SPST pin configuration

Thread Starter

Manjesh Gowda

Joined Oct 19, 2020
67
Hello fam,

I ordered a SPST switch (Through hole type) from distributors and also download the cad file for PCB layout from the same website. I am now confused with the pin configuration, in the footprints it has 3 holes. Usually the SPST switch has only 2 pins right?. I have gone through the datasheet but I did not understand it completely about the pins because they have the same diagram for SPST and SPDT I suppose.
My question is, if it has 3 pins then what will be the connection if I want to turn ON and OFF the circuit and If it has only 2 pins then which pin should I ignore(delete) in the footprints. I attach the footprints picture and datasheet link with this. Footprints which I downloaded are perfect with the measurements (for 3 Pins). Please let me know if u have any leads on this. Thank you

https://eu.mouser.com/datasheet/2/221/MS-100406-1174115.pdf

spst.PNG
 

MrChips

Joined Oct 2, 2009
22,536
With small toggle switches usually contact is made between the center pin (pin-2) and the side opposite to the throw of the switch. Thus it depends on which side you want to be the ON condition.

If you want LEFT throw to be ON (relative to your drawing above) then use pin-2 and pin-3 and leave pin-1 not connected on the PCB.

If you want RIGHT throw to be ON then use pin-2 and pin-1 and leave pin-3 not connected on the PCB.

In other words still layout for three pins assuming that the 2-pin and 3-pin footprints are the same.
 

Thread Starter

Manjesh Gowda

Joined Oct 19, 2020
67
With small toggle switches usually contact is made between the center pin (pin-2) and the side opposite to the throw of the switch. Thus it depends on which side you want to be the ON condition.

If you want LEFT throw to be ON (relative to your drawing above) then use pin-2 and pin-3 and leave pin-1 not connected on the PCB.

If you want RIGHT throw to be ON then use pin-2 and pin-1 and leave pin-3 not connected on the PCB.

In other words still layout for three pins assuming that the 2-pin and 3-pin footprints are the same.
Lets say I consider pin 1 and 2, In this case do i need to worry about the configuration? for example pin 1 should be connected to supply and pin 2 should be connected to any device (relay or bulb). Or does it work either way. Please let me know
 

ericgibbs

Joined Jan 29, 2010
11,630
hi MG,
Either way will close and open the switch to the relay.
E

BTW: The conventional way, would be to connect the power to the centre pin [2] and the switched device to an outer pin.

Is this the switch you have .?
AAA 1029 12.22.gif
 

ericgibbs

Joined Jan 29, 2010
11,630
Hi MG.
I know what the main question is.:)
But the same answer applies.
Centre pin of the switch goes to the power source and the other pin goes to the device being switched On/Off
E
 
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