If you need a potentiometer with a power switch, but you only have a dual gang potentiometer without a switch, then what could you do?
Step 1: Open the Potentiometer Back Cover
Step 2: Remove the Potentiometer Back Cover
Leave the top portion, shaft and the bottom slider in place.
Step 3: Cut the Carbon Track
By cutting the carbon track, the voltage on the track no longer follows the original taper of the potentiometer. When the potentiometer slider crosses the gap, the voltage chances suddenly.
It might be a good idea to make the cut V- shaped, otherwise the slider slowly smears the carbon on the surface.
You have just created a slide switch! (The track still has its original resistance, but that does not matter after you add a MOSFET.)
Now replace the pcb, bend those notches back and mark the terminals. NO is normally open, C is common and NC is normally closed.
The circuit depends on your application. The pulldown resistor should be about ten times higher than the potentiometer resistance. For low current devices you can substitute the mosfet with a bipolar transistor (you need a base resistor then.) You can also use the switch with a microcontroller input, but there might be noise since this is not a really high quality switch. The hack works with linear and logarithmic potentiometers. Log potentiometer would be great for a PWM light dimmer circuit, maybe with a 555 IC.