Does this (combined switch/variable resistor) component exist?

Question

I'm looking for a component like this - similar to a potentiometer, but with a gap in the middle of the resistive element. With the wiper on the far left, red is directly connected to green. As the wiper sweeps clockwise, resistance between green and red increases until they become disconnected. Then red and blue become connected, first with high resistance then decreasing to zero.

Essentially it's a switch combined with variable resistors to allow "gradual" disconnection from green followed by "gradual" connection to blue.

Does a component like this exist? What is it called and how might I find one?

Answer 1

Not as a stock item.

But a common technique is to use a continuous linear pot with a centertap, and ground the centertap. It changes the resistance-to-rotation profile from being two rheostats to two potentiometers, but the grounded centertap does isolate the two halves of the element. Depending on the nature of the signals, the transition could be detectable to give a signal when the wiper crosses over.

Answer 2

From the comments:

Max resistance would need to be about 500 Ω. The component would be in serial with something like a 68 Ω (3 W) resistor, with 12 V across the pair. So (at zero resistance) max current would be about 200 mA, and at 500 Ω resistance current would be about 20 mA.

A thing to realise with potentiometers or rheostats is that the power rating for the whole device is dissipated across the whole track. Take a 1 W, 1000 Ω potentiometer: from \$ P = I^2R \$ we can calculate that the maximum current the track can handle is \$ I = \sqrt\frac P R = \sqrt\frac 1 {1000} = 1 \ \text{mA} \$. Even if you're only using one tenth of the resistance track the maximum current is 1 mA as it's the power dissipation per unit length that will overheat any portion of the resistance track.

In your case you are looking for 200 mA when the wiper is close to either end but it's 1000 Ω end-to-end (ignoring the gap for now). That means the pot would need to be rated for \$ P = I^2R = 0.2^2 \times 1000 = 0.04 \times 1000 = 40 \ \text W \$. That's big and that's hot.

I suggest you edit your post (making it clear where the edit starts so that existing answers don't look stupid) and describe the real problem you are trying to solve.