Abstrict
A baby monitor has a nursery unit and parent unit. The nursery
unit has a controller for generating a privacy code, a microphone
for detecting baby sounds and a transmitter for transmitting a signal
made up of the privacy code and the baby sounds. The parent unit
has a receiver for receiving the signal, a controller for comparing
the privacy code to a reference code, and an amplifier and speaker
for outputting the baby sounds. The baby sounds are output by the
parent unit if the privacy code matches the reference code. The
nursery and parent units have a scrambler and descrambler respectively
for scrambling the signal.
Claims
What is claimed is:
1. A baby monitor including: a nursery unit having a controller
for generating a privacy code, a microphone for detecting baby sounds,
a scrambler for scrambling a signal including the privacy code and
the baby sounds, and a transmitter for transmitting the signal after
scrambling; and a parent unit having a receiver for receiving the
signal transmitted from the nursery unit, a descrambler for unscrambling
the signal to produce the privacy code and the baby sounds, a controller
for comparing the privacy code to a reference code, and an amplifier
and speaker for outputting the baby sounds, wherein the controller
supplies the baby sounds to the amplifier only if the privacy code
matches the reference code.
2. The baby monitor of claim 1 wherein the controller of the nursery
unit comprises a memory unit storing a code lookup table and a processor
for accessing the code lookup table for generating the privacy code.
3. The baby monitor of claim 1 wherein the controller of the parent
unit comprises a memory unit storing a code lookup table, the lookup
table including the reference code, and a processor for accessing
the code lookup table and comparing the privacy code to the reference
code.
4. The baby monitor of claim 1 wherein the scrambler includes a
modulator and filter.
5. The baby monitor of claim 4 wherein the modulator includes a
switch operating at a fixed frequency and an operational amplifier
in a difference amplifier configuration.
6. A baby monitor including: a nursery unit having a controller
for generating a privacy code, a microphone for detecting baby sounds,
a scrambler for scrambling a signal including the privacy code and
the baby sounds, and a transmitter for transmitting the signal;
and a parent unit having a receiver for receiving the signal transmitted
from the nursery unit, a descrambler for unscrambling the signal
to produce the privacy code and the baby sounds, a controller for
comparing the privacy code to a reference code, and an amplifier
and speaker for outputting the baby sounds, wherein the controller
supplies the baby sounds to the amplifier only if the privacy code
matches the reference code, wherein the scrambler includes a modulator
and a filter, the modulator includes a switch operating at a fixed
frequency and an operational amplifier in a difference amplifier
configuration, and the fixed frequency is given by f(c)-f(u)=f(l),
where f(c) is the fixed frequency, f(u) is a frequency spectrum
upper limits and f(l) is a frequency spectrum lower limit.
7. The baby monitor of claim 1 wherein the nursery unit further
includes means for signalling the parent unit and causing the parent
unit to output a sound from the speaker.
8. The baby monitor of claim 1 wherein the parent unit further
includes a visual indicator, and the nursery unit further includes
means for signalling the parent unit and causing the parent unit
to activate the visual indicator.
9. A method of scrambling/descrambling an audio signal in a baby
monitor, the audio signal comprising an alternating amplitude over
a frequency spectrum having an upper limit and a lower limit, the
method comprising transforming the audio signals to mirror the amplitude
within the frequency spectrum by generating a multiplier signal,
multiplying the audio signal and multiplier signal to produce a
resultant signal, and filtering the resultant signal to remove frequencies
above and below the upper and lower limits.
10. The method of claim 9 wherein the multiplier signal has a frequency
given by f(c)-f(u)=f(l), where f(c) is the multiplier signal frequency,
f(u) is the frequency spectrum upper limit and f(l) is the frequency
spectrum lower limit.
11. The method of claim 9 wherein the frequency spectrum upper
limit is 20000 Hz and the frequency spectrum lower limit is 15 Hz.
12. The method of claim 9 wherein multiplying the audio signal
and multiplier signal includes modulating the audio signal and multiplier
signal.
13. The baby monitor of claim 6 wherein the controller of the nursery
unit comprises a memory unit storing a code lookup table and a processor
for accessing the code lookup table for generating the privacy code.
14. The baby monitor of claim 6 wherein the controller of the parent
unit comprises a memory unit storing a code lookup table, the lookup
table including the reference code, and a processor for accessing
the code lookup table and comparing the privacy code to the reference
code.
15. The baby monitor of claim 6 wherein the nursery unit further
includes means for signalling the parent unit and causing the parent
unit to output a sound from the speaker.
