I'm working on a custom piece of hardware where a fan is turned on and off automatically. The user can override the decision of the automatic system through a switch. Activating the switch when the fan is on will turn it off, and vice versa.
Is it a valid choice to use a toggle switch (see the image below) for that, if the switch is positioned horizontally (i.e. the handle facing either left or right)? Or should I use a button switch instead?
Those switches, when put vertically, are usually associated with on/off actions, where the handle pointing upwards means something is turned on, and when it points towards the floor, it means the thing controlled by the switch is off—although, in some countries, the opposite may be true. In my case, however, the actual position of the handle doesn't mean anything about the current state of the thing under control; instead, the switch acts only as a way to change the state.
As the question attracted much more attention that I was expecting, here are a few details about the aspects which were originally unclear. I add them here instead of editing the question itself in order to avoid invalidating some of the answers.
While the user can override the decision of the automatic system, such override is limited in time. There are two goals for that. The first one (which should be quite common) is to prevent someone from turning the fan off, and forgetting to turn it back on. Or force it to stay on for a long time, when it may not necessarily be needed. The second one (which should happen rarely) is for the automated system to take the control of the fan back in a situation where appropriate. For instance, if the user decided that he wants a quiet environment, but one minute later the system starts overheating, starting the fan would be an appropriate response from the automated system (the other would be to cut the power to the whole system—this is definitively not something the user would enjoy).
This makes it impossible to use on/auto/off switches, unless they have some sort of a reset feature where the automated system itself can toggle the switch back to “auto” position. A possible option would be to use two push buttons, “on” and “off,” and three LEDs indicating the state of the system, only one LED being on at a time.
The design of this part of the system should not take in account the users who want to actively harm/hack it (by manipulating it to permanently switch the fan off, for instance). In fact, if the system is brought into a risky state, it would cut the power to itself. Turning it back on would require a manual action of a technician.
Right now, the three solutions are:
An off/auto/on switch which can reset itself to “auto.” Don't know if such a thing exists.
A series of two buttons: “off” and “on,” with three LEDs: “off,” “auto,” and “on.” The active LED shows the state. The user can press a button to activate another state.
A single push button, which changes the state (the currently accepted answer), and possibly a RGB LED showing the current state (although the fan is loud enough by itself). I'll start by testing this one, as being simpler, and would revert to the previous one if the single button approach would seem not intuitive enough.
