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I suppose you need a component that has to dissipate low power (i.e. low current flowing through it). There are many digital potentiometers, on the market, that can be varied sending them a digital word (typically SPI). If you need instead a potentiometer controlled by an analog voltage you can use PIC that converts the analog voltage to digital through an ADC and translate it in a SPI command. Other possibility design by yourself using fet as variable resistor.
Voltage-controlled resistor is a BJT or a MOSFET. You can design a circuit that outputs a voltage or current controlled by a control voltage. You can also try a LM317T voltage regulator, also controllable by a voltage. All depends on what voltage range you need at output and what is the load.
There are things called photoresistive opto-couplers. They control a resistance with current through an LED which shines on a photoresistor. The controlling voltage source should drive the LED through a series resistor. Try a net search for "photoresistor optocoupler". It is not a potentiometer exactly. Just a variable resistance without an output tap. Then, clever ways are used to fashion a true potentiometer with this idea. Search for "potentiometer optocoupler". BTW use an image search and not a web search. It shows up lots more ideas. For this application, light is your friend.
Standard optocouplers basically have a current type (high impedance) output. If you want a variable resistance then you could use a photoresistive type coupler as Analog Ground mentioned such as this.
Generally, an optocoupler is not used unless the isolation characteristic is needed. Does changing the RC circuit require the isolation? Is there another way to get the same effect in your application? What is going on when changing the RC circuit?
There is mechanical version of this. You need to use voltage to turn the internal motor. This best suites for the high resistance potentiometer. You may come across some IC type digital controllable potentiometer, but that mostly applied for low power and small value resistance
tell me please exact brand that are popular and run longtime. I buy every month potenionmetors. Someone Suggest me LG potenionmetors does it is comfortable and run long time.
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