EP1859421B1

EP1859421B1 - Multi channel child monitor and method

Info

Publication number: EP1859421B1
Application number: EP06710008A
Authority: EP
Inventors: Liu Chi Cheung; David Gooch
Original assignee: Jackel International Ltd
Current assignee: Jackel International Ltd
Priority date: 2005-03-11
Filing date: 2006-03-06
Publication date: 2008-10-15
Anticipated expiration: 2026-03-06
Also published as: ATE411582T1; GB0505069D0; DE602006003195D1; EP1859421A1; CA2599527A1; AU2006221847A1; WO2006095152A1

Abstract

A multi channel child monitor unit is provided comprising a multi channel transmitter and an identifier signal generator. The identifier signal generator is controllable to generate an identifier signal for triggering adoption by a receiver unit of a channel which carries the identifier signal. The multi channel transmitter is controllable to transmit on one of a plurality of transmission channels and to transmit the generated identifier signal on that transmission channel. The identifier signal generated is modulated onto a transmission channel signal.

Description

The invention relates to a multi channel child monitor and method.
Various child monitor systems are known for example portable monitors for use in monitoring the sounds of a baby or a young child. Such monitors typically consist of a radio frequency (RF) transmitter unit which is placed in close proximity to the child being monitored, and an RF receiver unit, which is placed in close proximity to the carer carrying out the monitoring. The transmitter unit transmits sound from the child's environment over an RF wireless link to the receiver unit such that the carer can listen in.
Known baby monitors use pre-determined frequencies or "channels" which can be selected by the carer, to allow monitoring through one frequency or channel. Multiple channels are required in case nearby transmitter-receiver pairs interfere with one another. To avoid receiving this interference it is necessary to change channels on one of the transmitter-receiver pairs. See for example GB 2,346,042 .
Conventionally changing the channel involves switching both the transmitter and receiver units in the pair to an alternative pre-determined "channel". However because of the inconvenience of having to change both units in the pair this action is often not taken. This means that in some cases the "switching" is only partly complete, when only one unit is switched over. This creates a risk of further interference or communication failure between the units in the pair. This situation can be made more complex as in many cases multi channel units have a large number of channels to reduce the risk of interference from similar nearby systems.
Additionally, conventional channel-changing methods, often require a 'handshake' operation, wherein the receiver unit and transmitter unit must verify their identities with one another before a communication link can be established between the two. This operation can be unnecessarily time consuming and can introduce undue complexity into the child monitor system.
The invention is set out in the attached claims. As a result of the provision of a controller associated with a multi channel transmitter which sends an identifying signal on a selected transmission channel, a receiver can search and lock onto the channel carrying the identifier signal such that the receiver unit automatically tracks channel changes signalled by the transmitter unit.
Embodiments of the invention will now be described by way of example, with reference to the drawings of which:

Figure 1 is a schematic diagram of a transmitter-receiver pair in a child monitor system;
Figure 2 is block diagram showing the components of a transmitter unit according to the invention;
Figure 3 is a block diagram showing the components of a receiver unit;
Figure 4 is a flow diagram showing the steps followed in the transmitter unit; and
Figure 5 is a flow diagram showing the steps followed in the receiver unit.

