Classifications

• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B21/00—Alarms responsive to a single specified undesired or abnormal condition and not otherwise provided for
  • G08B21/02—Alarms for ensuring the safety of persons
  • G08B21/0202—Child monitoring systems using a transmitter-receiver system carried by the parent and the child
  • G08B21/0205—Specific application combined with child monitoring using a transmitter-receiver system
  • G08B21/0208—Combination with audio or video communication, e.g. combination with "baby phone" function

Definitions

• the invention relates to a multi channel child monitor and method.
• 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.
• RF radio frequency
• 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.
• Figure 1 is a schematic diagram of a transmitter-receiver pair in a child monitor system
• FIG. 2 is block diagram showing the components of a transmitter unit according to the invention
• FIG. 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;
• Figure 5 is a flow diagram showing the steps followed in the receiver unit.
• 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.
• the pilot tone is imposed on the new channel.
• an identifier signal detector scans all of the channels to detect the pilot tone and locks onto the channel carrying the pilot tone.
• the receiver unit automatically tracks any changes in channel triggered at the transmitter unit such that it is not necessary to switch both units.
• 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.
• 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.
• PLL phase locked loop
• 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.
• the logic controller is further associated with a data storage means 314 storing identifier signal data.
• FIG. 4 shows the steps performed at a transmitter unit.
• 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.
• 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.
• 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.
• 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.
• pilot tone can be the same for all channels in which case a simple tone generator can be adopted.
• 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.
• 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.
• 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.
• 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.
• 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.
• the radio receiver 304 selects a first channel under the control of controller 308 and crystal oscillator 306.
• the received signal is filtered, demodulated or otherwise processed as appropriate to detect whether any pilot tone is received.
• 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.
• 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.
• the pilot tone comprises a coded signal carrying additional information such as identification of the specific transmitter unit sending the signal.
• the controller 308 locks the radio receiver onto the channel via crystal oscillator 306.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.

Landscapes

• Child & Adolescent Psychology (AREA)
• General Health & Medical Sciences (AREA)
• Health & Medical Sciences (AREA)
• Emergency Management (AREA)
• Multimedia (AREA)
• Business, Economics & Management (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Alarm Systems (AREA)
• Transmitters (AREA)
• Monitoring And Testing Of Transmission In General (AREA)
• Circuits Of Receivers In General (AREA)
• Time-Division Multiplex Systems (AREA)
• Testing, Inspecting, Measuring Of Stereoscopic Televisions And Televisions (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=34508933

Family Applications (1)

Country Status (7)

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Family Cites Families (3)

• 2005
  • 2005-03-11 GB GBGB0505069.5A patent/GB0505069D0/en not_active Ceased
• 2006
  • 2006-03-06 WO PCT/GB2006/000788 patent/WO2006095152A1/fr not_active Application Discontinuation
  • 2006-03-06 AU AU2006221847A patent/AU2006221847A1/en not_active Abandoned
  • 2006-03-06 AT AT06710008T patent/ATE411582T1/de not_active IP Right Cessation
  • 2006-03-06 CA CA002599527A patent/CA2599527A1/fr not_active Abandoned
  • 2006-03-06 DE DE602006003195T patent/DE602006003195D1/de not_active Expired - Fee Related
  • 2006-03-06 EP EP06710008A patent/EP1859421B1/fr not_active Not-in-force

Non-Patent Citations (1)

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