"Communication set. in particular alarm device" The present invention relates to a communication set, in particular an alarm device, comprising a controller provided to be fixed on an object to be protected and a handset provided to be carried by a user, wherein (a) said controller comprises a controller signal generator connected to a controller transmitter and a controller receiver, (b) said handset comprises a handset signal generator connected to a handset transmitter and a handset receiver, (c) said controller signal generator is provided for generating a controller signal and transmitting said controller signal to said controller transmitter, (d) said controller transmitter is provided for transmitting said controller signal to said handset receiver within a first predetermined distance range, (e) said handset receiver is provided for receiving said controller signal and transmitting said controller signal to said handset signal generator, (f) said handset signal generator is provided for generating a handset signal upon receipt of said controller signal and transmitting said handset signal to said handset transmitter, (g) said handset transmitter is provided for transmitting said handset signal to said controller receiver within a second predetermined distance range, and

(h) said controller receiver is provided for receiving said handset signal and transmitting said handset signal to said controller signal generator.

Such a communication set is known from US patent No.

4,763,121 and used for a keyless entry system allowing fully automatic operation of a door lock device of an automotive vehicle. The controller is thus mounted on a vehicle and the handset is carried by the authorised user of the vehicle. The transmission of signals between the handset and the controller is performed within a predetermined distance range.

If the handset is within the predetermined distance range from the controller, thus if the authorised user is within this predetermined distance range, the controller signal sent by the controller will be received by the handset, which handset will then generate a handset signal and send it to the controller. Upon receipt of this handset signal, the controller will compare the code of the handset signal with a code stored in its memory and operate a door lock device for unlocking when the codes match.

On the other hand, if the handset is outside the predetermined distance range, the controller signal generated by the controller cannot reach the handset, and therefore the handset will not generate said handset signal. Consequently, the controller will detect an absence of the handset signal and operate the door lock device for locking.

The problem of the known communication set is that as soon as the handset is outside the predetermined distance range, signals cannot be transmitted anymore, neither from the controller to the handset, nor from the handset to the controller.

It is therefore an object of the present invention to improve the known communication set and still enables transmission of signals

from the controller to the handset, even when the handset cannot transmit signals to the controller anymore.

To this object, the communication set according to the invention is characterised in that said first predetermined range is at least twice said second predetermined range. By providing that the distance range for signal transmission from the controller to the handset is larger than the distance range for signal transmission from the handset to the controller, it is still possible to transmit signals from the controller to the handset when the handset is located outside said second predetermined distance range, but still within the first predetermined distance range.

In a first preferred embodiment, the communication set according to the present invention further comprises a sensor, wherein said controller signal comprises at least one operational status of said sensor, and wherein said handset further comprises means for generating an audible and/or visible signal upon receipt of said operational status. In particular, said sensor is a motion sensor. This enables to keep the handset user informed about the status of the controller, when he is between the first and second predetermined distance range. In particular, the user will further be warned if the object to be protected is moved from its place.

Preferably, said communication set further comprises a battery for supplying power to said controller signal generator, said controller transmitter and said controller receiver, wherein said controller signal comprises at least one further operational status, in particular a power low indication, of the battery power. In this way, the user is informed when the battery power is weak and thus that the battery should be replace.

In a second preferred embodiment, the communication set is provided to be used for protecting a plurality of objects, said controller signal further comprising an identity parameter for identifying each of

said objects. In particular, said set comprises, for each object to be protected, said controller. This enables to protect a plurality of objects with a same handset and with one controller for each object. According to an alternative said controller is provided to be fixed on one of said objects to be protected, said set further comprises at least one slave device, each slave device being provided to be fixed on one other of said objects to be protected, and said controller is further provided for checking the presence of said slave device.

Preferably, said handset signal generator further comprises powering off means for generating a powering off signal and transmitting said powering off signal to said handset transmitter; said handset transmitter is provided for transmitting said powering off signal to said controller receiver within said second predetermined distance range; and said controller receiver is provided for receiving said powering off signal and transmitting said powering off signal to a controller power control, in particular connected to said battery. This enables to control powering off the controller from the handset and avoids therefore the necessity to use of a special key or the like for switching off the controllers.