16. The baby monitor of claim 6 wherein the parent unit further
includes a visual indicator, and the nursery unit further includes
means for signalling the parent unit and causing the parent unit
to activate the visual indicator.
Description BACKGROUND TO THE INVENTION
1. Field of the Invention
The invention relates to baby monitors.
2. Background Information
Baby monitors that allow remote monitoring of a baby are well-known.
The device typically includes a nursery unit which is place in a
room with a baby or infant who is either playing or sleeping, and
a parent unit which is located in another part of the house or building
where the parent or guardian is. The nursery unit detects sounds
made by the baby and transmits these sounds to the parent unit where
it is output via a speaker. The parent unit may also have one or
more visual indicators.
Privacy can be a problem with known baby monitors. If two families
living in neighbouring flats of the same apartment complex purchase
baby monitors of same frequency channels transmitted signals may
be received by the parent unit in the neighbouring apartment. A
parent or guardian may hear their own baby as well as the neighbouring
baby sounds.
Security can also be a problem with known baby monitors. The baby
monitors transmit audio signals at frequencies that can be received
by other baby monitors and by commonly available radio receivers.
It is therefore relatively easy for others to `eavesdrop` on audio
signals transmitted by baby monitors. This could pose a security
problem if sensitive or confidential information is discussed while
a baby monitor is `listening`.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a baby monitor
which overcomes or ameliorates the above mentioned problems.
According to a first aspect of the invention there is provided
a baby monitor including: a nursery unit having a controller for
generating a privacy code, a microphone for detecting baby sounds
and a transmitter for transmitting a signal, the signal comprising
the privacy code and the baby sounds, and a parent unit having a
receiver for receiving the signal, a controller for comparing the
privacy code to a reference code, and an amplifier and speaker for
outputting the baby sounds, wherein the baby sounds are output only
if the privacy code matches the reference code.
Preferably, the nursery unit further includes a scrambler for scrambling
the signal, and the parent unit further includes a descrambler for
unscrambling the signal.
Preferably, the nursery unit controller comprises a memory unit
storing a code lookup table and a processor for accessing the code
lookup table for generating the privacy code.
Preferably, the parent unit controller comprises a memory unit
storing a code lookup table, the lookup table including the reference
code, and a processor for accessing the code lookup table and comparing
the privacy code to the reference code.
Preferably, the scrambler and descrambler include a modulator and
filter.
Preferably, the modulator includes a switch operating at a fixed
frequency and an operational amplifier in a difference amplifier
configuration.
Preferably, the fixed frequency is given by f(c)-f(u)=f(l), where
f(c) is the fixed frequency, f(u) is a frequency spectrum upper
limit and f(l) is a frequency spectrum lower limit.
Preferably, the nursery unit further includes means for signalling
the parent unit and causing the parent unit to output a sound from
the speaker and/or providing a visual indication.
According to a second aspect of the invention there is provided
a method of scrambling/descrambling an audio signal in a baby monitor,
the audio signal comprising an alternating amplitude over a frequency
spectrum having an upper limit and a lower limit, the method comprising
transforming the audio signal so as to mirror the amplitude within
the frequency spectrum.
Preferably, transforming the signal comprises: generating a multiplier
signal, multiplying the audio signal and multiplier signal to give
a resultant signal, and filtering the resultant signal to remove
frequencies above and below the upper and lower limits.
Preferably, the multiplier signal has a frequency given by f(c)-f(u)=f(l),
where f(c) is the multiplier signal frequency, f(u) is the frequency
spectrum upper limit and f(l) is the frequency spectrum lower limit.
Preferably, the frequency spectrum upper limit is 20000 Hz and
the frequency spectrum lower limit is 15 Hz.
Preferably, multiplying the audio signal and multiplier signal
includes modulating the audio signal and multiplier signal.
Further aspects of the invention will become apparent from the
following description, which is given by way of example only.
BRIEF DESCRIPTION OF THE DRAWINGS
An embodiment of the invention will now be described by way of
example only and with reference to the accompanying drawing, in
which:
FIG. 1 is a schematic diagram of a first nursery unit for a baby
monitor,
FIG. 2 is a schematic of a first parent unit for a baby monitor
according to the invention,
FIG. 3 is a schematic of a second nursery unit for a baby monitor,
FIG. 4 is a schematic of a second parent unit for a baby monitor,
FIGS. 5 and 6 illustrate a system of scrambling an audio signal,
FIG. 7 illustrates a scrambler/descrambler,
FIG. 8 is a schematic of a two-way half-duplex transceiver,
FIG. 9 illustrates a three-way walkie-talkie system, and
FIG. 10 is a schematic of a controller for the nursery and parent
units.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1 and 2, a baby monitor includes a nursery unit
and one of more parent units. A nursery unit for locating in a nursery
with a baby to be monitored includes a microphone 1 for detecting
sounds, a microphone amplifier 2, a controller 3, a transmitter
4 and an antenna 5. The microphone 1 detects sounds made by the
baby. The sounds are amplified by the microphone amplifier 2 and
transmitted by transmitter 4 and antenna 3.
