METHOD OF RETROFITTING A DATA COMMUNICATION SYSTEM TO A VEHICLE

Abstract

A method and apparatus are disclosed for enabling an existing wire supplying DC current to an electrical load of a vehicle to serve as a clean line for transmission of a data signal without interference from electrical systems of the vehicle. The method comprises identifying opposite ends of the existing wire, cutting the wire at the opposite ends and inserting a respective inductor in series with the wire at each of the opposite ends, to define an intermediate wire section that extends between the two inductors, and coupling data transmitting and receiving units to the intermediate section of the wire to permit data transfer between the transmitting and receiving units.

Claims

1. A method of enabling an existing wire supplying DC current to an electrical load of a vehicle to serve as a clean line for transmission of a data signal without interference from electrical systems of the vehicle, which method comprises identifying opposite ends of the existing wire, cutting the wire at the opposite ends and inserting a respective inductor in series with the wire at each of the opposite ends, to define an intermediate wire section that extends between the two inductors, and coupling data transmitting and receiving units to the intermediate section of the wire to permit data transfer between the transmitting and receiving units.

2. The method as claimed in claim 1, wherein each of the transmitting and receiving units derives dc power from the existing wire.

3. The method as claimed in claim 2, wherein the transmitting and receiving units are only operational at times when power is delivered by existing wire to the electrical load.

4. The method as claimed in claim 2, wherein the intermediate section of the wire is connected to receive DC power even when no DC current is to be supplied to the vehicle load and the transmitting and receiving units serve additionally to control a switching device for activating the vehicle load.

5. The method as claimed in claim 1, wherein the transmitting unit is connected to receive a composite video analogue signal from a camera and to modulate the analogue signal onto the carrier and the receiving unit is connected to a monitor in order to display the image captured by the camera.

6. A communication unit for connection within a break in a wire connecting a DC power source to an electrical load of a vehicle, which wire forms part of vehicle wiring that is subject to high frequency interference, the unit comprising a first connection terminal for connection to a first side of the break in the wire, a second connection terminal for connecting to the other side of the break in the wire, an inductor connected to the first and second connection terminals to reestablish electrical continuity of the wire and thereby permit flow of DC current to the load while preventing high frequency interference from passing between the two connection terminals, and a modem serving connected to one of the terminals to enable data communication with a second communication unit via a section of the wire that is isolated from remaining wiring of the vehicle by the inductor.

7. The communication unit as claimed in claim 7, further comprising a voltage regulator that is connected to one of the first and second connection terminals and serves to provide a stable DC voltage for powering the modem.

8. The communication system as claimed in claim 6, wherein the inductor has a current rating in excess of 6A and an inductance value greater than 50 μH.

9. The communication system as claimed in claim 8, wherein the inductor has an inductance value greater than 100 μH.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

[0018] FIG. 1 shows a conventional circuit for powering a reversing light,

[0019] FIG. 2 shows the manner in which a video system may be installed in a vehicle using only the existing wiring shown in FIG. 1,

[0020] FIG. 3 is a detailed circuit diagram of the transmitting unit Tx in FIG. 2,

[0021] FIG. 4 is a detailed circuit diagram of the receiving unit Rx in FIG. 2, and,

[0022] FIG. 5 is a diagram similar to that of FIG. 2 showing the installation of a video system in a circuit where the load need not be powered at the time that the video system is in operation.

DETAILED DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 shows wiring already present in any vehicle fitted with a re versing light. The vehicle battery 10, which is a 12V battery in most cars and vans but may be a 24V battery in larger commercial vehicles, is connected to a switch 12 associated with the gear selector. When reverse gear is selected, the switch 12 is closed and to send power over a wire 14 to the reversing light 16. The light 16 is shown in FIG. 1 as being an LED but it may alternatively be a filament bulb. In the case of an articulated vehicle, part of the wire 14 will be in the tractor and another part in the trailer, the wire 14 being included in an electrical connector for connecting the wiring of the trailer to the tractor.

[0024] FIG. 2 shows how the existing wire 14 can be used to allow installation of a video system. The video system comprises a display screen 18 or monitor mounted in the cab to be visible to the vehicle driver and a camera 20 mounted at rear of the vehicle or the trailer.

[0025] A transmitting unit Tx, described in more detail below, is used to connect the camera 20 to the wire 14 at the rear of the vehicle, while a receiving unit Rx connects the display screen 18 to the front end of the wire.

[0026] In known systems, the transmitting and receiving units are coupled to the wire 14 by way of DC decoupling capacitors and the wire is not interrupted so that the DC supply path to the load remains undisturbed. By contrast, in the present invention, the wire 14 is cut and each of the transmitting and receiving units has two connection terminals, labelled Power In and Power Out, for connecting it in series with the wire 14. After the wire 14 is cut, each side of the cut is connected to a respective one of the two connection terminals.

[0027] In this way, the wire 14 is separated into three different sections, designated 14a, 14b and 14c. The connection of the intermediate section 14b to the sections 14a and 14c is by way of inductors, or chokes built, into the transmitting units Tx and Rx, each of the chokes being connected across the two connection terminals of its unit. The chokes will be described in more detail below with reference to FIGS. 3 and 4.

[0028] Each of the chokes allows a DC connection between the connection terminals of its unit but prevents high frequency signals from passing from one of the connection terminals to the other. As a result, while the sections 14a and 14c are connected to the remainder of the vehicle wiring and may carry interference signals, the section 14b, which is highlighted in the drawings, cannot receive interference signals and is sufficiently clean to carry a video signal from the camera 20 to the display screen 18 without significant signal degradation. All three sections 14a, 14b and 14c however remain at the same DC potential and allow DC power to be transmitted to the reversing light 16.