In a third preferred embodiment, said handset signal generator further comprises means for generating an opening signal and transmitting said opening signal to said handset transmitter; said handset transmitter is provided for transmitting said opening signal to said controller receiver within said second predetermined distance range, and said controller receiver is provided for receiving said opening signal and transmitting said opening signal to controller opening means for opening a battery compartment.

In a fourth preferred embodiment, said handset is provided for generating a missing object signal if said controller signal is not received by said handset receiver after a predetermined period of time.

This enables to inform the user when the handset does not receive

signals anymore from the controller, which could occur for example when the handset is outside the first predetermined distance range.

The communication set according to the present invention enables thus to perform a diagnosis of the controller operation and to inform the user when a malfunctioning or an alarm situation occurs, in particular low battery level, controller signal not received, one of the objects missing or object moved by an unauthorised person.

The invention will now be described more in detail, referring to the annexed drawings, wherein: Figure 1 illustrates schematically a block diagram of a communication set comprising a controller and a handset according to a preferred embodiment of the invention; Figures 2 to 5 illustrate a possible circuitry of the communication set according to Figure 1.

The following description describes in detail one possible embodiment of the present invention, in particular an alarm device for skis or the like. It will be understood that the communication set according to the present invention can also be used for protecting other objects, such as suitcases. Further, the communication set according to the present invention is not limited to an alarm device. It could also be applied for example as a keyless entry system for automatic operation of a door lock device of an automotive vehicle.

Figure 1 illustrates schematically a communication set according to the present invention, comprising a controller 100 and a handset 200 according to a preferred embodiment of the present invention. The controller 100 comprises a controller signal generator 130 connected to a controller transmitter 110 and a controller receiver 120.

Similarly, the handset 200 comprises a handset signal generator 230 connected to a handset transmitter 210 and a handset receiver 220.

As illustrated in Figure 1, the controller further comprises a power control device 150 connected to the signal generator 130 for controlling and supplying power to the signal generator 130. The power control is switched on by pressing the power on button 151. It cannot be switched off by this button. Switching off the power control and thus the power supply to the controller is performed by pressing a button provided on the handset as will be explained further. Optionally, the controller further comprises a user output device 160 such as a loudspeaker for producing an audible alarm when an alarm signal is generated. More details concerning the alarm signal will be described further.

The handset 200 further comprises a plurality of output devices connected to the handset signal generator 230, including display units 250 and 260 and a loudspeaker unit 270, wherein the loudspeaker unit 270 is provided for generating an alarm sound audible to the user carrying the handset and the display unit 250 is provided for displaying the cause of the alarm to the user. More detail concerning the conditions when the alarm sound and the operation of the display units will be described further.

The controller signal generator 130 is provided for generating a controller signal COSIG and transmitting this controller signal to the controller transmitter 110. To this purpose, the controller signal generator comprises an oscillator 131 provided for periodically generating a pulse 132, for example a pulse of 0.5 sec every 10 seconds, which is transmitted to an encoder 133 and the transmitter 110.

This pulse triggers the encoder 133 and the transmitter 110 for transmitting an encoded controller signal COSIG to the handset receiver 220 within a first predetermined distance range, for example 200 meters.

In particular, the controller signal COSIG comprises a plurality of bits, each bit providing information of the status of a portion of the controller 100. A first bit indicates the status of an alarm signal S1

generated by a motion sensor 136. This first bit is set to value 1 in case the object to which the controller is fixed is moved from its place for a predetermined minimum time, for example 0.5 seconds and in case the alarm disable signal S3 is not generated. More details concerning the alarm disable signal will be described further. A second bit indicates the status of the power control 150, in particular a low power status S2 of the power supply. In case a plurality of controllers are used, such as would be the case for two skis, a number of bits, in this case two bits S4 and S5 are used for identifying the controller and thus the first and second skis.