The parent units include an antenna 6, a receiver 7, a controller
8, an amplifier 9 and a loudspeaker 10. The antenna 6 and receiver
7 receive the transmitted signal from the nursery unit. The received
signal is amplified by the amplifier 9 for output over the loudspeaker
10. The nursery and parent units are controlled by controllers 3
and 8.
In one aspect of the invention the transmitted baby sounds are
preceded by a privacy code. If the code is not recognised by the
parent unit then the parent unit will not output the baby sounds
over the speaker. In the preferred embodiment the code is transmitted
as a digital signal followed by the analogue baby sound. To avoid
the possibility that the privacy code used in one baby monitor coincides
with the code used in another nearby baby monitor the privacy code
is a randomly generated by the nursery unit controller 3 when it
is turned on. Because a randomly generated code is used, the nursery
unit and parent unit must undergo code registration before normal
operation.
Referring to FIG. 10, the controllers 3, 8 each comprise a microcontroller
17 and Read Only Memory (ROM) 18 for storing a pre-set code table.
When the nursery unit is turned on its controller 3 generates a
digital code randomly chosen from the code table. When the parent
unit is turned on it communicates with the nursery unit to obtain
the generated digital code and compares the code with its own pre-set
code table for verification. If the digital code is verifiable as
a valid code it is stored in microcontroller 17 memory as the reference
identity for the nursery unit. After the parent unit has registered
the valid code it generates a sound or uses a visual indicator light
to indicate that code registration with the nursery unit was successful.
If the parent or guardian wishes to have more than one parent unit
operating, for separate rooms, they turn on the second parent unit
after receiving confirmation of successful code registration from
the first parent unit. The second parent unit then undergoes the
same code registration procedure of communicating with the nursery
unit to obtain the digital code, verifying it, and storing in memory
as the identity of the nursery unit. Additional parent units may
be used and each is turned on, one-by-one, to undergo code registration
before the next unit is turn on.
In order to insure that a parent unit undergoes code registration
with the correct nursery unit, and not a nursery unit from a neighbouring
apartment, the registration must be completed within a fixed time
period, say 60 seconds, of the nursery unit being turned on. The
nursery unit is turned on and randomly generates the digital code.
For code registration to be successful the first parent unit must
be turned on within 60 seconds of the nursery unit. If the nursery
unit does not register a parent unit within 60 seconds of being
turned on it will not allow registration of a parent unit. This
prevents a person in the neighbouring flat turning on their parent
unit at a later time and the parent unit undergoing code registration
with the nursery unit from the neighbouring flat.
Once code registration is completed the nursery and parent units
go into normal operation mode. The parent unit has its output speaker
10 muted. The nursery unit is monitoring the input from its microphone
1. If the sound level received by the microphone 1 is above a pre-determined
threshold level the nursery unit will transmit the privacy code
and then the detected sounds. The parent unit receives the transmitted
code and sounds, and if the code matches the registered code the
parent unit un-mutes its speaker 10 function and plays the baby
sounds over the speaker 10. If the privacy code does not match the
registered code then the parent unit remains muted.
In an alternative embodiment, the code is fixed, i.e. not randomly
generated. The code is pre-set using hardwire jumpers connected
to the controller 3 and to the controller 8. Corresponding nursery
unit and parent unit are pre-set with the same code. Eight binary
jumper inputs can provide a selection of 256 different codes, which
means a 1-in-256 chance of coincidence of codes used by different
baby monitor units. In yet a further embodiment the preset code
is programmed into the ROMs 18 of the controller 3 and controller
8.
The nursery unit also has a parent-unit-finder function. Pressing
a switch on the nursery unit will make the registered parent units
provide audio and/or visual indication, which helps to locate them.
The nursery unit transmits the privacy code followed by an activation
code which is to enable the parent-unit-finder function. The preceding
privacy code is to identify the parent units with codes matched,
and any parent units unregistered or with codes mismatched would
not produce any corresponding indication.
In one embodiment the baby monitor also includes security features.
