Motorized potentiometers are easy to find and often used e.g. in music studio equipment, but I could need a similarly motorized rotary switch for a project. I am either searching for the wrong term (are such switches known under a specific name?) or they are very hard to find. The rotary switch will be used as an input device to a micro controller, but I need the micro controller to be able under specific circumstances to kind of 'override' the user input and choose one of the other selections. The microcontroller can of course simply ignore the user input and do whatever it likes, but it would make operating the device much easies and intuitive, if the micro controller was able to actually move the switch, so that the knob position could also be used as a visual feedback to the operator.
The switch should ideally have a 15° turn between each position. I will likely only need 7 positions, but due to panel design, these should be in reach within a ¼ rotation or so. As long as I somehow can drive the motor from a micro controller, the type of control interface is of less importance. If it is necessary, I could also drive a 4-wire stepper motor directly.
I do not have any specific requirements for the switch regarding voltage, current or behaviour (bouncing, break before make etc). It should only provide control signals to the micro controller and any behaviour sanitation can be made in software.
The only ready-to-use product I have found is from the Swiss company Elma. They have several different rotary switches which are compatible with a motor driver they call 'Remote Audio Plus'. The motor driver comes complete with a micro controller, IR receiver and can be operated with a standard IR remote control, as it is primarily targeted for use in audio amplifiers. I don't need the remote control functionality, but the controller also has an input interface and can be controlled independent of the IR receiver using a simple protocol. This product would cover all my requirements, but it is not exactly cheap. The motor drive alone retails at around €350 and that is not just slightly outside my budget.
I realize that I with some effort probably could adapt any stepper motor to operate a rotary switch, but I don't have the tools or knowledge to make the necessary fittings, brackets or whatever is needed to combine a motor and a switch, so a ready-to-use product will very much be preferred.
Do anyone of you know of a product, which at least comes close to my requirements?
Answers to comments:
Are alternatives viable? If not a must-have, this is at least a want-very-much. I have tried to consider other options as well, but not found anything making sense. The motorized switch is indeed not crucial for the thing to work, but there will be several rotary switches and potentiometers on the same panel and only one of the switches and one of the potentiometers should be motorized/automated. If I replace just the switch with e.g. a rotary encoder and display combination (or some other type of input and feedback mechanism), I ought to do that with all the other inputs as well for consistency and that would compicate things a lot and also IMHO mess up the visual design. Having knobs with a notch indicating the position would be preferrable, because all switches and potentiometers then would look the same.
Have I considered to have anything custom made? Not really. I can't believe that a custom made device is any cheaper than the Elma system I already mentioned and the price is the reason why I am searching for alternatives.
Best Answer
Consider using a motorised rotary pot, connected to an ADC read by the MCU that controls it, which also controls solid state analog switches (or relays as appropriate). (If it's merely input to a micro, these switches are unnecessary; I mention them in case you need real switching too)
You won't get the click detent of a rotary switch, but you can simulate that by driving the motor.
As you turn it, the ADC reading increases : when it crosses 50 increasing, drive the motor (at low torque = low current) to 100. If the user lets go at 125 it springs back to 100; if at 175 it clicks forward to 200. Experiment with torque and deadbands (90 to 110 count as 100) to get the feel you want without motors chattering.
Number of switch positions is obviously software configurable.