Psion Teklogix OMNii HDK XT10, Руководство пользователя

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Chapter 6: Omnii Expansion Ports and Connectors
Audio Reference Designs
88 Psion Teklogix Omnii HDK User Manual
6.3.1.2 Push-to-Talk Handset
The push-to-talk handset reference design uses a 3.5 mm audio jack to accept a variety of push-to-
talk handsets with a differentially driven loudspeaker. These handsets have a switch which
enables/disables the microphone in the handset allowing audio to be played through the handset
while the microphone is disabled. To speak, the user pushes the switch enabling the microphone.
Audio output is driven from a class D amplifier on the main logic board which provides sufficient
power to drive the loudspeaker.
Similar to the single-ended headset audio expansion board, filtering capacitors are placed at
various locations throughout the audio paths to prevent GSM interference from coupling in. As
well, the microphone biasing and signal conversion is performed identically to the single-ended
headset reference design.
If a push-to-talk radio with a different activation scheme is used, a different detection circuit will
need to be designed.
Figure 6.7 Block Diagram of the Push-to-Talk Handset Expansion Board
3.5 mm Audio Jack
The reference design for a push-to-talk audio expansion board has a 3.5 mm audio jack which
provides connections to a single-ended microphone and a differentially driven loudspeaker. This is
the only connector configuration supported in the reference design.