In this case, the communication set is composed of two controllers and one handset, wherein each controller 100 sends a controller signal to the handset 200. In Figure 1, only one controller has been illustrated.

According to an alternative embodiment, one of the controllers could be a master controller which would essentially correspond to the controller illustrated in Figure 1, but would further be provided for receiving a slave device signal from at least one slave device. In particular, communication between master and slave is performed by means of transponder techniques, known as such. The advantage of such an embodiment is that, when applied for example to skis, the slave device signals must be transmitted over a limited range, which would save power consumption of the slave devices.

The handset receiver 220 is provided for receiving the encoded controller signal COSIG and transmitting this signal to the handset signal generator 230. The controller signal COSIG is decoded by means of decoder 233 which is set to a same key code (key 1) in order to be able to process the controller signal.

In case a valid status is received for both skis, in particular when there is no alarm signal generated and the battery power level is still sufficient, a valid transmission signal VT is generated which will trigger a plurality of actions:

-timer 242 will generate an enable signal S20, which will be transmitted to the handset encoder 232 and the handset transmitter 210; time t2 from timer 242 determines the duration the enable signal S20 will last and thus the transmission duration of the HASIG signal to be transmitted by the handset to the controller. Care should be taken that this time is chosen sufficiently long to allow the controller receiver to decode and verify the integrity of the handset signal. A duration of approximately 0.5 seconds appeared to be sufficient; -a LED 260 will flash for a predetermined time to inform the user that a valid transmission has been received; -signals S21 and S22, indicating the presence status of the first and second skis, are provided for retriggering presence timers 238 and 239, so that the loudspeaker unit 270 and LED 251 of the display unit 250 will be kept off.

The handset transmitter 210 according to the present invention is provided for transmitting a handset signal HASIG to the controller receiver 120. This can be performed within a second predetermined range, for example 2 meters. In general the first predetermined distance range should be at least twice the second predetermined distance range. For example the first range could be 10 meters, whereas the second range should be at least 20 meters. The predetermined distance ranges is dependent of the application of the communication set. In particular, the predetermined distance ranges may be adjustable.

If the handset is located within the second predetermined distance range, in particular within 2 meters, then a handset signal will be generated by the encoder upon receipt of the enable signal S20, which handset signal will be transmitted to the controller receiver 120. In particular, the handset signal HASIG comprises a power off signal S25 which is generated if the user of the handset presses power off switch

241. The received handset signal is transmitted to the controller decoder 132, which decoder will process the signal. The signal can be processed only if the decoder is set to a key (key 2) corresponding to the handset encoder 232 key. If this is the case, a valid transmission signal S9 is generated which will retrigger timer 140 for generating an alarm disable signal S3. The alarm disable signal S3 is transmitted to the alarm generator 141 so as to disable the generation of an alarm signal S1, even if the motion sensor 136 generates a movement signal. This is performed since the authorised user is in the proximity, i. e. within the second predetermined distance range of the object to be protected. If the authorised user moves its skis, an alarm signal S1 will thus not be generated. If the user presses power off switch 241, this information will be incorporated into the handset signal and the controller decoder 132 will generate a power off signal S8 which is sent to the power control unit 150. This enables the authorised user to manually switch off the controller, only if he is in the second predetermined distance range of the controller.

Similarly, a battery compartment opening switch is provided on the handset. This is not illustrated in Figure 1. By pressing such a switch, a battery compartment opening signal would be generated and similarly incorporated into the handset signal. Upon receipt of the handset signal, the controller decoder 132 will decode the signal, provided of course the handset signal comprises the corresponding code (key 2), and supply a signal to the battery compartment for opening the latter. In this way, the battery compartment is only accessible by the authorised user when he is in the proximity of the controller. In this way, it is not necessary to provide a lockable battery compartment to be opened with a special key or the like.

