Audiovisual Integration and Control
What this domain tests
This domain tests control interfaces and sequences: RS-232, IR, IP, CEC, relays, and GPIO. It also tests how control systems verify state, handle handshakes, and recover from failed commands. Items often involve choosing the most reliable control method or calculating a relay/port load.
Core rules
- RS-232 is point-to-point serial control with parameters such as 9600 baud, 8 data bits, no parity, 1 stop bit; null-modem wiring crosses transmit and receive.
- IR control is one-way and state-blind unless the device provides discrete commands or feedback. IP control can provide two-way status and is preferred when the device supports it.
- CEC is a consumer control bus over HDMI; it is convenient but not reliable for professional multi-device sequencing because of vendor variation.
- Relays and GPIO can trigger screens, lifts, and power control; check coil current and contact ratings.
- Good control design uses discrete commands, explicit feedback, and timeout/retry logic rather than toggle commands.
Worked example
A 24 V relay coil has a resistance of 200 Ω. Find the coil current and decide whether a control port rated at 500 mA can drive it directly.
- I = V / R = 24 / 200 = 0.12 A = 120 mA.
- The port rating is 500 mA, so 120 mA is within the rating, but you must also verify the port is designed for an inductive load and has suppression. Reasoning: the calculation is simple, but the practical answer includes load type and flyback protection, not just current.
Traps
- Using toggle commands when discrete on/off commands are available.
- Assuming CEC will work identically across brands.
- Forgetting null-modem wiring for RS-232 between two DTE devices.
- Driving an inductive relay coil without suppression.
- Omitting feedback and timeout handling, so the control system reports success when the device did not respond.