Data transfer system.

0001This invention relates to data transfer systems, and particularly, though not exclusively, to code transfer systems.

0002From German Offenlegungsschrift 2453647 there is known a code transfer system in which a code is transmitted from a passive device to an active device in response to the active device transmitting to the passive device a pulsed signal. However, in this known code transfer system the signal from the active device is transmitted on a different frequency than the signal transmitted by the passive device.

0003It is an object of the present invention to provide a data transfer system in which the above disadvantage may be overcome.

0004One code transfer system in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic block diagram of an active component and a passive component of the system; and Figure 2 shows in greater detail the circuitry of the passive component of Figure 1.

0005Referring to the drawings, in a security system a predetermined code is transferred from a passive component to a active component. Such a code transfer may be required in a security system, for example, to allow a person possessing the passive component, or code box, to have access to a restricted area or to initiate a restricted operation such as re-setting an alarm.

0006The active component comprises an oscillator 2 and transmitter 4 controlled by a microprocessor 6, and a receiver 8 and data recovery circuitry 10 whose output is applied to the microporocessor 6.

0007The passive component comprises a receiver 12 and rectifier 14 and timing and reset circuitry 16 and 18. The passive component also includes an oscillator 20 and filter and blanking circuitry 22, together with code circuitry 24 and a transmitter 26.

0008In use, when the passive component is brought into proximity to the active component, the active component transmits an electromagnetic pulse, at a frequency of approximately 1 MHz, to the passive component. The energy in the electromagnetic pulse received by the passive component is recovered by the rectifier 14 to produce a voltage across the terminals U1, UB which activates the other circuitry in the passive component.

0009The pulse received by the passive component also triggers timing circuitry 16 which regenerates therefrom a clock pulse. The regenerated clock pulse is applied to the reset circuitry 18 and to both the filter and blanking circuitry 22 and to the decade counter of the code circuitry 24. The decade counter produces at the first of its outputs Qo an output signal which passes through the diode D1 and is applied to the filter and blanking circuitry 22. The clocked output of the filter and blanking circuitry 22 is applied to activate the transmitter 26 to transmit an electromagnetic pulse (of the same 1 MHz frequency as that from the active component) which is thus representative of the first element of the code defined by diodes D1, D2 and D3 of the code circuitry.

0010When the active component receives the electromagnetic pulse from the passive component it recovers the data (i.e. the code element) therefrom and feeds the code element to the microprocessor 6. The microprocessor stores the code element and then triggers its oscillator to cause the transmission of a further electromagnetic pulse from the active component.

0011Receipt of this further pulse by the passive component causes re-energisation of the passive component, and (in an analogous manner to that described above) causes the passive component to transmit an electromagnetic pulse representative of the next element of the code, as defined by the presence or absence of a diode connected to the next (Q1) output of the decade counter of the code circuitry 24. This pulse is received by the active component, the next element of the code is recovered and appended to the preceding element by the active unit, which then transmits another electromagnetic pulse.

0012This process continues, with the passive unit being repeatedly re-energised by each pulse received from the active component, and with the passive component sequentially transmitting pulses representative of the sequence of elements of the code as defined by the configuration of diodes connected to the outputs of the decade counter of the code circuitry 24.

0013Thus, it will be appreciated, transfer of the code is achieved one element at a time, with the passive component being re-energised by the active component for the transfer of each new element thereto, i.e. the transfer of the code is inter-leaved with the synchronising and energising pulses from the active component.

0014In this way the same transmission frequency can be used for transmission by both the active component and the passive component, and the passive component has no internal power source (e.g. a battery) and so can be smaller, lighter, have no need for replacement or re-charging and can be better sealed and protected against the ingress of external environmental factors such as dirt, water, etc.

0015The code transfer system may be used in a security system of a building in which active units are provided at predetermined locations and security personnel who must regularly visit these locations are provided with individually coded passive units.

0016The security personnel 'check-in' at these locations by bringing their passive code box into close proximity to the active unit (which may, for example, be wall mounted) and the passive unit's code is automatically transferred to the active unit as described above. The active units may then, for example, send the code to a central processing unit (not shown) where the code is logged, together with the time and the location of the relevant active unit.