GB2215564A - Data communications - Google Patents

Abstract

A connector device has one part (2) which defines a circular, smooth-walled recess into which a plug projection (22) of another connector part (4) fits. The recess and plug projection have plane mating surfaces (8, 24) behind which are mounted receiver and transmitter induction coils (14, 16). When the parts are mated the transmitter coil of one part is aligned with the receiver coil of the other part to form two serial data links. Each connector part also includes a transmitter circuit and a receiver circuit connected to the respective coils. The transmitter circuit converts one of two input logic levels into a series of oscillations at a frequency substantially greater than the maximum data transmission frequency, and the receiver circuit converts such a received oscillation sequence into a steady logic level. <IMAGE>

Description

DATA COMMUNICATIONS The present invention relates to data communications and, more specifically, to a connector which allows data to be communicated between two separate machines.

In computer based systems it is generally required to connect two or more computers or peripheral machines together by means of a cable incorporating data carrying lines either for serial or parallel transmission of data. Such a cable requires a connector at each end.

Generally such connections are provided by plug and socket devices, where one part of the connector has a series of exposed pins and the other part defines a corresponding array of sockets which receive the pins.

Such connectors are widely used in connecting computers to peripheral devies such as printers or modems and for networking computers and peripheral devices together.

However, for some applications where the connector device is intended to be disconnected and reconnected many times, such plug and socket devices are unsuitable. Where multi-pin connectors are used, the pins may become bent. Moreover, where one part of the connector is left exposed on a piece of equipment, it is vulnerable to vandalism or damage by the ingress of dirt. It is also possible that excessive voltages may be applied which could cause damage to the associated electric circuits. These problems arise particularly where the connector is intended to be provided on a piece of equipment, such as a banking or security system, a vending machine, or a postal franking machine, where a computer system within the machine stores data which may require to be changed or transmitted to an external device.For this purpose a connector is needed in order to allow another device to be connected to transmit or receive data. For example maintenance staff may require to collect data from vending machines concerning sales made and transmit data to the memory of the machine in order to vary price information. One part of any connector used for this purpose must be permanently provided on the machine and if this consists of a part of a conventional multi-pin plug and socket connector, it is clear that there is a considerable technical problem in ensuring that this part is not damaged by adverse weather conditions if the machine is outside, or vandalism between maintenance visits.

Optical connectors may be used and overcome part of the problem but, nevertheless, exposed optical connector parts are vulnerable to physical damage such as paint spraying and scratching.

It would be possible to provide the connector behind a lockable door as is usual for example in vending machines, but this creates other problems as access to any coin box in the machine is then provided and this may not be desirable when the only operation required is a simple data transfer. It is therefore desirable to be able to have the connector accessible externally of the outer housing of the machine without the need to open doors or slots or enter any key protected area.

The connector device of the present invention is intended to overcome such technical problems. The device of the present invention comprises a connector having two parts which mate together with facing plane surfaces of non-magnetic material, each part comprising a transmitter circuit having an input for receiving serial digital data to be transmitted and an output connected to a transmission induction coil mounted behind said plane surface, and a receiver circuit having a receiver induction coil mounted behind said plane surface and connected to a receiver circuit which has an output for received digital data, the transmission coil of one part being aligned with the receiver coil of the other part when the parts are mated.

Because the interconnection between the connector parts is provided by magnetic induction, the mating surfaces can be completely smooth. They can, for example, be made of mechanically strong fibre reinforced plastics resin, for example TUFNOL (Trade Mark), toughened glass or ceramic material.

In one embodiment the plane surface of one part is provided in the base of a recess and the plane surface of the other part is provided as the end surface of a plug which fits into the recess. The other part may be provided with an O-ring seal around a side wall of the plug which engages with a plane side wall of the recess in order to provide a seal between the parts and hold them in tight engagement in the correct orientation.

The receiver and transmitter circuits are preferably such that they can be used without modification for varying transmission rates either with data transmitted at RS232 compatible levels up to 65K band or for data at normal TTL levels when rates of up to 100 k}3z can be achieved. The function of the transmitter circuit is to produce an oscillating signal in the transmitter coil when and only when the data input represents one only of the two possible logic levels. The connector has no intelligence of its own and requires no special protocol for its operation.