Referring to FIGS. 3 and 4, the nursery unit also includes a scrambler
11. The microphone 1 detects sounds made by the baby. The sounds
are amplified by the microphone amplifier 2. The amplified sounds
are scrambled by scrambler 11 and then transmitted by transmitter
4 and antenna 5. The parent unit includes a de-scrambler 27. The
antenna 6 and receiver 7 receive the transmitted signal from the
nursery unit. The received signal is de-scrambled by descrambler
12, amplified by amplifier 9 and output over loudspeaker 10.
The scrambler 11 and descrambler 12 may be a known scrambler IC.
However, scrambler ICs are expensive.
A low cost scrambler is provided by transforming the audio signal
amplitude to be mirror of itself within its frequency spectrum in
order to make sounds incomprehensible. This is illustrated by the
two graphs in the upper part of FIG. 5. The scrambled signal (right
graph) lies within the same frequency spectrum as the original signal
(left graph) and is a mirror image of the original signal in a graph
of signal amplitude (level) versus frequency. To unscramble the
signal the transformed signal is mirrored again in order to reveal
the original signal and make the sounds comprehensible. Therefore,
the scrambler is identical to the de-scrambler in terms of function
and structure.
Referring to FIG. 5, mirroring of the audio signal amplitude within
its frequency spectrum is achieved using a modulator 50 and a low
pass filter 51. The modulator 50 acts as an analogue multiplier
circuit. If two signals are multiplied the result is sum and difference
signals. Referring to FIG. 6, if the sound signal 61 is multiplied
by a carrier signal 63 the result is the carrier 63 and two sideband
signals 62, 64. The low pass filter 51 is used to remove the carrier
signal 63 and upper sideband 64 leaving the lower sideband 62 which
is a mirror of original sound signal 61 within the frequency spectrum.
The frequency (fc) of the carrier signal 63 must be chosen so that
the lower sideband 62 occupies the same frequency spectrum range
as the original sound signal 61. The upper sideband 64 occupies
the frequency range of fc+f(l) to fc+f(u) and the lower sideband
62 occupies the frequency range of fc-f(u) to fc-f(l): where f(l)
and f(u) are the lower and upper limits of the sound signal 61 frequency
spectrum respectively. In order to use the same modulator circuit
to unscramble the sound signal by re-mirroring the frequency spectrum
fc must be chosen such that fc-f(u)=f(l). For example, if the input
signals spectrum is from 300 Hz to 3000 Hz then fc-3000=300 and
so the carrier signal frequency fc=3300 Hz. The input signal frequency
spectrum can include the range of frequencies that can be detected
(heard) by the human ear. This is normally considered to be within
the range of 15 Hz to 20000 Hz.
FIG. 7 shows a circuit that can be used as both a scrambler 11
and de-scrambler 12. The circuit includes a modulator 50 having
an analogue switch 71 connected to an operational amplifier 72.
The analogue switch 71 can be any low cost commercially available
analogue switch quad package. The modulator 50 requires only one
of the four analogue switches. The remaining switches can be used
in other areas such as signal flow control which helps to reduce
the total cost of components. The operating frequency of the switch
71, which determines the carrier frequency, is determined by a frequency
input 74.
A variable resistor 73 is provided at the input. The variable resistor
73 is tuned to minimise the content of the carrier signal 63 in
the modulator output. If the carrier signal 63 content in the output
is high a more expensive low pass filter 51 with deep roll off is
required to remove the entire carrier signal 63. Because the variable
resistor 73 can be tuned to minimise the carrier signal 63 content
of the output the deep roll off low pass filter is not required,
minimising cost.
The spectrum of the modulator input (sound signal 61) occupies
exactly the same range of the frequency spectrum of the lower side
band 62 of the modulator output. There would be a superposition
or overlap problem if some of the frequency content of the sound
signal 61 remained un-mirrored. In order to reduce this problem
the feedback path of the amplifier 72 is provided with a variable
resistor 75 which can be tuned to minimise any un-mirrored content
in the modulator output.
A low pass filter 52 is provided before the modulator 50 to clean
the audio signal 61 so that no higher frequencies/noises are present.
FIG. 8 shows two-way half-duplex transceiver that can be used for
both a nursery unit and a parent unit. It comprises a transmitter
portion 15 and receiver portion 16 and a single scrambler/de-scrambler
circuit 13. A micro-controller 14 switches the circuit 13 between
scrambler and de-scrambler modes for processing the sound signals.
