Forums » CircuitLab Support Forum

I made an RC time circuit and it worked with one timed switch using time-domain simulation. Connecting a second switch (SW3) also worked but if I disconnected the second switch and leave it unconnected all I get is the gray simulation box. No simulation.

Maybe it's just confused by an unconnected part, I don't know.

Great program so far. Fun to play with.

Unconnected components are inherently a problem for the simulator. How can the simulator possibly solve for the voltages on the unconnected component? All nodes of SW3 will be the same voltage (since no currents flow through the switch), but no equation can be written that would allow for solving the voltage on that component.

In the real world, if you tried to measure the voltage, your voltmeter would, during the measurement, provide a DC connection to the switch; a floating (e.g. battery powered) voltmeter would read zero volts from the switch to any other node you measured to. (Each reading would imply a different result, all of which would be correct, hence the simulator's problem).

You need to do connect the floating component to get it to simulate. Even an unreasonably high resistor (a million Megohms) from any terminal of the switch to any node would allow the simulator to solve for the voltage. The switch would then sit at the voltage of the node you tied it to.