GB2067323A

GB2067323A - Radio transmitter

Info

Publication number: GB2067323A
Application number: GB8100264A
Authority: GB
Original assignee: Mastiff Security Systems Ltd
Current assignee: Mastiff Security Systems Ltd
Priority date: 1980-01-07
Filing date: 1981-01-06
Publication date: 1981-07-22
Also published as: GB2067323B

Abstract

This radio transmitter is for use in an access control system and comprises a hands-free pocket token arranged to transmit bursts of oscillations at a preset carrier frequency with a preset number of carrier frequency cycles in each burst. The transmitter is controlled by a logic circuit driven from a counter 18 of the number of oscillations of an oscillator 11 both in a transmission burst and in the interval between bursts, so that a particularly simple system is provided which can be easily reset in accordance with requirements. <IMAGE>

Description

SPECIFICATION Radio transmitter This invention relates to radio transmitters and one object is to provide a control for such a transmitter, enabling the transmitter to transmit in bursts consisting of a preset number of carrier frequency cycles, separated by intervals for a different preset number of cycles. One application is to the access control system, the subject of British Patent Specification No 1528901 in which the identity of the holder of a token incorporating a radio transmitter is established by the number of carrier frequency cycles in each burst, which number will differfrom token to token, and so from individual to individual.

According to the present invention, a control for a radio transmitter includes a gate for controlling the supply of oscillations to an output, the gate being controlled by a logic circuit operated by a counter of the oscillations, to be open for a preset number of oscillations. In the system described above, the number of oscillations during which the gate is open-which will identify the transmitter-will be substantially greater than the number of oscillations during which the gate is closed, which merely represents a break between bursts of oscillations to be countered.

A single counter can be fed with oscillations and can feed two parallel logic paths which together control the gate.

The invention may be carried into practice in various ways, and one embodiment will now be described by way of example, with reference to the accompanying drawing, of which the single figure is a block diagram of a circuit of a radio-transmitter.

The transmitter includes a CMOS oscillator 11 tuned to the desired carrier frequency, and arranged to supply its output through a gate 12, to an amplifier and transmitter indicated generally at 13, and including a resonant circuit 14tuned to the carrier frequency. Oscillations are only supplied to the transmitter 13 when the gate 12 is open, by virtue of a 1 pulse on an input from a pair of logic paths 15 and 16.

The output from the oscillator 11 is fed to a second input to the gate 12, and also to the input 17to a counter 18. Two coded outputs from the counter 18 depending on the preset number of carrier frequency cycles in the bursts of transmission, and in the intervals between bursts respectively, are connected to control AND gates 19 and 21, respectively in the two logic paths 15 and 16. Each of the AND gates 19 and 21 has its output connected through a recitifier to the reset terminal 22 of the counter 18, so that when either count is achieved the counter is reset and starts again to count the other number.

The outputs of the AND gates 19 and 21 are also connected each to one input of its respective NOR gate 23 or 24. The output of the NOR gate 23 is fed backto one input of the AND gate 19, and to one input of the NOR gate 24. The output of the NOR gate 24 is fed to one input of the AND gate 12 and also to one input of the NOR gate 23.

If there is an '0' at the output of the NOR gate 24, so that the AND gate 12 is closed, and oscillations are not delivered to the transmitter 13, there will be a 1 at the input to the AND gate 19, and a signal from the counter 18 when the count corresponding to the number of cycles between bursts has been achieved will reset the- counter at 22, and will produce a '0' at the output of the NOR gate 23, which will in turn produce a 1 at the output of the NOR gate 24 to open the AND gate 12, and to produce a '0' at the input to the AND gate 19, which is therefore held closed.The counter 18 counts pulses at 17, until the count corresponding to the set number of cycles in a burst has been achieved, when the counter is arranged to provide a 1 to all the inputs at the AND gate 21, which therefore delivers a 1 to the NOR gate 24 which delivers a '0' to close the AND gate 12 to further oscillations, and to the NOR gate 23 whose output changes to 1 which appears at the AND gate 19. At the same time the counter 18 is reset at 22 from the output of the AND gate 21 to start counting the interval again.

It will be appreciated that this is a simple circuit for achieving the desired result, which is independent of variations in frequency of the oscillator, which thus does not have to be an expensive item.

The lengths of the two time intervals in terms of number of pulses, can be easily reset, by connecting appropriate coded outputs from the counter 18 to the two AND gates 19 and 21.

For original setting up and tuning of the transmitter 13 to the oscillator 11, all three inputs of the AND gate 12 can be connected together to the output of the oscillator.

The count is very accurate, and a large number of different identities differing one from another perhaps only by a cycle or two in a burst, can be used on the system. A count of 500 of 1500 is possible.

The transmitter is embodied in a pocket token capable of operating continuously while in the wearer's pocket to generate signals which can be picked up at a loop where access is to be controlled.

The receiver can be as described in Specification No.

1528901.

The system is also useful as an adjunct to the access control systems, the subject of British Patent Specification Nos. 1414119 and 1414120, which give an access signal when they recognise that a particular frequency is present at a pick-up point. In addition to the identification that the transmission is at the particular frequency, there can be the means of identifying the token by the number of carrier frequency cycles in a burst in accordance with this invention.

The circuit can be easily reset for a different frequency or a different number of cycles in a burst, by adjusting respectively the oscillator 11 and the connections to the AND gate 21 from the counters 18.