If the handset is located between the first and second predetermined distance ranges, in particular between 2 and 200 meters,

then the controller receiver 120 will not receive the handset signal HASIG from the handset transmitter 210. Since the controller receiver 120 does not receive the handset signal HASIG, the controller decoder 132 will not generate a valid transmission signal S9, nor a power off signal S8, so that the alarm can not be disabled and the controller can not be powered off. The authorised person is now remotely located from the objects to be protected.

In this case, the communication set is automatically switched to an armed or active mode, wherein the controller signal is transmitted to the handset as explained hereinabove. The following situations may occur: -If the motion sensor 136 detects a movement for a predetermined time, an alarm signal S1 will be generated which will activate loudspeaker unit 160 for producing an audible alarm sound. Timer 147 is provided for generating an alarm sound of approximately 10 seconds upon receipt of the alarm signal S1. The handset decoder 233 will generate an alarm signal S23. This alarm signal S23 is transmitted to the loudspeaker unit 270 for generating an audible signal for a predetermined time, for example 10 seconds and also to the display unit 250 for lighting LED 252 indicating what has caused the generation of the audible sound, in this case the movement detected by the motion sensor.

-If the power level from the controller power supply 150 is lower than a predetermined level, a power low signal S2 is generated and transmitted to the handset. The handset decoder 233 detects this signal and generates a power low signal S24. This power low signal S24 is transmitted to the loudspeaker unit 270 for generating an audible signal for a predetermined time, for example 10 seconds and also to the display unit 250 for lighting LED 253 indicating what has

caused the generation of the audible sound, in this case a power low status of the controller power supply.

If signals S21 and S22 fail to appear within a predetermined time, for example due to a malfunction of the controller or the handset or the distance between the controller and the handset is larger than the first predetermined distance range, in particular 200 meters, then an audible alarm signal will be generated by loudspeaker unit 270 and latch 256 will be switched to light LED 251 from the display unit 250. LED 251 provides thus an indication to the user that the reason for the alarm is an absence of a receipt of the controller signal by the handset receiver.

According to a preferred embodiment, the power level of the handset is also checked and if the handset power level is lower than a predetermined value, signal S26 will be generated which will light LED 254 is lit.

In all the cases when a LED 251 to 254 from the display unit 250 is lit, the LED's remain lit until the user presses reset button 255, which will control latch 256 for disabling the LED's. In this way, it is guaranteed that the user intentionally switched off the LED's after he has checked the cause why the audible sound has been generated.

Preferably, the controller is provided with channel free check means, so as to allow operation of several communication sets in a same environment. When presence oscillator 131 times out, it triggers the handshake sequence between controller and handset as explained hereinabove. The positive pulse 134 enables receiver 120 through an OR circuit 149. If another transmitter would be active, the receiver would supply a pulse S6 to timer 143, which timer would stretch this pulse to a signal S7 having a duration t provided for disabling the transmission of the controller signal. The AND circuit 144 is provided for holding off any transmission enable signal coming from timer 146. If the transmission

channel is free, pulse S6 will not be present and thus signal S7 will enable transmission when the presence oscillator generates a pulse 134.

The falling edge of pulse 134 triggers timer 146 whose time t determines the transmission duration of the controller signal COSIG.

Time t must be chosen sufficiently long to allow the handset receiver to decode and verify the controller signal integrity. In this case, a duration of approximately 0.3 seconds is suitable. If signal S7 enables transmission, S10 will switch to true to perform the transmission.

The falling edge of S10 triggers timer 142 wherein t2 represents the time window within which the handset has to respond.

The controller receiver 120 is enabled through OR gate 149.

In order to save the controller power consumption, the transmitter 110 and the receiver 120 are only switched on when they are needed. This is also performed by the enable signal S10 for the transmitter and the signal generated by the OR gate 149 for the receiver.

In case an alarm signal S1 is generated, as a consequence of a movement detected by the motion sensor 136, the enable signal S10 is also generated. This is for example achieved by providing an OR gate 145 having as input the presence pulses 132 generated by the oscillator 131 and the alarm signal S1 generated by the motion sensor 136. In case one of the two signals are active, the enable signal S10 is generated. Consequently, the alarm signal overrules the generation of the enable signals according to a predetermined cycle.

