Audio/Video, Control, and Building Automation Systems
This domain covers systems that control or present information: AV distribution, control systems, and building automation. For AV, understand signal types (HDMI, HDBaseT, DisplayPort, analog) and their distance limits, the need for EDID management and HDCP handling, and audio fundamentals such as impedance matching for 70V distributed speaker systems versus low-impedance 8-ohm systems. Know why 70V constant-voltage distribution allows many speakers on one amplifier and long runs.
For control systems, know the common physical layers and protocols - RS-232, RS-485 (multidrop, termination, bias), IR, IP, and relay/contact closure - and how each is used to control displays, shades, and equipment. Understand that RS-485 needs proper termination and biasing and that ground potential differences cause failures. For building automation, know BACnet and Modbus basics, the role of sensors and actuators, and the concept of a sequence of operations. Understand analog versus digital inputs and outputs, and 4-20 mA and 0-10 V signaling, including why a broken wire on a 4-20 mA loop reads as a fault.
Traps: confusing RS-232 point-to-point with RS-485 multidrop; assuming HDMI works reliably at long distances without extension; mixing 70V and 8-ohm speaker wiring; and forgetting that a control system must fail to a safe state when communication is lost. Also expect questions on commissioning and point-to-point verification.
Worked rule of thumb: for any control interface, define the failure mode first (loss of power, loss of network, loss of sensor), then verify the wiring supports detection of that failure. Commission by testing every point individually before testing sequences.