I have a circuit that is controlling a water valve.
The state of the valve can be controlled via an http request, or a physical rocker switch.
I would like the physical rocker switch to represent the current state of the water valve. ie it is in the "Open" or "Closed" position.
This means that if the valve is closed or opened over the http request, then the switch moves to represent that state.
Does such a switch exist?
The best solution is to use a momentary switch to both manually open and close the valve rather than a physical rocker switch - this would require an additional latching circuit to record the switch value and compare it to the current state of the valve and open or close it accordingly. The state of the valve could be displayed by a bi-color LED - red for closed, green for open. Then, the LED would give you the state information (regardless of if the action came from the switch or HTTP request), and the position of the switch would be meaningless since it is only momentary and always "open" unless it is being pressed.
To do what you are suggesting would involve an actuated switch. These do exist, but they are product-specific and typically pretty expensive. A good example is the older style volume knob on some car radios that have steering wheel control - change the volume with the steering wheel buttons and the volume knob on the radio head unit will rotate accordingly. A lot of digital sound mixing boards have a similar feature for recording gain level settings - press a button and all of the levers and knob automatically adjust.
You could do the same with a rocker switch by connecting internal cables from each end of the switch to a servo motor which would pull the the switch on or off from an HTTP request, and then return to a neutral state to allow manual operation. This solution would be overly complicated - hence the reasoning behind LED indicators and a single momentary push button instead.
I would actually suggest a momentary toggle, but with one LED above and one below the switch, to recreate some of the up/down/toggly feel of a toggle. I'd still want them to be different colors though. You could even have multiple colors or blinking to indicate error codes.
Panavision and technicolour would be an illuminated rocker switch with independent LED control. The LEDs display the current state; the switch captures the local request. A microcontroller handles the local and http requests and turns on/off the LEDs. SPDT rockers with independent LED control is a pretty tall order.
I would suggest 2 momentary SPST buttons with independent LED control, and each with a different lens colour.
The simplest device that the microcontroller can use to turn to the valve on or off is a relay. One might think that a relay could be available that would expose a mechanical lever to which displays the state and allow the user to "manually" turn it on or off. However, the manual interaction wouldn't affect the current in the relay's magnet, so even if the manual action forced the relay's switch to the on or off position, that effect would be undone when the lever is released.
There is a device called a "latching relay" which switches based on a pulse of current to either the "turn on" coil or the "turn off" coil, after which it stays in that state. Such a relay could be made to expose a lever which would work as you want. However I don't see any such devices.
I think a reasonable solution would be similar to the other suggestions here: Given that the microcontroller already has the wherewithall to switch a relay, have it read a couple of local pushbuttons too, for manual on and off. (Could even be a center-off momentary rocker, if the rocking aspect is important. The LEDs could even be in the two rocker switch halves.).
I would also suggest that the microcontroller be able to read the actual state of the relay, so it can report that back to the http interface. You can either have it read the power going to the valve, or use a relay with an extra set of contacts.
Another approach is to follow the "NVR switch" safety protocol used in machine tools.
"NVR" stands for "No Volt Release" so that if power is interrupted, the machines stop, and don't restart unexpectedly when power is restored.
One (green) momentary push button switch to start : traditionally, this switches power to a relay coil, and when the relay energises, one of its contacts is used to maintain power to the coil. Normally this also illuminates a light to show the equipment is running.
One (red, highly accessible) switch to stop : pressing this breaks the circuit to the relay coil, disconnecting power.
This is a little more complex than the "momentary switch" approach.
I understand that your question is about the switch and not the water valve, but I am on board with a few others on looking at the vale too. I have used several actuator controlled ball valves for dirty water systems from Spears Link to spec sheet that have several options for control that would lead to a simple indicator circuit. Diaphragm vales such as RainBird's Link to product list have a DC latching solenoid options as well as the normal 24VAC operation.
