In a microcontroller interfacing with an analog sensor using a simple ADC and PWM, what is the role of PWM?

• A. It is used as a digital-to-analogue approximation via a smoothing RC filter
• B. It directly measures analog voltage
• C. It converts digital values to digital codes
• D. It amplifies the signal

Answer: (A)

PWM's role here is to provide a controllable analogue-level output by converting a digital duty cycle into an average voltage. The microcontroller's PWM output switches between 0 and a supply voltage at a high frequency. When you pass that switching signal through a smoothing low-pass filter (like an RC network), the high-frequency components are attenuated and the remaining signal is a steady DC level whose value is proportional to the duty cycle. That smooth voltage can then be read by the ADC to obtain a corresponding sensor or control value. This is effectively using PWM as a crude DAC.

It’s not measuring anything, so it doesn’t make sense to say it directly measures analog voltage. It also isn’t converting digital values to digital codes—that’s the ADC’s job, and the PWM isn’t an amplifier, so it doesn’t boost signal magnitude; it merely modulates the average level through switching.