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I've designed a circuit that relies on the action of momentary pushbuttons as described here:

http://tymkrs.tumblr.com/post/19734219441/the-four-pin-switch-hooking-it-up

Namely, that a 4 pin pushbutton can have two pairs of pins (1,2) and (3,4) such that:

Switch Open: (1 and 2) are a connected pair, (3 and 4) are a connected pair and the pairs are not connected to each other

Switch Closed: (1 and 3) are a connected pair, (2 and 4) are a connected pair and the pairs are not connected to each other

However, after ordering some buttons that then have the alternate (and seemingly more common) operation of

Switch Closed: All pins connected.

I realised the error of my ways.

How would I differentiate these two types of buttons when searching? Does anyone have an example of a component explicitly implementing the button behaviour described above?

[Unfortunately I rushed ahead and already ordered a PCB with a 6mm push button footprint after testing with similar components, excluding the specific button. I'm aware I could implement other solutions, but if someone has an answer to this specific question, it would save me a lot of rework.]

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  • \$\begingroup\$ Those are weird buttons. \$\endgroup\$ – Passerby Dec 7 '17 at 20:34
  • \$\begingroup\$ I think your text description works as a minimum, but you should really upload a diagram if possible. \$\endgroup\$ – Bort Dec 7 '17 at 20:39
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    \$\begingroup\$ I haven't seen a switch that works as your link suggests. You can get DPNO (double pole, normally open) buttons, where there is no connection between any pins when not pressed, and (say) pins 1 and 2 are connected, and 3 and 4 are (separately) connected when pressed. \$\endgroup\$ – Peter Bennett Dec 7 '17 at 20:41
  • \$\begingroup\$ i think that it is a SPDT switch like this one ... amazon.com/6-5mm-Momentary-Tactile-Button-Switch/dp/B07857HLVC \$\endgroup\$ – jsotola Dec 8 '17 at 1:40
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I have been at this for over 30 years and have never seen such a switch. The article you refer to is flawed in its analysis as to how the 4 pin switch works. The circuit has a pulldown resistor pulling a pin, P7 to ground though some resistor R. The resistor and pin being pulled down to ground could just as well be tied to a single pin of a 2 pin switch. When the switch is pressed (closed) the 3.3V is also connected to the other two pins, so that P7 is now pulled up to 3.3V and current also flows trough the resistor to ground. Its just a simple SPST switch with 2 pins on each side of the switch - could just as well be 2 pins. No magic here, but indeed some sleight of hand.

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  • \$\begingroup\$ Thought so! Shame, Coming up with a work around. Thank you! \$\endgroup\$ – Sam Gonshaw Dec 8 '17 at 15:19
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I have not seen what you are looking for out of the box, however...

If you find a "4P2T" (AKA: Four-pole two-throw, or quad-pole double-throw) switch/button, you could do the following with the wiring:

4PDT switch configuration

Let's call state 1 "open", and state 2 "closed".

You may have a difficult time finding a 4P2T switch or button that is momentary though.

Another thing to look out for would be to ensure the switch is a "make before break" style switch, which means the pins are all briefly disconnected from each other while in the middle of switching. Otherwise, you may have issues with shorting.

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  • \$\begingroup\$ Thanks! Having a look around there are some momentary 4P2T switches out there - will go with this for another version. \$\endgroup\$ – Sam Gonshaw Dec 8 '17 at 15:19
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" How would I differentiate these two types of buttons when searching? "

Datasheet, datasheet, datasheet. If the vendor doesn't have a link to one, find another vendor.

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Seems like the part I wanted doesn't exist.

For completeness I include my workaround:

The specific usage desired was the following, where S1 and S3 would switch together.

Intended Operation

So with this desired switch not existing I have a challenge order to implement the same in the same functionality using the 6mm spaced 4 drill holes on my pcb:

PCB

I can use two switches, with two of the pins snapped off that will go in back to back. Throw in some resistors to cross those switches and I get:

Alternate Implementation

And I'll just push the buttons tgether. The switching of OUT1/OUT2 does not have to be simultaneous, so this will suffice.

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