Which PCB controls and drives the alphanumeric display LEDs, the bar graph LEDs and the alarm indicator LED?

• A. Alarm Interface Board
• B. Display Board / Display Assembly
• C. Power Board
• D. Control Processor Board

Answer: (B)

LED indicators like alphanumeric digits, bar graphs, and an alarm LED need specialized drive circuitry to manage multiplexing, brightness, and timing. The Display Board / Display Assembly serves this role, taking data from the Control Processor Board and turning it into the signals that light each segment or bar at the right moment. It handles the current limiting and multiplexing required to drive multiple types of displays, so the alphanumeric characters can be scanned, the bar graph segments can be lit proportionally, and the alarm indicator can flash or stay on as needed. The Control Processor Board provides the content and the timing logic, but it relies on the display board to physically illuminate the LEDs. The Power Board simply supplies power to the system, and the Alarm Interface Board handles alarm signaling routes rather than driving the displays themselves. Therefore, the Display Board / Display Assembly is the correct choice.