Because of the enclosed nature of each connector part it is even possible to use the connector under water.

An embodiment of the connector will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a perspective view partially cut away of the two parts of the connector; Figure 2 is a block diagram of one embodiment of a transmitter circuit for use in the connector; and Figure 3 is a block diagram of one embodiment of a receiver circuit for use in the connector.

The connector shown in Figure 1 comprises a socket connector part 2, which would normally be fixed into the housing of a machine, and a plug connector part 4 which is connected to a cable 6 which is in turn connectable to another data collecting or transmitting device.

The socket part 2 defines a circular recess with, at its base, a mating plane surface 8 of a non-magnetic material which allows a magnetic field to pass through it. A side wall 10 of the recess is preferably smooth and terminates in a flange 12 which can be mounted flush with the surface of the machine housing. Such a socket is intended to present minimal opportunities for vandal damage. A dummy plug which fits into the socket may be provided, if required, to prevent dirt accumulating in the recess. Behind the mating surface 8, two inductor coils are mounted but only one, 14 is shown in Figure 1. The inductor coil 14 is connected to a data receiver circuit, as shown in Figure 3, the output of which is connected to a serial data output line in a cable 18.The transmitter coil (not shown) is connected to a transmitter circuit as shown in Figure 2 which is supplied by a serial data input line in the cable 18.

The cable 18 also includes a power supply line.

The receiver and transmitter circuits are carried by a printed circuit board 20 mounted behind the mating surface 8 in a housing cavity defined by an extension of the side wall 10. The components of the receiver and transmitter circuits may primarily be mounted on one side of the printed circuit board with the transmitter and receiver coils on the other side. The entire socket connector part may be made extremely compact so that it takes up very little space in the machine to which it is fitted. The diameter of the circular recess may typically be 3 cms though smaller sizes are possible.

An alignment mark is provided on the flange of the recess or on the side wall in order to indicate the orientation of the receiver and transmitter coils behind the mating surface 8.

The plug connector part 4 defines a housing, one part of which is a circular projection 22 which is sized so that it can be received in the recess of the socket part 2.

The front wall 24 of this circular projection defines the plane mating surface of this plug part. This mating surface is, like the mating surface of the connector part 2, made of a non-magnetic material, such as fibre reinforced plastics, toughened glass or ceramic material. Behind the mating surface 24 a printed circuit board 26 is provided on which there are mounted inductor coils and transmitter and receiver circuits identical to those provided on the printed circuit board 20 in the other connector part. The data input and output lines of the cable 6 are connected to the transmitter and receiver circuits respectively.

An annular groove 28 is provided in a side wa].l of the projection 22 in order to receive an O-ring seal 30.

This O-ring 34 provides sufficient friction to maintain the plug and socket connector parts in a fixed orientation when they are mated together. An alignment mark (not shown) is provided on part of the housing of the plug part 4 so that the parts can be mated in the correct orientation. If the alignment mark on the socket is provided adjacent the receiver coil, then the alignment mark on the plug will be provided adjacent the transmitter coil so that when the connector parts are mated, two data circuits are formed in each of which a transmitter coil and a receiver coil are coupled by magnetic induction. Slight misalignment of the coils will not seriously impair the data circuits formed across the connector.

Although the connector has been described as having a circular recess and plug, it will be appreciated that the recess and projection may by of any cross-sectional shape, for example polygonal. Although a polygonal shape may facilitate alignment, the presence of corners in the recess may offer opportunities for damage by vandals and, therefore, the smooth side wall of a circular recess is preferred.

As indicated, the mating surfaces 8 and 24 must be made of a non-magnetic material but the remainder of the housings of both connector parts is preferably made of stainless steel. In both parts a back plate 32, 34 is provided as separate from the extended side wall of the housing in order to allow access to the printed circuit boards 20 and 26. The back plate is connected to the side wall by screws 36.- The cables 6, 18 may project through the centre of the back plate 32 as shown for connector part 2 or through a recess defined between the back plate 34 and the side wall as for part 4.

