity.

I probably should also get hold of a linear Hall to see if there are any
other fields that might be biasing the switch. There is a step motor in the
area and I don't know yet how much stray flux comes from it.

Trying to get away from using microswitches for the limits. The precision
has been good, in the order of 50 uM. The Omron optical slot sensors are a
bit larger and more expensive but also had a similar precision.

 

[Oppie]

Extensive report:
http://www.cnczone.com/forums/open_...01878-electronic_home_switches_made_easy.html

Precision: <+/- 0.02mm

A weak magnet with a Honeywell SS441. Weaker magnet => better
accuracy. ISTR some experimenting with magnetic circuits too,
somewhere deep in that thread.

Very nice reference. Thank you!