Control of attenuators used to regulate optical signals is disclosed. An assembly including an IR source and an IR sensor is provided to sense blockage of optical signals transmitted between two collimators via a fixed common light blocker that is driven by a motor. The motor is controlled to make sure that that the reset of the light blocker is properly done in an event in which a power supply is intentionally or incidentally cut off. An auxiliary power supply is provided to energize other parts in an attenuator should power supply is intentionally or incidentally cut off.