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Author Topic: hello there - help please, how do you do the light sensor limit switch - 3 wires  (Read 11130 times)

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Offline nobby

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hello i am stuck, have these

data sheet -  i think is


3 wires
looking down on it from the top pin

 pin 1 Vcc - dont understand = voltage cc
 pin 2 gnd = ground, ?
 pin 3 Vout = voltage out ?

i cant give it 24v

am i connecting it to mach on limits X++ and X--

is it not possible yo use them

i have them on each end of each axis

itching to play with me new toy but buggered the last one crashing the x home!!


« Last Edit: February 02, 2023, 05:14:45 PM by nobby »

Offline nobby

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on my controller
i have 12 volt out
and the input

i think

i think i get it

pin 1 12 volt in
pin 2 to ground on controller board
pin 3 is the input pin out of switch -  to x++ = = == x++ means either way of x axis up or down, x-- the otehr way and the other switch
so i have 6 ground wires going in

or thats how it would work with a proximetry switch

Offline nobby

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oh - so
the light beam is constantly on when not home.
12v + and ground

when the beam is cut

the input gets triggered
set mach to active high

according to the data sheet that is a 5VDC device with an absolute max of 10VDC. If you've applied 12V its probably toast.

'I enjoy sex at 73.....I live at 71 so its not too far to walk.'
Agree with Craig and its not something that I would use for a proximity or limit switch.
Retired Master Electrician, Commercial HVAC/R Service and lots of Hobbys.
I would be happy enough to use an optical switch for a Limit switch but would not use one for a Home switch.

Of course an optical switch used for any purpose is subject to chips or coolant getting in there and obstructing the phototransistor.
I would presume that anyone using such a device has already thought that through  and judged it not limiting.

Limit switches are obviously mounted at the end of travel and a little inaccuracy, say 0.5mm either way in it's detection point
would be fine, and therefore I would regard opto-siwtches as perfectly adequate, with the proviso above.

A Home switch is all about repeatability and for that purpose I would not use an opto-switch.

As you know Mach when homing travels toward a Home switch and on detection of a switch activation, decelerates to a stop, and then
backs up until the switch de-activates whereon it References the axis. The repeatability then depends very much on the hysteresis of the switch,
that is to say the difference (in distance) between when the switch activates and when it backs up and de-activates.

An opto-switch activates as the interrupt blade advances and partially obscures the light beam entering the phototransistor. Let's assume the
activation occurs at 50% obscuration. Now when the axis reverses when does the switch de-activate...at the same 50%, or more, or less?.
The specifications of opto-switches do not include any hysteresis measurement.

I like Omron (or equivalent from other manufacturers) roller plunger snap action microswitches. They have a well-defined and thereby repeatable switch
activation point and more importantly a defined and repeatable de-activation point and the associated hysteresis, 0.05mm. I have used these as Home switches
on my first mini-mill and more recently both as Limit and Home switches on my new mill. I regularly get better than 0.02mm repeatability without
recourse to Index Homing.


'I enjoy sex at 73.....I live at 71 so its not too far to walk.'
I have done measurements on opto interruptors for clocks and Berth Boman for home switches.  See:

And I attach an article that I wrote for a horological publication.

Bottom line: Boman found they worked very well and my measurements confirm if you use the right type.

« Last Edit: February 07, 2023, 08:20:45 AM by JohnHaine »

Offline nobby

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my 25 year old little mill uses them in a stock set up
i just don't know how to wire them
i think i get it now
12v one side
ground the other
middle wire-once tripped to mach 3
i still dont get if both limit switches on the same axis go to one input
due to if one is tripped the other one cannot be

homing direction
just use a limit switches and not home switches
or use them as home switches?
check on the specs, what I can find of them is that they are 5V devices, you wire them to 12VDC and you'll blow them up.

They can be used as either, or both, Homing and Limit switches, although my preference is for other than Homing switches, not withstanding that they work.

'I enjoy sex at 73.....I live at 71 so its not too far to walk.'

Offline nobby

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my only output on my breakout controller for limits switches is 12v
these will not work
just cobble in some micro switches