In overview the invention comprises a multi channel child monitor system of the type shown in Figure 1 comprising a child transmitter unit 100 and a parent receiver unit 102. The transmitter unit generates as a pilot tone an identifier signal which it modulates onto a channel carrier signal. When the channel is changed at the transmitter unit 100 for example because of interference from a nearby transmitter-receiver pair then the pilot tone is imposed on the new channel. At the receiver unit 102, an identifier signal detector scans all of the channels to detect the pilot tone and locks onto the channel carrying the pilot tone. As a result the receiver unit automatically tracks any changes in channel triggered at the transmitter unit such that it is not necessary to switch both units. In the meantime the information signal itself, for example the sounds picked up at the transmitter unit are also sent over the channel such that the receiver can broadcast the sound to the carer.
Referring to Figure 2, the transmitter unit designated generally 200 includes a radio transmitter 202 which transmits an RF signal via an antenna 204. The radio transmitter receives an input carrier frequency signal from a crystal oscillator 206, an information signal comprising an audible environmental sound (audio) signal from a microphone 208 and a pilot tone identifier signal from a pilot tone generator 210. The crystal oscillator 206 is a variable frequency oscillator controlled for example, by a phase locked loop (PLL) and switchable between carrier frequencies representing different channels by a channel selector switch 212. As a result sounds from the environment are fed as signals to a modulation input of the radio transmitter 202 and transmitted by the radio transmitter 202 via the antenna 204.
Referring to Figure 3, the modulation signal is picked up by a receiver unit 300 via an antenna 302 which feeds the signal to a radio receiver 304. The radio receiver channel frequencies are governed by a local oscillation frequency crystal oscillator 306 again a variable frequency oscillator controlled for example, by a phase locked loop (PLL). The radio receiver 304 outputs the received signal to a muting control component 309 and an automatic channel selector logic controller 308. The muting control 309 feeds an audio signal in a non-mute mode to an audio amplifier 310 and the audio signal is broadcast by a speaker 312. The logic controller 308 controls the muting control 309 between a mute and non-mute state as described in more detail below. The logic controller further controls the receiver channel frequency as governed by the oscillator 306, again as discussed in more detail below. Optionally the logic controller is further associated with a data storage means 314 storing identifier signal data.
Operation of the system can be further understood with reference to Figures 4 and 5. Figure 4 shows the steps performed at a transmitter unit. At step 400 the channel is selected on the transmitter unit. This is typically done manually when the user recognises that a search is taking place. The controller for example comprised within the channel selector switch 212 controls the crystal oscillator 206 accordingly to ensure that the radio transmitter transmits on the selected channel carrier frequency. At step 402 a transmitter unit modulates the carrier frequency with the information signal comprising the audio signal received at microphone 208. It will be appreciated that although a simple modulation scheme is one option, any appropriate manner of carrying the information signal on the relevant channel can be adopted as will be apparent to the skilled reader. Further the information signal can carry any relevant information on the respective channel.
At step 404 the transmitter unit modulates the carrier signal with the pilot tone identifier signal from the pilot tone generator 13. The pilot tone can be any appropriate signal, for example a predetermined frequency which will be recongisable at the receiver unit or a coded signal using techniques such as OOF (on-off) modulation, FSK (frequency shift keying) modulation or any other appropriate coding scheme. The scheme adopted is preferably selected so as to be easily separated from the information signal by appropriate means such as a frequency filter. Furthermore the pilot tone can simply be any signal identifiable by the receiver unit or can carry additional information such as the identity of the channel selected, or a unique code common to the transmitter-receiver pair to ensure that pilot tone signals from nearby transmitter-receiver pairs will not be identified as the correct signal inadvertently. Similarly the pilot tone can be the same for all channels in which case a simple tone generator can be adopted. Conversely different tones can be used for different channels and different information carried as appropriate for example under the control of a controller included in the channel selector switch or elsewhere the transmitter unit 200. Furthermore the pilot tone can be generated as a constant tone, intermittently or only upon a channel change as long as the receiver unit logic is correspondingly adopted. Furthermore the pilot tone can be set on the respective channel in any appropriate manner, for example by being modulated onto a separate frequency within a defined channel band.
In one optimization, the information signal is constantly imposed on the carrier frequency and a simple pilot tone is constantly generated ensuring minimal control logic and memory is required.
In block 406 the transmitter unit logic for example the channel selector 212, monitors for further changes in channel as discussed above and upon detection of a change repeats the steps described above.
Referring now to Figure 5, the steps carried out at the receiving unit can be further understood. In block 500 the radio receiver 304 selects a first channel under the control of controller 308 and crystal oscillator 306. In block 502 the received signal is filtered, demodulated or otherwise processed as appropriate to detect whether any pilot tone is received. In block 304 the controller 308, acting as an identifier signal pilot tone detector, establishes whether the pilot tone has been detected. If not then the controller 308 controls the receiver 304 and oscillator 306 to scan the next channel, as when the transmitter and receiver unit are on different channels, the signal from the transmitter is no longer synchronised with the receiver such that the receiver either receives a distorted signal from the transmitter operating on a nearby channel or else it just receives white noise. In addition the step of identifying whether the pilot tone is detected may require access to the data storage means 314 by the controller of 318 to compare any received demodulation pilot tone signal with stored values to ensure that the correct pilot tone signal is received. This is advantageous for example when the pilot tone comprises a coded signal carrying additional information such as identification of the specific transmitter unit sending the signal.
