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2.8 Electrical Realisation of Interfaces

The diagram below shows the basic arrangement of the two interface techniques:


Figure 2 Basic arrangement of interfaces

2.8.1 Detailed description

Example 1

This data interface uses bipolar signalling; that is, the circuit switches between a positive and a negative voltage. This kind of interface has a good immunity of signal distortion. It allows data transfer in both directions and is directly readable by the MoBIC processing unit.

The voltage ranges for this EIA-232-D/V.24 are shown in Fig 3. Most signals higher than +3V and lower than -3V will function with the circuit successfully. Nine pins of a 25 way connector are used (Pin 1 through 8 and 20). The Electronic Industries Association (EIA) and CCITT define serial ports as interchange circuits at the interface between the data terminal equipment (DTE) and the data circuit-terminating equipment (DCE) for the transfer of binary data, control and timing signals. In this example MoBIC would be the DCE and the Obstacle-Detector the DTE.

Illustration of valid voltage regions:


Figure 3 Valid voltage regions

Electrical Limits:

(see CCITT recommendation V.28 for detailed electrical parameters)

Data Interface Connections:


PIN                  V24 No.              NAME                Abbr.         

1                    -                    shield              PG            

2                    103                  Transmitted Data    TxD           

3                    104                  Received Data       RxD           

4                    105                  Request to Send     RTS           

5                    106                  Clear to Send       CTS           

6                    107                  Data Set Ready      DSR           

7                    108                  Signal Ground       SG            

8                    109                  Data Carrier        DCD           
                                          Detect                            

20                   108/2                Data Terminal       DTR           
                                          Ready                             



(see CCITT recommendation V.24 and ISO 2210 for detailed information)

Mechanical interface:

The connector is realised as a D-SUB 25 female-connector (DB25S).

(see CCITT recommendation V.24 and ISO 2210 for detailed information)

Example 2

This example is by far the simplest way to integrate an audio source into the MoBIC system. For example this audio source could be a 'talking sign', a beacon which identifies itself via an infrared data-link. The talking-sign is a kind of additional sensor for a MoBIC system (in underground-station, buildings, ...). Bi-directional data-transfer is not possible. The audio output from the 'talking-sign'-receiver is taken as an audio-input for the MoBIC audio mixer and then transferred to a headset, for example. The activities from the MoBIC processing unit in this example are strongly restricted. It is only possible to switch the external device's input on or off (see Fig. 2).

Electrical Limits:

PIN description:


PIN         NAME             Abbr.     

1           Ground           GD        

2           Signal           SIG       



Mechanical interface:

The connector is realised as female-CHINCH connector. It is also called phono or RCA plug. It is a small shielded coaxial plug.

Shield : GD

Centre: SIG


Figure 4 RCA plug


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