[0029] The construction of the transmitting unit will now be described with reference to FIG. 3. The Power In and Power Out connection terminal of FIG. 2 are shown in the top right corner or FIG. 3 and the inductor connected across the two connection terminals is designated L103. A first function of the transmission unit Tx is to pass DC voltage from connection terminal Power In to the connection terminal Power Out to supply DC current the reversing light and this take place through inductor L103.

[0030] A second function of the transmitting unit Tx is to send an amplitude modulated video signal to the receiving unit via the connection terminal Power In. This signal is generated in the modem block 110 shown at the bottom left side of FIG. 3. The modem block 110 receives a signal from the video camera 20 via the terminal designated Video In, which is applied via a capacitor C107 to an integrated circuit U101.

[0031] The integrated circuit (IC) U101 is a video modulator/demodulator LA727910V that is commercially available from ON Semiconductor and is used in door intercom systems. The IC U101 produces on an output pin connected in FIG. 3 to a capacitor C102 an analog signal of predetermined carrier frequency that is amplitude modulated in accordance with the image viewed by the camera and applies it to the connection terminal Power In leading to the receiving unit RX. The resistors R101 and R104 and the capacitors C101, C103, C104, C105 and C106 are as specified by the manufacturer of IC U101 to establish the required voltages and impedances at the various pins of the integrated circuit. The diode D101 is a transient voltage suppressor, provided to safeguard against spurious voltage spikes.

[0032] It should be clear to the person skilled in the art that alternative modulator/demodulator IC's may be used in the modem block 110 and that the surrounding circuitry will be dependent on the selected IC.

[0033] All the remaining circuitry in FIG. 3 serves mainly to provide the DC power required by the modem block 110. The IC component U103 of the block designated 114 is a buck, or step down, regulator that is required in a vehicle with a 24V battery to provide stable 12V. Together with resistors R103, R105 and R106, inductors L101 and 102, diodes D102 and D104 and capacitor C110, C11, C112 and C113 a stable 12V supply is developed across the capacitor C114.

[0034] The block 112 has two 12V output supply terminals. The one at the top left hand side of the drawing provides power to the modem block 110 while the second supplies the camera and is further smoothed by diode D103, inductor L104 and capacitors C115 and C116. An LED D105 connected across the capacitor C115 by resistors R102 and R108 serves only to indicate that power is available to the camera 20 and the modem block 110.

[0035] The modem block 110 requires a supply voltage not of 12V but of 5V. The block 116 shown at the bottom right of FIG. 3 receives 12V and uses a regulator IC U102 and two capacitors C108 and C109 to provide the 5V supply VDD that is applied to the modem block 110.

[0036] The receiving unit Rx of FIG. 2 is shown in FIG. 4. Here, the Power In and Power Out terminal connectors are shown at the top left side of the drawing and are connected to one another by an inductor L201. The components within the block 210 act as a demodulator. The IC U202 may be the same as the IC U201 of the transmitting unit, albeit configured differently.

[0037] The Power Out connection terminal, which receives an amplitude modulated carrier frequency from the transmitting unit Tx applies the RF component of the incoming signal to a terminal of the IC U202 by way of capacitor C205. This results in the IC U202 producing a video output signal that is transmitted to the display unit via the capacitor C201. The remaining components within the demodulator block 210 are specified by the manufactured of the IC U202 and will depend on the choice of IC. In FIG. 4, these components are resistors R204 and R207 and capacitor C206, C207, C210, C211 and C212. A second Video Out terminal is connected to a virtual ground VSS via a capacitor C203.

[0038] The block 212 in the top right hand side of the drawing is a voltage regulator using a linear voltage regulating IC U203, capacitors C208, C214, C213, C209 and C204. The voltage regulator is connected to receive the DC component of the voltage on the connection terminal Power Out by way of a diode D204 and a resistor R201. A transient voltage suppressor D203 is provided to protect the circuitry of the receiving unit Rx from voltage spikes on the Power In terminal.

[0039] The remaining circuity is to provide an indication via an LED D201 that there is power and that there is a received video signal. The IC U201 is a dual Schmitt-trigger inverter that powers the LED D201 to flash when power is present and to remain on constantly when a modulated carrier signal is received from the transmitter unit Tx. The IC U201 has different pins connected to the IC 202 and to the VDD power line, its remaining pins being connected to resistors R203, R205 and R206, capacitors C202 and C215, diode D202 and to the LED D201 by way of resistor R202.

[0040] In FIG. 2, it is assumed that DC power is always supplied to the drive load (the reversing light 16) when the video system is to be operated. This however is not essential and in FIG. 5 the video system may operate when no power is supplied to the driven load.

[0041] The embodiment of FIG. 5 differs from that of FIG. 2 in that a switch 512a for operating the load is not connected in series with the load but to a modified receiver unit Rx′. The modified receiver unit Rx′ can now transmit a signal encoded onto a carrier to a modified transmitting unit Tx′ which on receipt of the encoded signal activates an electronic switch or relay 512b to apply power to the driven load 16. The video system can in this case be operated at all times and power sent to the drive load on demand.

[0042] While the invention has been described above by reference to transmission of a video signal over existing vehicle wiring, it may be used for other data signals that require a clean line to avoid the data from being corrupted by interference from other systems installed in the vehicle, such as ignition or fuel injection systems.