The nursery unit, which is located in a nursery with a baby to
be monitored, is always monitoring the baby sounds as in the case
described previously. If the sound level received by the microphone
1 is above a pre-determined threshold level the nursery unit will
transmit the privacy code and then the detected sounds. Whatever
the sound level, the receiver portion 16 of the nursery unit is
always active, detecting whether a parent unit is transmitting.
When the sound level received by microphone 1 is higher than the
threshold level, both the transmitter portion 15 and the receiver
portion 16 of the nursery unit are working, one at each frequency
channel.
The parent unit is usually in a "receive" mode, detecting
whether the nursery unit is transmitting. The parent unit is provided
with a transmit button (not shown) to switch it to "transmit"
mode. In transmit mode the parent unit transmits sounds produced
by the parent to the nursery unit.
The transmitted signal from the parent unit includes a privacy
code and privacy code checking as described previously is performed
both at nursery and parent units.
Because the transceiver unit of FIG. 8 has only one scrambler/de-scrambler
circuit 13 it can only operate in either transmit mode or receive
mode at one time. In normal operation mode, i.e. listening for baby
sounds, the scrambler/de-scrambler circuit 13 of the nursery unit
is set to scramble mode and the scrambler/de-scrambler circuit 13
of the parent unit is set to de-scramble mode. When the transmit
button of the parent unit is pressed its controller 14 switches
its scrambler/de-scrambler circuit 13 to scramble mode. A signal
is transmitted to the nursery unit. When the nursery unit controller
14 detects that it has received a signal containing the privacy
code it turns off the transmit function of the nursery unit and
switches the nursery unit scrambler/de-scrambler circuit to de-scramble
mode so that the received signal can be output on speaker 10. The
nursery unit reverts to normal operation mode if a received signal
containing the privacy code is absent for a pre-determined period
of time, say 2 seconds.
Referring to FIG. 9, two parent units 91, 93 of the transceiver
type shown in FIG. 8 are registered with a transceiver type nursery
unit 92. If the units are using randomly generated privacy codes
registration of two parent units proceeds as described previously.
Alternatively, if fixed privacy codes are used then no registration
is required. The three units can operate as a 3-way walkie-talkie
system. The nursery unit 92 serves as the central unit for all communications
between itself and either of the parent units 91, 93 or between
the two parent units 91, 93. Parent-to-parent communication is performed
via the nursery unit 92, and is an extra function over two-way communication
system.
If a parent at parent unit 91 wishes to communicate with the nursery
unit 92 a parent-to-baby button (not shown) is pressed on parent
unit 91 to establish communication between parent unit 91 and nursery
unit 92. When communication is established parent unit 91 will indicate
that the nursery unit 92 is ready by an audio beep, visual indicator
or similar.
Once communications have been established between a parent unit,
in this case unit 91, and the nursery unit 92 a second parent unit,
for example 93, will not be able to communicate with the nursery
unit 92. If second parent unit 93 tries to establish communication
with the nursery unit 92 then its signal will be rejected and a
busy tone generated at second parent unit 93.
The nursery unit 92 may also act as a central link between parent
units 91 and 93.
The privacy code checking described in nursery-to-parent simplex
and two-way communication systems is also applied to the 3-way system.
In addition, there is an identity code for each parent unit so that
the nursery unit 92 can identify them accordingly, in order to establish
communication from parent unit 91 to parent unit 93 or vice versa.
The identity code is an extra code following the privacy code.
Alternatively, two different privacy codes are used for parent units
91 and 93 so the nursery unit identifies them by privacy code.
If a parent-to-parent button (not shown) is pressed on parent unit
91 then nursery unit 92 tells second parent unit 93 to enter receive
mode only, by disabling its transmit mode. The speaker is muted
on nursery unit 92 and communication signals are routed from parent
unit 91 to second parent unit 93. Communication from parent unit
93 to parent unit 91 can be established in similar manner.
If both the parent-to-baby and parent-to-parent buttons are pressed
on parent unit 91 then nursery unit 92 tells parent unit 93 to enter
receive mode only, by disabling its transmit mode. The speaker is
not muted on nursery unit 92, though communication signals are routed
to parent unit 93. Both nursery unit and parent unit 93 can hear
the sound signals from parent unit 91. Communication from parent
unit 93 to nursery unit 92 and parent unit 91 can be established
in similar manner.
Where in the foregoing description reference has been made to integers
or elements have known equivalents then such are included as if
individually set forth herein.
Embodiments of the invention having been described, however it
is understood that variations, improvements or modifications can
take place without departure from the spirit of the invention or
scope of the appended claims. |