Abstract:
A wireless intercom having a microcontroller that is programmed to place the intercom into a power saving sleep mode unless actively receiving or transmitting signals. The microcontroller of the intercom is interconnected to a transceiver for sending and receiving digital data packets, and to a codec for converting the digital packets to analog sound signals, and vice versa. The intercom receives digital transmission of data over a first channel and then corrects any errors in the digital data using a retransmission of the digital data over a second channel that is sufficiently spaced apart from the first channel to avoid the possibility of interference affecting both the first and second channels.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to intercoms and, more specifically, to a wirefree intercom having improved transmission quality. 
     2. Description of Prior Art 
     Conventional intercoms are powered by the wall outlet and transmit the voice of the speaker over the wires installed throughout the home. These intercoms use power line modulation techniques and have limited ranges due to the need for physical attachment to the power lines in the wall, as well as when the possibility of phase changes in the power connection that may interfere with the signal. In addition, the sound quality is often limited in such systems, and when there is a motor (such a hair dryer or vacuum cleaner) also in operation on the circuit, the signal is often distorted or destroyed. 
     Wireless intercoms use a radio signal and, like conventional intercoms, are powered by a wall outlet. These devices usually employ Family Radio Service (FRS) radio technology and have decent range capabilities. However, such devices do not provide security when multiple devices are employed in a dwelling. For example, if there are five units in a home and all are set to the same security number, each unit allows for reception of a conversation occurring between any other two units. In a business environment, this loss of security is not desirable. Additionally, such devices consume too much power and are thus not feasibly implemented without a direct power connection to a wall outlet. Some wireless intercoms use both wall power and batteries. In addition to limitation described above with respect to wireless intercoms, the batteries in such systems will only last about a day or two when the device is left on. 
     SUMMARY OF THE INVENTION 
     It is a principal object and advantage of the present invention to provide a wirefree intercom system that avoids the need for line power. 
     It is another object and advantage of the present invention to provide a wirefree intercom system that has low power consumption. 
     It is an additional object and advantage of the present invention to provide a wirefree intercom system having an unlimited number of units. 
     It is a further object and advantage of the present invention to provide a wirefree intercom system that provides secure conversation. 
     It is another object and advantage of the present invention to provide a wirefree intercom that is not affected by line noise. 
     It is an additional object and advantage of the present invention to provide a wirefree intercom system that has a long range. 
     It is a further object and advantage of the present invention to provide a wirefree intercom system that has clear sound qualities. 
     Other objects and advantages of the present invention will in part be obvious, and in part appear hereinafter. 
     In accordance with the foregoing objects and advantages, the present invention comprises wirefree intercom having circuitry and control processing that significantly reduces power consumption. More particularly, the intercom comprises a base unit and an antenna attached thereto for communicating with any number of other based units. Each base unit comprises a microcontroller, transceiver, codec, and speaker for receiving digital signal packets and converting into audible sounds and a microphone associated with the codec, microcontroller, and transceiver for converting sounds into digital data packets and transmitting to a remote intercom. The power reduction circuitry comprises the use of a wake timer and a talk timer that limit the amount of time that the associated circuitry remains operative. More particularly, the wake timer places the microcontroller in a timed, periodic sleep mode. After the expiration of the wake timer, the microcontroller activates the transceiver and checks for the presence of appropriate digital signals. If no signals are received, the intercom returns to sleep mode, thereby reducing power consumption. The intercom is programmed to receive digital transmission of data over a first channel and then corrects any errors in the digital data using a retransmission of the digital data over a second channel that is sufficiently spaced apart from the first channel to avoid the possibility of interference affecting both the first and second channels 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which: 
         FIG. 1A  is a perspective view of a wirefree intercom base unit according to the present invention. 
         FIG. 1B  is a perspective view of a wirefree intercom base unit according to the present invention. 
         FIG. 2  is a schematic of circuitry for a wirefree intercom base unit according to the present invention. 
         FIG. 3  is a flowchart of a control process for a wirefree intercom base unit according to the present invention. 
         FIG. 4  is a continuation of the flowchart of  FIG. 3  of a control process for a wirefree intercom base unit according to the present invention. 
         FIG. 5  is a flowchart of a pairing process for a wirefree intercom base unit according to the present invention. 
         FIG. 6  is a flowchart of a security process for a wirefree intercom base unit according to the present invention. 
         FIG. 7  is a flowchart of a power conservation process for a wirefree intercom base unit according to the present invention. 
         FIGS. 8A and 8B  are schematics of interference in a dual channel system according to the present invention. 
         FIG. 9  is flowchart of a digital signal restoration process for a wirefree intercom base unit according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, wherein like numerals refer to like parts throughout, there is seen in  FIGS. 1  A and  1 B a wirefree intercom  10  according to the present invention. Intercom  10  comprises a base unit  12  and an antenna  14  attached thereto. Base unit  12  houses the circuitry for providing wireless intercom capabilities, without the need for line power or excessive battery power usage, as will be described hereinafter. Base unit  12  further houses a power source, such as a conventional battery  13 , which may be received in a compartment  15  formed into the bottom of base unit  12 . Base unit  12  may further include a channel select button  16 , which allows a user to cycle through the preselected channels or select all of the preselected channels for transmission and reception. Intercom  10  may further comprise any number of illuminating regions  17  and  110 , such as LEDs, for reflecting the current operating mode of base unit  12 , such as “sleep” or active, for indicating whether the power “on,” etc. Intercom  10  further comprises a talk button  18  for transmitting from intercom  10 , a microphone  20  for receiving sounds to be transmitted, and a volume button  21  to control the volume of sounds played back on intercom  10 . 
