| 摘要 |
A transmitter (10) and one or more receivers (12) are linked by infra red transmission via LED (14) and photodiode (16). In normal use, in-flight entertainment is modulated on left and right channels to give stereo sound on a user's earphones (28a, 28b). Transmitter public address signal on one channel and a code signal on the other channel. At the receiver (12), the code is detected (at 36) to operate receiver switching means (38) which disable the user's volume controls (30), thus ensuring that the public address message is heard at full volume. Also described are improved infrared signal receiving arrangements mitigating the effects of ambient light interference.
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