Digital bargraph display driver circuit
simulate this circuit &ndash; Schematic created using CircuitLab

If your microcontroller can output PWM, then set it to a high PWM frequency, and use a low-pass filter to generate a voltage. Something as simple as a resistor from PWM output to a capacitor, and a resistor across the capacitor to ground, as well as signal into the bar graph input, will probably work well (enough).

Try a 10k resistor in, and a 1 uF capacitor, and a 10k resistor in parallel with the capacitor. This is assuming that the bargraph has a high impedance input. If there is a significant load in the bargraph input, R2 is not needed.

The duty cycle of the PWM output will determine the voltage that gets sent to the bar graph. Just make sure the uC output voltage range is compatible with the bargraph input; else re-buffer with an opamp or source follower or whatever.

If I had this problem, though, I'd simply use 10 digital output pins of the uC to drive 10 LEDs arranged in a bar directly :-)