A further aspect of the present invention deals with location of the missing objects. In case the skis are stolen, it would be desirable to detect the location of the skis. This is performed by detecting from which direction the controller signal COSIG comes from. For this purpose, a direction sensitive antenna is used and the handset is switched to a detection mode. By slowly sweeping the handset from left to right and vice versa, it is possible to determine the highest signal

strength of the controller signal. When the highest signal strength has been reached, LED 260 flashes, indicating to the user that his skis are located in that direction. By executing this operation from two different angles, a technique which is known as triangulation, the exact location of the skis can approximately detected.

The invention will now be described referring to Figures 2 to 6, which illustrate one possible way implementing the communication set according to Figure 1. To allow operation at low temperatures and in order to comply to EMC, preference has been given to CMOS technology instead of using a microcontroller. Using CMOS technology also enables to reduce the power consumption.

The power source must also resist to low temperature conditions. For this purpose use is preferably made of an alkaline battery.

All circuitry has been designed for minimal power consumption. To this end, high resistance and low capacitor values have been chosen (order of magnitude of kQ and nF or pF such as indicated in Figures 2 to 5). For AND and OR gates, passive components have been used.

Referring to Figure 2, the circuit relating to the motion sensor and the generation of an alarm signal is shown. To obtain three dimensional sensitivity, three linear motion detectors MS1 to MS3 are placed perpendicular to each other. The employed motion detectors are for example of the standard commercial available mercury free inclination switch type. The signal conditioning combines the signals and generates a pulse on both the breaking or the making of a motion sensor contact. Since operation of MS1 to MS3 is similar, the circuit around MS1 is explained.

Assume motion makes MS1 to switch from a closed to an open state, then resistance R3 will pull node N1 to the high state. Since

C1 and C3 were discharged in the previous state (MS1 was closed and thus connected to ground on one side and through R1 and R4 at the other side), C1 and C3 will now charge. The charging currents will induce positive proportional voltages across R1 and R4. Due to D1, the voltage across R1 will have no further effect, but the voltage across R4, as it rises above 0.6 V, will drive T1 to a conductive state pulling node N2 low for the time it takes to charge C3 through R3 in series with the parallel circuit of R4 and the input impedance of T1 (R3 + (R4//hie T1)).

In this way, a pulse is obtained for the opening state of MS1.

Now the closing pulse will be explained, i. e. MS1 switches from the open state to the closed state. From the previous state, we know that C1 and C3 are charged. The closing of MS1 will discharge C1 and C3 and induce negative proportional voltages across R1 and R4.

The negative voltage across R4 will have no further effect. However N2 will be pulled down through D1 for the time it takes to discharge C1 through R1 in parallel with R2 (R1 II R2) in accordance with their potential difference.

Consequently, the circuitry delivers a negative pulse at node N2 for both the breaking and the making of a contact of MS1. The described part of the circuitry corresponds to block 136 referred in Figure 1.

Circuitry 141 processes the motion signal and the alarm disable signal. Since T2 acts as an inverter, each positive pulse at node N3 will charge C51 through D51. The amount of charge is determined by R22. R51, on the other hand, is provided for discharging C51. The result of this is that sufficient frequent signals from the motion sensors are required to charge C51 to above the lower threshold voltage of inverting Schmitt trigger U1: A. This filters out spurious motion pulses, in order to avoid false alarms.

If the pulses are sufficiently frequent, the negative pulse signal propagates along two paths: the local audible alarm circuits 147 and 160 and the transmission circuit for transmitting the signal to the controller encoder.

The pulse stretching circuit in circuit 147 works as follows : capacitor C15 is discharged through diode D7, pulling Schmitt trigger U1: E below the lower threshold. Consequently, the output of the Schmitt trigger goes high until resistance R15 has charged capacitor C15 above the upper threshold. This high signal is first provided for activating the audible alarm (resistance R60) and its driver transistor T60 and resistance T60.

