A contact image sensor can illuminate a portion of a banknote with one or more light emitting diodes (LEDs), capture an image of the portion of the banknote with illumination reflected from or transmitted through the banknote, and generate a digital output signal that represents the captured image. A controller board can receive the digital output signal, generate one or more LED control signals, each LED control signal including changes in voltage to indicate times to switch a light emitting diode on or off, direct the one or more LED control signals to the contact image sensor, bypass digital LED control circuitry that is included with the contact image sensor, and switch the one or more LEDs in the contact image sensor on or off at the times indicated by the respective light emitting diode control signals.