Hi all..I have another dummy electrical questions. I have to buy some more switches and they all reference being SPST or SPDT or DPDT. What does this mean ? I need simply switches that are on/off, rotary 12 position etc. So what should I pick ? SPST or SPDT or DPDT..Any help would be greatly appreciated....thanks alot...JB

SPST- Single pole single throw : single circuit will get pulse in one directionSPDT- Single Pole Dual throw : single circuit will get pulse in both directionsDPDT- Dual pole Dual throw: 2 pole will get pulse in both directions and switch can be used for 2 different circuits.For toggle switches I would go for SPDT. Depending on the interface used to hook up your switches sometimes if you use SPST you will need to flick the switch twice to get a result. For example lights: From the off position flicking the toggle to give you a pulse (L) to turn the lights on. flicking the toggle back wont give you a pulse (L) so in order to turn the lights off you will have to flick the toggle to the on position again. Not very realistic. However with the SPDT toggle switch all you do is run a wire between both lug and that way you get a pulse (L) in the up and down position. As for pushbutton switches you need momentary normally open type. these can be SPDT or DPDT doesnt really matter as you use these to send a sngle keystroke the same as your keyboard.There are other guys in here with much more electrical knowledge than me so hopefully they will give you a better heads up especially concerning the rotary switches as Im still learning about those myself but a 12 position means it has 12 stops and a 3 position will only have 3 stops if you get what I mean.Gaz

"As for pushbutton switches you need momentary normally open type. these can be SPDT or DPDT doesnt really matter as you use these to send a sngle keystroke the same as your keyboard"Sorry I meant to write SPST or SPDTGaz

Here's a sketch showing the different switches.http://forums.avsim.net/user_files/46574.jpgSPST - Single Pole Single ThrowSPDT - Single Pole Double ThrowDPST - Double Pole Single ThrowDPDT - Double Pole Double ThrowTher are also variations within these classes too - for example, a SPDT switch may be listed as either:-ON-ON, meaning that it has two positions, each of which turns one circuit on,ON-OFF-ON, meaning it has three positions, the middle one is OFF, the two outer ones each turn one circuit ON, or(ON)-OFF-(ON) meaning it has three positions, the middle one is OFF, the two outer ones each turn one circuit ON, but the switch won't stay in either of the outer positions (Called a momentary action - the circuit is ON only as long as you hold the toggle in place (or hold a button down)Richard

Nicely done, Richard. Good of you to mention the modes of operation because the variations are useful for different types of things.Also, switches can come with more than two poles if you ever need such a thing.Peter http://bfu.avsim.net/sigpics/PeterR.gifBFU Forums ModeratorRenegade/Seawolf Design Group (RSDG)