Spectrum Software
Industrial Strength Simulation




Spectrum Software has released Micro-Cap 11, the eleventh generation of our SPICE circuit simulator.

For users of previous Micro-Cap versions, check out the new features available in the latest version. For those of you who are new to Micro-Cap, take our features tour to see what Micro-Cap has to offer.




Making a DPDT Switch


You may have noticed that Micro-Cap has a SPST, SPDT, and a DPST. Is there a DPDT? No. It was left out. So what do you do if you need one? Well, it's pretty easy to construct.

First of all let us review what the terms mean. The two terms most relevant are Throw and Pole.

THROWS: This is the number of separate wiring paths, other than open, that the switch can provide for each pole.

POLES: This is the number of electrically separate switches controlled by a single physical actuator.

So for a DPDT we need two poles (switches) and two throws (paths) per switch. How do we do that? Well we start with SPST and double it. Here is the SPST.

The SPST Switch

Next we change its GROUP so that when it changes state another switch with the same GROUP name will do the same. The GROUP attribute can be changed in the Attribute dialog box. Double click on the switch and change the GROUP attribute to Double_Throw (or any name you prefer). The screen should now look like this:

Changing the GROUP Attribute

Click the OK button and then while holding down the CTRL key, click and drag on the switch. This creates a duplicate of the original switch including the GROUP attribute. When two switches use the same GROUP attribute then any action (such as clicking on it) will be duplicated at the other switch. If you add a battery to each switch and some LEDs to easily show the states, the circuit should look like this.

Changing the GROUP Attribute
If you click on either switch, the other switch behaves the same. Essentially this means that the combination of two DPST switches have the same actuator, and as a result the combination of the two makes a DPDT switch.

You can easily make a 3P2T (three pole double throw) switch using this method. It would look like this:

Changing the GROUP Attribute

You can make an n-pole switch but it must be a 1-throw or 2-throw variety. That's because there are only 1-throw and 2-throw animated switch primitives to use. Perhaps in a future version. Hmm.


Download Fall 2015 Circuit Files

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