The receiver and transmitter circuits provided in both connector parts will now be described with reference to Figures 2 and 3. These circuits are practical circuit designs and it will be appreciated that the required functions may be produced by different circuit designs using alternative components.

The function of the transmitter circuit shown in Figure 2 is to convert a logic "1" level at the input 40 into an oscillating signal in the transmitter coil 16. Then the logic level at input 40 represents "0" no oscillating signal should be generated. It would, of course, be possible to reverse this arrangement. In order that the connector may function with various data input rates and with RS232 voltage levels of plus and minus 12 volts, the input 40 is first connected to a level translator 42 for conversion of the input logic levels to normal TTL levels. Since the IC (MAX 232C) proposed for this level translator function is an inverting device, the output is connected to another inverter 44. The output of the inverter 44 therefore represents the same logic level as the input 40.Where the connector is intended to receive data already at TTL levels the level translator 42 and inverter 44 may be replaced by lower cost standard TTL inverters to act as a buffer between the rest of the transmitter circuit and the device to which it is connected in order to prevent interference with the operation of the connected device which might occur if signals from the transmitter circuit were allowed to be transmitted back towards the device.

The output of the inverter 44 is fed to a square wave oscillator circuit operating at a frequency of 2.5 MHz.

This circuit is made up of the components 46, 48, 50, 52 and 54 which are, respectively, a 150 pf capacitor, a diode, a 1K resistor, a 3K3 resistor and a Schmitt trigger. The oscillator circuit may operate at any frequency provided it is at least ten times the maximum baud rate of the input data so as to ensure that a sufficient number of oscillations are produced while the logic level is maintained high in order to provide for proper coupling across the magnetic induction circuit provided by the coupled coils 14, 16. The diode 4Q controls the operation of the oscillator circuit so that it is off while the output of inverter 44, and therefore the input at 40 is at a logic "0" level.While the output of inverter 44 and the input at line 40 are at a logic "1" level, the oscillator circuit is on. The purpose of the resistor 50 is to ensure that the voltage on capacitor 46 does not drop completely during the off period of the oscillator but sits at the bottom threshold voltage of the Schmitt trigger 54. In this way the period of the first oscillation after turning on the circuit is the same as the period of the remaining oscillations. The period of each oscillation is determined by the values of capacitor 46 and resistor 52.

The output of the oscillator circuit is fed to a drive buffer 58 which, in the present example is the five gates of a 74HC04 inverting hex buffer connected together in parallel. The output of this drive buffer is connected so as to energise and de-energise a tuned circuit made up of the transmitter inductor coil 16, a resistor 60 and a capacitor 62 which are connected together in parallel and in series with the coil 16.

This circuit is designed to resonate at the same frequency as the oscillator circuit 46, 48, 50, 52, 54, that is 2.5 MHz in the present example. The purpose of the resistor 60 is to reduce the amount of ringing in the tuned circuit when the oscillator is switched off by the input of a logic "0" level at 40. The waveform across the inductor 16 therefore represents the incoming data signal with a sequence of oscillations representing each logic "1" level of the input data.

The coil 16 is formed by ten turns of 34SWG wire around a nine millimetre diameter pot core. Clearly the size of the coil represents a limiting parameter on the overall size of the connector part. The coil 16 is inductively coupled through the mating surfaces of the connector part to an aligned receiver coil 14 in the other connector part.

The receiver circuit will now be described with reference to Figure 3. The receiver coil 14 is identical to the transmitter coil.

One end of the coil 14 is connected directly to a Schmitt trigger 64 while the other end is connected to the mid point of a potential divider formed by resistors 66 and 68 and to capacitor 70. This arrangement sets one end of the coil to half the supply voltage.

Capacitor 70 decouples the junction of resistors 66, 68 to stablise the voltage level of this point. When no signal is being received, the input to the Schmitt trigger 64 is therefore sitting at half the supply voltage. If the threshold voltage of the Schmitt trigger 64 is +2 to 3 volts, the received signal must be in excess of one volt peak to peak to trigger Schmitt trigger 64. This arrangement makes the receiver circuit immune to electrical noise below that level. It is important that no tuned circuit should be connected to the receiver inductor coil as this input circuit has high impedances into the Schmitt trigger 64. If a tuned circuit were used, ringing would occur and true representation of the signal transmitted to the receiver coil would be lost.

