Selecting a new SPST pushbutton switch?

Electromechanical Switches
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1

Hello,

I have a switch that is On-Off and SPST, but uses 2 additional poles (+/-) to illuminate an LED when pressed. See circuit:
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I am looking to purchase a new button that is larger. I found CWI278-ND which meets my needs, however the circuit is slightly different - it only has 1 additional pole for the LED. See circuit:
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I would really appreciate any help - either on how the switch I’ve found could be wired to match replicate the previous switch I have, or how I could find a similarly large switch with an equivalent illumination circuit.

Thanks!

2

Also, I could have incorrectly identified the switch I already have. It would be great if I could get help confirming I properly identified it. Pictures below.

The switch behaves as follows when not plugged into anything:

  • when “pressed” continuity exists between the middle two wires on the connector
  • surprisingly, continuity doesn’t exist on any other wires - specifically the +/- wires which should power the LED…
  • when “un-pressed” continuity does not exist anywhere

The circuit board the switch plugs into has the following properties:

  • when the switch is off / open, there is 12V on the “switch” pins, and 0V on the +/- accessory LED pins
  • when the switch is on / closed, there is 0V on the “switch” pins, and 12V on the +/- accessory LED pins

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3

Hello Sanford78 and welcome to the forum, what are the constraints for the physical size of your switch, it will help us nail down the options available.

Panel size being the most important.

4

Michael thanks for the help.

I’d like the switch to be >16mm in diameter, panel mount would be nice but not required.

My biggest challenge at this point is just identifying what circuit / switch type I currently have.

Some more information:

  • I’m doing a mutlimeter diode test on the switches LED pins, and in both directions it reads OL and powers the LED faintly
  • If I close the “switch” poles, the board goes from 0V on the LED pins to 12V on the LED pins - so it appears that somehow the board switches the LED circuit on…?

If there is anything else I could test to help identify the switch type please ask!

5

It would seem that the switch I’m trying to replace was designed for the LED to be “always on”, and the PCB I’m plugging it into has a circuit that only provides power to the LED when the switch is closed, making it light up only when you press the button.

I’d love help determining if I can use the replacement switch I already identified CWI278-ND as I’m not sure how I’d wire it into the circuit.

6

A lot of the switches in the illuminated side request a specific supply voltage and have a internal cirucit to protect the lighting element when supplied power, either in steady state or during actuation.

CH946-ND Has a circuit that does that, and looks to match the circuit diagram (in function) that you pasted in the opening post.

I think that CWI278-ND actually fits your use case, espically since it allows you to switch the LED function (save LED ON when circuit is off, that one is a touch more rare in the catalog).

7

Thanks Michael - good to know I’ve selected the best option already.

Appreciate your help!