A further function of the high signal is to disable further alarm pulses. C51 is kept discharged by the low output of U1: C through D50 while the audible alarm timer 147 drives the audible alarm. If the audible alarm timer has ran out, the U1: E output goes low again and U1: C output goes high. Since the voltage across C51 is lower than at the output of U1: C, diode D50 does not conduct, leaving the operation of C51 unaffected. This portion of the circuitry should preferably be used, because the intense sound of the audible alarm also triggers the motion sensor making the alarm sound forever if such a circuitry was not provided.

The D9, R23, C10, U1: F circuit acts as a pulse stretcher similar to the circuit 147, but with other values so that the alarm pulse output by Schmitt trigger U1: F will last for about 1.5 seconds, which alarm pulse is supplied to the encoder 133 and to the OR circuit 145 for starting the alarm transmission to the handset.

When the authorised user is within the second predetermined distance range, the alarm signal should not be generated as described hereinabove. For this purpose, circuitry 140 is provided.

When a valid transmission signal S9 is received by the controller

decoder 132, a positive pulse is supplied to capacitor C11 charging the latter above the threshold value from Schmitt trigger U1: B, switching its output low and therefore also pulling low C51 through diode D10.

Consequently, the alarm is disabled. If no valid transmission occurs, resistance R9 will discharge C11 for about 5 seconds below the lower threshold of U1: B, switching its output to high and leaving the operation of C51 unaffected since D10 does not conduct.

Figure 3 illustrates the controller receiver, transmitter and a portion of the signal generator.

The circuit around U2: A acts as presence oscillator with a 0.1 second pulse and a 2 seconds pause ratio at its output <1>. The pulse time is determined by R8, D2 and C23, whereas the pause time is determined by R7, D3 and C23. Consequently, every two seconds, a handshake sequence with the handset is performed.

The positive pulse generated by the presence oscillator enables the receiver through U2: F which pulls down D14 of the OR circuit 149. The OR circuit is an inverted logic OR circuit comprising resistance R25 and diodes D13 and D14. By pulling down D14, T7 is conductive which will feed receiver 120.

If another transmitter would be active, the signal S6 coming from the receiver RX1 pin DO would activate circuit 143 which is a pulse stretcher. Signal S6 will charge capacitor C14 through diode D12 and resistance R27. The circuit formed by R27 and C14 is a low pass filter for filtering out spikes. If C14 is charged above the upper threshold of Schmitt trigger U2: B, its output switches to low until resistance R28 has discharged C14 below the lower threshold of U2: B. This will pull down the output of the NAND circuit 144, holding off the transmission.

The falling edge of the presence pulse output by the presence oscillator 131 triggers circuit 146 which is a differentiator pulse

generator. Since resistance R26 connects the input of Schmitt trigger U2: E to Vcc, a falling edge at capacitor C13 will generate a positive pulse of approximately 0.3 seconds at the output of U2: E i. e. until resistance R26 has charged C13 above the upper threshold of U2: E. The duration of this pulse determines the controller signal COSIG transmission time.

If no other transmitter is active, the input 4 at Schmitt trigger U2: B will remain low and U2: E will not pull down output 6 from the NAND circuit 144 through diode D8 any more, resulting in a positive pulse coming out of the NAND circuit 144. This signal directly switches the OR circuit 145, consisting of diodes D5 and D6 and resistor R11. The positive pulse at the NAND output 6 drives D6 into conduction. The current through D6 and resistor R11 induces a driving voltage for the encoder 133 at pin TE and at Schmitt trigger U2: C.

In case an alarm signal is generated, the output of the OR circuit will be high through D5, so that any hold off signal is overridden and the transmission is started in the same way.

When the signal at TE is high, the encoder 133 is enabled and U2: C drives, through resistance R10, the transmitter supply switch T3 which finally feeds the transmitter.