1. A radio transmitter including a gate for controlling the supply of oscillations to an output and a logic circuit operated by a counter of the oscillation

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Radio transmitter This invention relates to radio transmitters and one object is to provide a control for such a transmitter, enabling the transmitter to transmit in bursts consisting of a preset number of carrier frequency cycles, separated by intervals for a different preset number of cycles. One application is to the access control system, the subject of British Patent Specification No 1528901 in which the identity of the holder of a token incorporating a radio transmitter is established by the number of carrier frequency cycles in each burst, which number will differfrom token to token, and so from individual to individual. According to the present invention, a control for a radio transmitter includes a gate for controlling the supply of oscillations to an output, the gate being controlled by a logic circuit operated by a counter of the oscillations, to be open for a preset number of oscillations. In the system described above, the number of oscillations during which the gate is open-which will identify the transmitter-will be substantially greater than the number of oscillations during which the gate is closed, which merely represents a break between bursts of oscillations to be countered. A single counter can be fed with oscillations and can feed two parallel logic paths which together control the gate. The invention may be carried into practice in various ways, and one embodiment will now be described by way of example, with reference to the accompanying drawing, of which the single figure is a block diagram of a circuit of a radio-transmitter. The transmitter includes a CMOS oscillator 11 tuned to the desired carrier frequency, and arranged to supply its output through a gate 12, to an amplifier and transmitter indicated generally at 13, and including a resonant circuit 14tuned to the carrier frequency. Oscillations are only supplied to the transmitter 13 when the gate 12 is open, by virtue of a 1 pulse on an input from a pair of logic paths 15 and 16. The output from the oscillator 11 is fed to a second input to the gate 12, and also to the input 17to a counter 18. Two coded outputs from the counter 18 depending on the preset number of carrier frequency cycles in the bursts of transmission, and in the intervals between bursts respectively, are connected to control AND gates 19 and 21, respectively in the two logic paths 15 and 16. Each of the AND gates 19 and 21 has its output connected through a recitifier to the reset terminal 22 of the counter 18, so that when either count is achieved the counter is reset and starts again to count the other number. The outputs of the AND gates 19 and 21 are also connected each to one input of its respective NOR gate 23 or 24. The output of the NOR gate 23 is fed backto one input of the AND gate 19, and to one input of the NOR gate 24. The output of the NOR gate 24 is fed to one input of the AND gate 12 and also to one input of the NOR gate 23. If there is an '0' at the output of the NOR gate 24, so that the AND gate 12 is closed, and oscillations are not delivered to the transmitter 13, there will be a 1 at the input to the AND gate 19, and a signal from the counter 18 when the count corresponding to the number of cycles between bursts has been achieved will reset the- counter at 22, and will produce a '0' at the output of the NOR gate 23, which will in turn produce a 1 at the output of the NOR gate 24 to open the AND gate 12, and to produce a '0' at the input to the AND gate 19, which is therefore held closed.The counter 18 counts pulses at 17, until the count corresponding to the set number of cycles in a burst has been achieved, when the counter is arranged to provide a 1 to all the inputs at the AND gate 21, which therefore delivers a 1 to the NOR gate 24 which delivers a '0' to close the AND gate 12 to further oscillations, and to the NOR gate 23 whose output changes to 1 which appears at the AND gate 19. At the same time the counter 18 is reset at 22 from the output of the AND gate 21 to start counting the interval again. It will be appreciated that this is a simple circuit for achieving the desired result, which is independent of variations in frequency of the oscillator, which thus does not have to be an expensive item. The lengths of the two time intervals in terms of number of pulses, can be easily reset, by connecting appropriate coded outputs from the counter 18 to the two AND gates 19 and 21. For original setting up and tuning of the transmitter 13 to the oscillator 11, all three inputs of the AND gate 12 can be connected together to the output of the oscillator. The count is very accurate, and a large number of different identities differing one from another perhaps only by a cycle or two in a burst, can be used on the system. A count of 500 of 1500 is possible. The transmitter is embodied in a pocket token capable of operating continuously while in the wearer's pocket to generate signals which can be picked up at a loop where access is to be controlled. The receiver can be as described in Specification No. 1528901. The system is also useful as an adjunct to the access control systems, the subject of British Patent Specification Nos. 1414119 and 1414120, which give an access signal when they recognise that a particular frequency is present at a pick-up point. In addition to the identification that the transmission is at the particular frequency, there can be the means of identifying the token by the number of carrier frequency cycles in a burst in accordance with this invention. The circuit can be easily reset for a different frequency or a different number of cycles in a burst, by adjusting respectively the oscillator 11 and the connections to the AND gate 21 from the counters 18. CLAIMS

1. A radio transmitter including a gate for controlling the supply of oscillations to an output and a logic circuit operated by a counter of the oscillation and controlling the gate to be opened for a preset number of oscillations and then to be closed.

2. A transmitter as claimed in Claim 1 in which the logic circuit is controlled to be closed for a preset number of oscillations.

3. Atransmitter as claimed in either of the preceding claims including a controllable frequency oscillator.

4. A transmitter as claimed in any of the preceding claims including a single counter arranged to be fed with the oscillations with its output connected to two parallel logic paths which together control the gate.

5. Atransmitter as claimed in Claim 4 in which the two logic paths are connected to different output terminals of the counter.

6. A transmitter as claimed in any of the preceding claims embodied in a hands-free pocket token capable of transmitting oscillations while in the pocket of the user.

7. An access control system including a radio pick-up at at least one location and at least one transmitter as claimed in any of the preceding claims with means for controlling access or giving an alarm in dependence upon whether a person at the location is carrying a transmitter giving bursts of oscillations with the right number of oscillations in each burst.