Since it would be possible for the received signal to stop either on a high or a low point of any cycle, it is possible for the Schmitt trigger 64 to be left in a high or low condition respectively. To prevent this being passed to the output, a high pass filter formed by a capacitor 72 and resistor 74 is connected to the output of the Schmitt trigger. This filter prevents any DC coupling between the coil and the remainder of the receiver circuit. The filter output is connected to the input of a further Schmitt trigger 76 which is connected via a circuit comprising a resistor 78, diode 80 and capacitor 82, to two further series connected Schmitt triggers 84, 86 coupled by a resistor 88. Finally the output of the Schmitt trigger 86 is connected to a level translator 90 which is connected to a voltage supply to restore the output of the circuit to the required RS232 voltage level.

When the oscillator in the transmitter circuit is operating the receiver coil 14 receives sufficient signal so that the output of the first Schmitt trigger 64 changes in sympathy with the transmitting oscillator. In turn the second Schmitt trigger 76 follows the output of the first. The output of the second Schmitt trigger 76 will be a square wave oscillation of full supply amplitude. The function of the receiver circuit is to convert this oscillating signal to a steady logic "1" level at output 84 and to provide a logic "0" level at an output 92 when no signal is being received from the coupled transmitter circuit.

When no signal is present the output of the second Schmitt trigger 76 will remain high and the capacitor 82 will therefore be charged via resistor 78. The output of the third Schmitt trigger 84 will be low and the output of the fourth high, so that the output of the translator 90, which like all the preceding Schmitt triggers is an inverting device, will be at the RS232 logic "0" level When a signal is being received by the receiver -coil 14, the output of the second Schmitt trigger 76 will oscillate. As the output of 76 goes low during each oscillation period capacitor 82 is discharged via the diode 80. The capacitor 82 and resistor 78 are arranged to have a time constant which 'is about three times the period of the oscillations received so that the capacitor 82 will never become fully charged while oscillation is taking place. Since the third Schmitt trigger senses the voltage on capacitor 82 the trigger level will not be reached and the output of Schmitt trigger 84 will be low and this corresponds to a logic "1" level at the output 92. The oscillation must also have stopped for three periods before the output of Schmitt trigger 84 changes state. This has the advantage of improving noise immunity of the circuit.

The resistor 88 together with the input capacitance of Schmitt trigger 86 provide a delay equivalent to about one oscillation period.

All five Schmitt triggers 54, 64, 76, 84 and 86 in a receiver and transmitter circuit in each connector part may be provided in a single package such as the 74HC14 hex inverter chip. Inverting devices have been employed because these are readily available but it will be appreciated that the use of inverting devices is not a feature of the invention.

Claims (8)

1. A connector device having two parts which mate together with facing plane surfaces of non-magnetic material, each part comprising a transmitter circuit having an input for receiving serial digital data to be transmitted and an output connected to a transmission induction coil mounted behind said plane surface, and a receiver circuit having a receiver induction coil mounted behind said plane surface and connected to a receiver circuit which has an output for received digital data, the transmission coil of one part being aligned with the receiver coil of the other part when the parts are mated.

2. A device according to claim 1, wherein the plane surface of one part is provided in the base of a recess and the plane surface of the other part is provided as the end surface of a plug which fits into the recess.

3. A connector device according to claim 2 wherein the recess and plug are of circular cross-section.

4. A connector device according to claim 2 or 3, wherein an O-ring seal is fitted in a groove formed in a side wall of the plug.

5. A connector device according to any one of the preceding claims, wherein the plane surfaces are formed by walls of fibre reinforced plastics resin, toughened glass or ceramic material.

6. A connector device according to any one of the preceding claims, wherein the transmitter circuit comprises an oscillator circuit connected to the digital data input, and adapted to produce oscillations of a frequency substantially in excess of the maximum data baud rate, when the input is at one only of the two logic levels.

7. A connector device as claimed in claim 6, wherein the receiver circuit comprises means for converting a received sequence of oscillations into a steady output logic level.

8. A connector device substantially as herein described with reference to the accompanying drawings.