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I am wondering, which signals does a 3-pin mouse switch send. Does it only send

  1. "signalled", and
  2. "non-signalled"

or is it able to differentiate between 3 states:

  1. "clicked signalled",
  2. "unclicked signalled", and
  3. "neither clicked nor unclicked signalled"

Here is a diagram of such an (Omron) switch:

Omron switch diagram

The 3 pins are labelled "COM TERMINAL", "NO TERMINAL", and "DUMMY TERMINAL". What are their purposes? Can they be used to differentiate between the 3 states mentioned above, or only to differentiate between the 2 states mentioned at the beginning?

Here is some further explaination from Omron's website about some of the terms, but I'm afraid that I am unable to understand it: Basic Switch: NO, NC and COM Contact Terminal

To illustrate once more what I am trying to understand: The following image (which I've borrowed from a website and modified) shows an Omron switch in the unsignalled/unclicked state (The metal spring makes contact with the connector at the position indicated by the red line). When it is signalled/clicked state, the metal spring makes contact with a different connector at the position indicated by the green line. The metal spring can also be in between the two connectors and not connect to any of them, but float in mid-air (indicated by the dashed yellow line).

enter image description here

The question is: Can the switch differentiate between all three of these states, and can the user of the switch read out those three different states, or is it only possible to differentiate between 2 states?

I'd ask you to explain with easy terminology, since my background is almost purely software engineering. I have only very little electrical engineering knowledge. Thank you!

Update:

Thanks to the first answer to this question by Andy aka, I am able to state more precisely, what I really want to know:

Does such a mouse switch (or this Omron switch in particular) support short-circuiting two separate circuits so that it allows differentiating between whether the metal spring is currently making contact to the connector at the red line (i.e. short-circuiting the 'normally closed' circuit) or whether the metal spring is currently making contact to the connector at the green line (i.e. short-circuiting the 'normally open' circuit)?

If it did support short-circuiting two separate circuits, a user of the switch could differentiate between 3 different states (short-circuiting red, short-circuiting green, not short-circuiting any => yellow).

If it didn't support short-circuiting two separate circuits, it does only provide two differentiable states, but which ones? Is it
1) short-circuiting red and not short-circuiting red; or is it
2) short-circuiting green and not short-circuiting green?

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  • \$\begingroup\$ The switch is usually designed so that it can't stay in the yellow state. Once it's in the yellow state it flips over straight away to either red or green. \$\endgroup\$
    – user253751
    Jan 31 '20 at 10:20
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I am wondering, which signals does a 3-pin mouse switch send

It is a passive device and it doesn't send signals; it can be regarded as an open circuit (high impedance) or, when activated, a short circuit (low resistance). This means that signals can pass through the switch or, get blocked by the switch.

or is it able to differentiate between 3 states

Usually (mainly unless explicitly designed) it has a normally open contact, a normally closed contact and a common contact. When unpressed the normally closed contact makes a short circuit with the common pin and the normally open pin is open circuit. When the button is pressed, the roles swap over.

The 3 pins are labelled "COM TERMINAL", "NO TERMINAL", and "DUMMY TERMINAL".

It's possible that the dummy terminal does nothing other than provide some mechanical strength when soldered or fixed into place in the target circuit. This dummy terminal would likely replace the normally closed contact.

The metal spring can also be in between the two connectors and not connect to any of them, but float in mid-air (indicated by the dashed yellow line).

Usually this is a transitory situation lasting only milli seconds and cannot be held in this state due to mechanical hysteresis i.e. once the switch starts to move, it flips over fairly rapidly.

Some switches are therefore described as "break before make" or "make before break" and this describes how the contacts connect and disconnect as the switch operates. For instance, make before break devices will connect COMMON to NORMALLY OPEN before breaking with NORMALLY CLOSED.

Can the switch differentiate between all three of these states

The switch is a passive unintelligent device and therefore if you want to know what state it is in you use electronic circuits to make that differentiation. The middle state (half way) is rarely ever used for anything meaningful except in electronic piano keys where the time taken to break then make is used as a measure of how hard a finger has hit a key.

UPDATE

Think of the switch as able to perform this type of analogous fluid flow function: -

enter image description here

  • Water can pass from the common port to the right hand port when the handle is in the position shown. Look at the red arrow
  • When the handle is moved to the opposite position, water can flow following the black arrow.

Back to electricity; the arrows represent flow of electrical current.

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  • \$\begingroup\$ That was really helpful. It allowed me to formulate my question more precisely. May I ask you to take a look at the Update to my question? \$\endgroup\$
    – j00hi
    Jan 31 '20 at 10:37
  • \$\begingroup\$ Think of it using an analogy. The analogy is to do with water and flow and, the switch can be regarded as a diverter with a manual handle. In one handle position, pressurized water can pass from the common port to the normally closed port; with the handle in the other direction the water passes from common to normally open port. In between, water may or may not pass to either. \$\endgroup\$
    – Andy aka
    Jan 31 '20 at 10:42
  • \$\begingroup\$ I have been pondering about your illustration with the fluid flow and what point you are trying to make with it. There will be some position of the water switch where there is some water flowing in BOTH directions, red arrow and black arrow. Does this for the OMRON switch mean that there CAN be a state where there is electrical current on BOTH circuits at the same time (i.e. electrical current on the the circuits marked red and green in my illustration above)? \$\endgroup\$
    – j00hi
    Feb 9 '20 at 8:31
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    \$\begingroup\$ That scenario would be called make before break i.e. the micro switch makes contact with the normally open contact before breaking contact with the normally closed contact. If the valve had a midpoint that’s prevented flow to either left or right it would be equivalent to break before make. \$\endgroup\$
    – Andy aka
    Feb 9 '20 at 10:58
  • \$\begingroup\$ Ah, I see! It's clear now. So the last question that remains unanswered to me is how this specific Omron switch behaves. Can this information be found in its specification? If one wanted to measure its behaviour (i.e. make before break or break before make), how could it be done? \$\endgroup\$
    – j00hi
    Feb 9 '20 at 11:32

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