Analog 3-state buffer where the input voltage equals the output voltage and is controlled by a digital control line

Question

I'm looking for a device that can control an analog signal without interference. I need it to be controlled by a digital control line (0v - 5v). The input voltage (0v - 5v) should equal the output voltage (0v - 5v). It doesn't matter if the control line is active high or active low. If the control line is active then the output should equal 0v.

An example application might be as shown below. You have a blinking LED but you also want to control the brightness of the LED using a pot.

^{simulate this circuit – Schematic created using CircuitLab}

Answer 1

For what you have an N-channel MOSFET will do what your need if configured as shown below.

^{simulate this circuit – Schematic created using CircuitLab}

However, you may find the circuit below works better.

It uses a simple current regulator circuit with a logarithmic pot you can use to adjust the current from about 1ma to close to 20mA and hence the brightness of the LED more linearly. (Assuming it is in the right way round :)

The clock line enables the current regulator.

^{simulate this circuit}

Answer 2

Why not just drive a 5V square wave to the pot?

However your LED circuit likely wont do what you expect - LED brightness is not linear with current (or voltage) - the best way to dim a flashing led is by gating a PWM signal on and off