As a result of this, the actual status is supplied to the encoder 133, including the ski identifier (pins AD12 and AD13) and the power level status (pin AD15). Key 1 (pins AO to A9) is provided for encoding the controller signal COSIG, which is supplied to the transmitter 110 for transmitting the controller signal to the handset.

On the falling edge of the OR circuit 145 output 7, which appears as a rising edge at capacitor C24, timer 142 is triggered which is a differentiator pulse generator. Since resistance R14 connects the input of Schmitt trigger U2: D to ground, a rising edge at capacitor C24 will generate a negative pulse of about 0.5 seconds at the output of U2: D, i. e. until resistance R14 has discharged capacitor C24 below the lower

threshold of U2: D. The pulse duration at the output of U2: D determines the reception time within which a response is expected. The output of timer 142 pulls down diode D13 of the OR circuit 149, which drives T7 to feed the receiver; If an authorised handset is within the second predetermined distance range, in particular within 2 meters, its response (the handset signal HASIG) is decoded using key2 (pins AO to A9 in decoder 132) and used to either entirely switch off the controller by generating a pulse at the D15 pin (if the user has pressed the power off button 241 as explained hereinabove) or to disable the alarm by generating a valid transmission pulse VT at the VT pin of decoder 132. If the user has pressed battery compartment opening switch, a pulse will be generated at D14 pin to open the battery compartment, so that the authorised user may replace the battery. This terminates the transmission sequence.

The power level check forms a portion of the power control unit 150 and has therefore been referenced as 150'. It comprises a Zener diode ZD2, which is biased to its Zener voltage by resistance R21.

Since the cathode of ZD2 is connected to the voltage source Vcc, the voltage at the input of U1: D is shifted from Vcc by the Zener voltage Vz.

Consequently, the output of U1: D, switches to high if Vcc minus Vz drops below the lower threshold of U1: D. The capacitor C2 is provided for power on initialisation.

For obtaining the two different predetermined distance ranges, the transmitted power is controlled through antenna design and the sensitivity of the antenna is controlled for example by providing a shorter antenna for the smaller range. As antenna for the handset and the controller, use can be made of a helical antenna. The density of the windings of such an antenna may be used for controlling the sensitivity.

Figures 4 and 5 illustrate a possible circuitry for the handset illustrated in Figure 1.

During operation of the device, the receiver remains switched on in order to receive the controller signal, periodically transmitted by the controller (s). Resistor R3 pulls the input of Schmitt trigger U4: D to ground. Consequently, the output of U4: D is high and therefore the output of U3: C is low, drawing the base current from transistor T2, which drives the latter to conduction for supplying power to the handset receiver 220. The other signal paths are explained further.

In case a controller signal COSIG is received, this signal is transmitted from output pin DO from the receiver 220 to an input pin DI from the decoder 233. In case the key embedded in the controller signal matches the key set at the decoder (at pins AO to A9), then the outputs SKI1 (pin D12), SKI2 (pin D13), ALARM (pin D14) and PWRLOW (pin D15) are updated and decoder pin VT goes high indicating that a valid controller signal has been received. The signal is inverted in U4: C and passed to LED LD5 from display unit 260providing to the user visual information that a valid transmission has been performed and to timer 242.

On the falling edge of the valid transmission pulse VT, a rising edge is present at the input of capacitor C2 and timer 242 is triggered, which timer forms a differentiator pulse generator. Since resistance R3 connects the input of U4: D to ground, a rising edge at capacitor C2 will generate a negative pulse for approximately 0.5 seconds at the output of U4: D, i. e. until R3 has discharged C2 below the lower threshold of U4: D. The duration of this pulse determines the transmission time.

During the negative pulse coming from U4: D, three actions are performed.

First, through resistance R2, a base current is drawn from transistor T1 driving it to conduction and thus feeding the transmitter 210. The output of U3: C goes high.

Second, a transmit enable pulse is supplied to the encoder 232 (pin TE), which initiates the generation of the handset signal HASIG.

The output pin DO of the encoder 232 is linked to the handset transmitter 210 at pin Al, by means of which the data are transmitted to the controller receiver.

