Taxi hands-free system, function

Function requirements

 No overvoltage and undervoltage
(is recognized by special vehicle multifunction control unit (SVMCU [MSS]) (N26/9))

The hands-free two-way radio enables the taxi driver to communicate via two-way radio, e.g. with the taxi headquarters.

The hands-free two-way radio consists of the following components:

 Two-way radio (A49)

 (Electret) microphone (B25)

 Left front door dual coil speaker (H4/19)

 Lower control panel control unit (N72) with
two-way radio switch (N72s11)

 Roof antenna (A22/2)

The two-way radio is supplied with power via the SVMCU [MSS].

When the two-way radio switch (N72s11) in the lower control panel control unit (N72) is actuated, the two-way radio (A49) is switched to transmission mode. At the same time, the speaker output of the radio (A2) is muted. Now you can speak via the microphone (B25) located in the overhead control panel.

The radio reception is output via the left front door dual coil speaker (H4/19). This speaker is also used for normal radio operation.



Electret microphone

This microphone does not have a coil and is thus very compact. It is based on the capacitor principle.

A polarized (electret) membrane that serves as a capacitor plate is moved by means of sound. The capacitance in comparison to the parallel, rigid second capacitor plate is thus changed. Electrodes are connected to both capacitor plates. The changing capacitance causes a voltage fluctuation, which can be picked up as a signal and amplified.



If a taxi emergency alarm (code 934) is triggered, the hands-free two-way radio is switched from SVMCU [MSS] to "Listen in".