Why do some encoders have a momentary switch?

[Kerry]

I've been reading datasheets for rotary encoders, and many have two pins allocated to a momentary switch?  Does this mean the encoder itself can be pressed as a switch?  So this is for use as a dial on some control panel, and the switch can be pressed?  Or is it something else?

Thanks,

Kerry

[Half Shell]

Could just be to "home" the encoders so they know when they have moved to a set position. This way encoders can more accurately determine position, as they can only normally record CHANGE of position. The "home" switch might be there to let the encoders know its start point.

[Kerry]

Hmm, why would that be part of the encoder?  In my experience, the home switch is usually external to the encoder so that "home" is not dependent on the encoder position, but the other way around (you read home from somewhere else, then record the encoder position at that instant as "home").  I can't picture an encoder with a built in switch that functions as a home switch...

[Razor Concepts]

Just a thought - those encoders may be used for old ball mice. Two switches for the two mouse button, and the encoder for the ball.

[Soeren]

Hi,

I've been reading datasheets for rotary encoders, and many have two pins allocated to a momentary switch?  Does this mean [...]

... That you should post links to a few of those datasheets, yes.

[Kerry]

Sure thing...

http://www.bourns.com/data/global/pdfs/em14.pdf

This one says "Standard or high force push switch option" so I assume this is intended to be a switch on a panel...

Maybe this isn't the right kind of encoder?  Is there some kind that is intended for use as motor feedback?  I assume I could make it work anyway...

[Soeren]

Hi,

This one says "Standard or high force push switch option" so I assume this is intended to be a switch on a panel...

Yes, it's for use on instruments and the like and the push switch is just to give you an extra control in the same form factor - one likely use of it would be to switch between 2 (or more) increment modifiers, making it able to go in steps of eg. 1 and 10.

Maybe this isn't the right kind of encoder?  Is there some kind that is intended for use as motor feedback?  I assume I could make it work anyway...

It isn't the right one for motor feedback. You could make it work of course, but it would be a poor solution. It has a max. RPM of 120 and the rotational life at 30 RPM and it's torque that will load the motor is not very impressive in a motor feedback, to put it mildly.
This is a very fine (mechanical) device for the intended purposes, but for motor feedback, you want "eternal" life and zero drag.

A slotted disc and 2 pairs of IR emitter/receiver (2 slotted opto couplers or reflective switches) is what you need, just like in an old school ball operated mouse.
If you only need speed and not quadrature (for rotational direction), one opto-switch is enough.