If, in block 504, the pilot tone is detected then, in block 506 the controller 308 locks the radio receiver onto the channel via crystal oscillator 306. In block 508 the radio receiver demodulates the information signal and in block 510 the controller 308 changes the state of the muting control unit 309 to non-mute allowing the audio amplifier in block 512 to broadcast the audio signal via speaker 312. In block 516 the receiver unit monitors for loss of pilot tone which can occur, for example, because of low battery or power failure in the transmitter, physical separation of the unit in the pair beyond the transmitting range, strong interference from other transmitting units or electronic devices or a faulty transmitter device. If the pilot tone is lost then the receiver unit repeats the scanning process described above.
In one optimization corresponding to a simple transmitter unit configuration of the type discussed above with a constant pilot tone and information signal modulated onto a carrier frequency channel, the receiver unit similarly monitors for a simple pilot tone on any channel and only scans when the pilot tone is lost.
The presence of the pilot tone acts to trigger automatic adoption of the channel on which it is being carried at the receiving unit. There is no need for the receiving unit to confirm its identity or its detection of the pilot tone before it demodulates and broadcasts the audio signal via speaker 31. Because the pilot tone is modulated onto the transmission channel signal onto which the information signal channel is also modulated, the pilot tone serves both to identify the correct channel for the radio receiver to initially lock on to and to continuously indicate to the receiving unit whether the transmission channel onto which it is currently locked is the correct one. The continuous presence of the pilot tone signal on the channel on which the information signal is being transmitted removes the need for any further verification processes between the transmitter and receiver units during operation of the child monitoring system.
It will be appreciated that in addition to child monitor systems in which an audio signal is carried between transmitter and receiver, alternative types of child monitoring systems may also be embraced. For example a proximity detector of a type described in international patent application number PCT/GB2004/001678 , commonly assigned herewith and incorporated herein by reference, may incorporate a channel tracking approach as described herein. In such proximity monitors, a transmitter child unit sends a signal to a receiver parent unit and the receiver parent unit generates an alarm if the signal is lost or drops below a predetermined threshold indicating that the child unit has passed out of range. Such a system can, once again, suffer from problems switching between multiple channels. It will be apparent to the skilled reader that the arrangement described above can be simply modified to accommodate a proximity monitoring system by changing the nature of the information signal generated.
It will be appreciated that the specific detail of electronic component implementation to construct the transmitter and receiver unit and to program in the logic is a matter of mere workshop modification. Any appropriate component can be incorporated to the various elements of the construction and the control logic can be imposed as appropriate. For example, the controller 308 may comprise a microprocessor for timing, power control and logical operation. The generation and modulation of the carrier signal and the selection of channels can again be according to any appropriate scheme. In one embodiment the channels span the band 49.82 to 49.98MHZand 5 channels are provided but it will be appreciated that any number of channels on any appropriate band can be adopted. Furthermore the scanning regime and the time taken to determine if a pilot tone is carried on an appropriate channel can be any appropriate scheme for example one scan per second.
It will further be appreciated that a pilot tone can be generated in any appropriate manner and either form a simple tone or complex coded tone which can be governed by appropriate circuitry or retrieved from memory as required. Any coding scheme can be adopted. Yet further the arrangement can be adopted in any multi-channel wireless transmission configuration such as RF and other frequency bands.
As a result of the arrangement described a range of advantages can be achieved. For example where the system works on an analog configuration, high quality transmission can be achieved. Alternatively where a digital scheme is adopted then the information can be carried together with further channels. In either case the arrangement provides reliability and clarity of sound, together with stable channel locking via PLL and automatic adoption of the appropriate channel at the receiver unit randomly selected on the transmitter unit in a time interval between one and ten seconds which is entirely acceptable in view of the implementations of the device. As a result the use of identifier signal pilot tones ensures that interference or lost signal is avoided satisfactorily.
It will be appreciated that features from the arrangements described above can be interchanged and juxtaposed as appropriate. Furthermore the method steps set out can be carried out in any appropriate order. For example it is quite possible that demodulation of the information signal and pilot tone of the receiving unit take place simultaneously. Similarly the modulation of the carrier frequency with both the pilot tone and the information signal can take place simultaneously. The system can be realized using a digital or analog architecture as appropriate. The system can be applied to any appropriate monitoring scheme for children of any age including infants and indeed for other monitoring applications for example for the elderly or less-abled. Although discussion is made of modulating the carrier pilot tone it will be recognized that any appropriate manner of carrying the pilot tone on the relevant channel can be adopted. Although a simple block diagram is provided for each of the transmitter and receiver unit it will be appreciated that the components shown can in fact provide multiple functions or can be further split up into sub components as appropriate.