Third, when U3: C goes high, no more base current is drawn from transistor T2 through resistance R14, driving transistor T2 out of conduction and shutting down the power supply for the receiver 220.

When the encoder generates an encoded message, i. e. an encoded handset signal HASIG, it comprises the a power off PWROFF status, i. e. it indicates whether or not the power off switch 241 has been pressed by the user. If the status is true, the controller uses this status for powering off the power control (see S8 and 150 in Figure 1).

Since both key1 and key2 have to correspond for both the handset signal and the controller signal to allow switching off the controller, the statistical error is reduced to an insignificant value. For generating an alarm signal at the handset, the statistical error is based on the number of key settings of key1. When use is for example made of encoders of the commercial available Holtec HT600 series, the number of key settings is 118098. The statistical error for the alarm signal is in this case 1/118098 or approximately 8.5 x 10, and for the powering off signal 1/1180982 or approximately 7 x 10-".

To check the presence of two skis, two ski presence timers 238 and 239 are provided. Both have the same function, therefore only timer 238 is described in detail. In order to keep the output from U3: B low, regular positive pulses are required to discharge capacitor C5 through D4. These pulses come from the decoder 233 and are as S21 and S22. If the presence pulse fail to occur for about 10 seconds, resistance R8 will charge C5 below the lower threshold of U3: B, its

output will be high signalling that the ski is missing through the passive OR gate formed by D3, D8 and R22.

Loudspeaker unit 270 is driven by its corresponding timer 235. The timer makes the audible alarm sound signal from the moment C6 is discharged through D6 below the lower threshold, until C6 has been charged through R7 again above the upper threshold. This general alarm signal is the result of the OR gate 234 comprising diodes D1, D2, D5 and D7 and resistance R9, inverted by U3: F. This means that if one of the alarm signals-ski missing (S21 or S22), alarm (S23), controller power low (S24) or handset power low (S26)-coming from the decoder 233 goes high, the audible alarm will sound for approximately 5 seconds.

To inform the user what has caused the alarm, the bit triggering the alarm is stored in one of the SR flip flops 256. The information remains stored and the corresponding LED 251 to 254 remains lit until the user has pressed reset button 255 for resetting all the flip flops 256. Since 256 requires positive logic, this is performed by resistance R12 pulling the reset inputs R1 to R4 from the flip flops to ground GND to allow a latch function, whereas when reset button 255 is pushed, inputs R1 to R4 from the flip flops are pulled to Vcc, resetting all the outputs Q1 to Q4. C151 is provided for power on reset.

This circuitry is further provided with handset power check 280 operating in a same manner as the power level check 150'from Figure 3.

REFERENCES IN FIGURE 1 100 controller 110 controller transmitter 120 controller receiver 130 controller signal generator 131 presence oscillator 132 controller decoder 133 controller encoder 134 pulse 136 motion sensor 140 retriggerable timer 141 alarm generator <BR> <BR> 142 timer<BR> <BR> 143 timer 144 NAND circuit 145 OR circuit <BR> <BR> 146 timer<BR> <BR> 147 timer 149 OR circuit 150 power control device 151 power on switch 160 loudspeaker unit 200 handset 210 handset transmitter 220 handset receiver 230 handset signal generator 232 encoder 233 decoder 234 OR circuit 235 timer 238 retriggerable timer 239 retriggerable timer 241 power off switch 242 timer 250 display unit 251 missing objet LED 252 alarm LED 253 controller power low LED 254 handset power low LED 255 reset button 256 latch 260 display unit 270 loudspeaker unit COSIG controller signal HASIG handset signal S1 alarm signal S2 power low status S3 alarm disable signal S4 identifier ski 1 S5 identifier ski 2 S6 handset signal status S7 channel free signal S8 power off signal S9 valid transmission signal S10 enable signal S20 enable signal S21 ski1 presence signal S22 ski2 presence signal S23 alarm signal S24 controller power low signal S25 power off signal <BR> <BR> S26 handset power low signal