Switches
A quick tutorial on switches: They classify switches by the number of "poles" and the number of "throws". (Note that "poles" in this context has nothing to do with filters.) The number of "throws" is the number of lever or button positions in which the switch completes a circuit. The simplest switch is a "single pole single throw", which has two contacts. When the switch is on, it completes the circuit between the two contacts; when the switch is off, it's open. A "single pole double throw" switch has three contacts and two "on" positions. If you name the contacts 1, 2, and 3, and 1 is the common, then in one position the switch completes a circuit between 1 and 2, and in the other position it completes a circuit between 1 and 3. If it's a toggle switch it may be specified with a "center off" position in which it makes no circuit.
A "double pole" switch is basically two separate switches connected to the same lever or button. The "double pole double throw" is pretty widely used. It has a total of six contacts -- a 1, 2, and 3 for each half of the switch. There is no connection between the two halves.
Some catalogs describe the positions of a switch using a different notation, for example, a single-pole single-throw switch is described as "on-off" and a double throw is described as "on-on". A double throw with a center off is "on-off-on". If the switch is spring loaded in one position, such that it snaps back when released, that position is shown in parentheses, so a "on-off-(on)" is a double-throw switch with center off and one of the on positions spring-loaded.
If you need a switch with more than three selections, you need a rotary switch. Rotary switches usually have 6, 8, or 12 on positions; it's possible to get double-pole rotaries which basically are two switch bodies on the same shaft. Most rotaries have a stop mechanism you can set so that if your circuit doesn't use all of the available positions, you can prevent it from being turned to the unused positions.
A "double pole" switch is basically two separate switches connected to the same lever or button. The "double pole double throw" is pretty widely used. It has a total of six contacts -- a 1, 2, and 3 for each half of the switch. There is no connection between the two halves.
Some catalogs describe the positions of a switch using a different notation, for example, a single-pole single-throw switch is described as "on-off" and a double throw is described as "on-on". A double throw with a center off is "on-off-on". If the switch is spring loaded in one position, such that it snaps back when released, that position is shown in parentheses, so a "on-off-(on)" is a double-throw switch with center off and one of the on positions spring-loaded.
If you need a switch with more than three selections, you need a rotary switch. Rotary switches usually have 6, 8, or 12 on positions; it's possible to get double-pole rotaries which basically are two switch bodies on the same shaft. Most rotaries have a stop mechanism you can set so that if your circuit doesn't use all of the available positions, you can prevent it from being turned to the unused positions.