Claims

A multi channel child monitor unit comprising a multi channel transmitter and an identifier signal generator in which the identifier signal generator is controllable to generate an identifier signal for triggering adoption by a receiver unit of a channel carrying said identifier signal and the multi channel transmitter is controllable to transmit on one of a plurality of transmission channels and to transmit said generated identifier signal on said transmission channel, wherein the identifier signal is modulated onto a transmission channel signal.
A unit as claimed in claim 1 manually switchable between transmission channels.
A unit as claimed in any preceding claim in which the identifier signal generator is arranged to generate a characteristic frequency pilot tone as identifier signal, or
in which the identifier signal generator is arranged to generate a coded sequence pilot tone as identifier signal.
A unit as claimed in any preceding claim further comprising an information signal generator in which the transmitter is arranged to transmit the information signal on the transmission channel.
The unit as claimed in claim 4 in which the information signal comprises an audio signal, or
in which the information signal comprises a proximity signal.
A multi channel child monitor unit comprising a multi channel receiver, an identifier signal detector and a controller, in which the controller is arranged to control the receiver to search for and lock onto a receiving channel on which an identifier signal is detected by the detector.
A unit as claimed in claim 6 in which the receiver is controllable to scan across multiple channels to detect an identifier signal.
A unit as claimed in claim 6 or claim 7 in which the identifier signal detector is arranged to decode the identifier signal.
A unit as claimed in any of claims 6 to 8 in which the receiver is further controllable to extract an information signal from a received signal.
A unit as claimed in claim 9 of which the information signal comprises an audio signal, or
in which the information signal comprises a proximity signal.
A unit as claimed in any of claims 6 to 10 in which the receiver is further controllable to monitor for the loss of the identifier signal, and preferably
in which the controller is arranged to control the receiver to search for and lock onto a receiving channel on which the identifier signal is detected upon loss of the identifier signal.
A unit as claimed in any of claims 6 to 11 further comprising a mute unit arranged to mute an information signal until an identifier signal is detected.
A multi channel child monitor system comprising a unit as claimed in claim 1 and a unit as claimed in claim 6, and preferably
further comprising a unit as claimed in any one of claims 2 to 6 and/or 7 to 12.
A method of identifying a transmission channel in a multi channel child monitoring system comprising the steps, performed at a transmitter unit, of generating an identifier signal for triggering adoption by a receiver unit of a channel carrying said identifier signal, selecting one of a plurality of transmission channels, modulating the identifier signal onto a transmission channel signal, and transmitting the identifier signal on the transmission channel.
A method as claimed in claim 14 further comprising transmitting an information signal on the transmission channel.
A method of identifying a receiving channel in a multi channel child monitor system comprising searching a plurality of receiving channels and locking onto a receiving channel on which an identifier signal is received.
A method as claimed in claim 16 further comprising extracting an information signal from the received signal, and preferably
further comprising broadcasting the information signal upon identification of the identifier signal.
A processor configured to implement a method as claimed in any of claims 14 to 17.