     Referring to  FIG. 2 , base unit  12  comprises a microcontroller  22  interconnected to a codec  24  for converting analog signals to digital signals (and vice versa) and interconnected to a digital radio transceiver  26  for transmitting and receiving digital signals. Microcontroller  22  is selected to be able to perform radio base-band functions, carry out compression and de-compression of digitized data, assemble digital data transmission signals, and disassemble received digital data signals. As will be explained in detail hereinafter, microcontroller  22  further includes a wake timer  28  and a talk timer  30  for controlling whether and when base unit  12  is in “sleep” mode, thereby conserving energy, or a “wake” mode, where microcontroller  22  periodically “sniffs” for incoming signals. It should be recognized that wake timer  28  and talk timer  30  may be implemented in separate hardware devices or by programming wake timer  28  and a talk timer  30  into microcontroller  22 . Preferably, wake timer  28  of microcontroller  22  (and any other timers) comprises a watchdog style timer that may be operated while microcontroller  22  has otherwise been deactivated. Microcontroller  22  may comprise a low-power CMOS 8-bit microcontroller based on the AVR enhanced RISC architecture, such as an ATMEL Mega 88 available from the Atmel Corporation of San Jose, Calif. 
     Transceiver  26  is a conventional 915 MHz, multi-spectrum transceiver that is further associated with antenna  14  for transmitting and receiving digital radio signals. Transceiver  26  preferably supports about 125 radio channels, which may be chosen automatically or at the request of microcontroller  22 , and wherein each channel allows for communications without interfering with other channels. Transceiver  26  should be capable of reliably transmitting to and from another intercom  10  at distances of up to 1000 feet. Transceiver  26  may comprise a low power, low-IF transceiver designed for operation in the license-free ISM bands at 433 MHz, 868 MHz and 915 MHz, such as an ADF 7020 available from Analog Devices, Inc. of Norwood, Mass. 
     Codec  24  is a conventional encoder-decoder for converting analog signals to digital code, and vice versa. Codec  24  may further compress the signals to conserve bandwidth. Codec  24  may comprise an ultra low-power codec including a microphone supply, preamplifier, 16-bit ADC, 16-bit DAC, serial audio interface, as well as power management and clock management for the ADC and the DAC. The sampling frequency of the ADC and of the DAC is preferably adjustable 4 kHz to 48 kHz. For example, codec  24  may comprise an XE3005 available from Semtech Corporation of Camarillo, Calif. 
     The analog to digital input portion of codec  24  is interconnected to a microphone  32  for receiving voice signals and creating electrical analog voice signals from captured sounds. Codec  24  encodes the analog voice signals into digital packets and provides the encoded digital packets to microcontroller  22 . Microcontroller  22  buffers the digitized sound packets and applies compression algorithms, such as Adaptive Differential Pulse Code Modulation (ADPCM) or Delta Modulation, if desired, to reduce the packet size. An identification tag is also added to the packets, and they are sent by microcontroller to transceiver  26  for transmission to another base unit  12 . 
     The digital to analog portion of codec  24  is interconnected to a filter  34  for conditioning outgoing analog signals and reducing noise. Filter  34  may comprise an operational amplifier and conventional low pass, high pass, or band pass filter. 
     Filter  34  is further interconnected to an amplifier  36  for improving the quality of signals in the sound spectrum at the lowest possible power consumption. Microcontroller  22  may be interconnected directly to amplifier  36  for supplying control signals that control the power consumption of amplifier  36 . Amplifier  36  may comprise a conventional, off-the-shelf amplifier. 
     Amplifier  36  is connected to a speaker  38  for outputting audible sounds based on the amplified sound signals converted by codec  24  and processed by filter  34 . 
     Packets of data containing digitized voice signals, as well as an appropriate ID information data string, that are received by transceiver of base unit  12  are transferred from transceiver  26  to microcontroller  22  for playback. Microcontroller  22  decompresses the data (if necessary) and sends the signals to codec  24 . Codec  24  then converts the digital signals to analog sound signals, which are filtered by filter  34 , amplified by amplifier  36 , and output by speaker  38 . 
     The present invention reduces power consumption by engaging in a nearly complete shutdown of all circuitry for a predetermined period of time, which may be variable, depending on usage of intercom  10 . Referring to  FIG. 3 , the basic power-saving “sniff” process  40  of the present invention commences with the setting  42  of wake timer  28 , thereby placing intercom  10  in sleep mode. As a result, power consumption for unit  12  is reduced to the microamp range. When wake timer  28  expires  44 , microcontroller  22  awakes from sleep mode  46 , and “sniffs” for a signal by activating transceiver  26  for the receipt of signals  48 . A check is then performed  50  to determine whether any information received by transceiver  26  is discernable. If so, the incoming ID byte is checked  52  against a reference database  54  to determine whether it matches a stored ID. If not, base unit  12  goes back to sleep at step  42 , thereby conserving energy. If the ID matches, then microcontroller  22  awakens codec  24 , and enters full function mode, as illustrated in  FIG. 4 . 
     Referring to  FIG. 4 , if an ID is matched at step  52 , playback of data is enabled  56 . More specifically, codec  24  is enabled thereby starting packet reception, packet decompression, and error correction. Talk timer  30  is started  58 , and a check is performed  60  to determine whether packet reception has finished. If not, control returns to step  56 . If packet reception has finished at step  60 , a check is performed to determine whether talk button  18  has been depressed  62 . If talk button  18  has not been depressed, talk timer  30  is checked  64 . If talk timer  30  has expired, wake timer  28  is set  66  and intercom  10  is sent into sleep mode  68 . If talk timer  30  has not expired, control returns to step  50 . If the talk button was depressed at step  62 , talk timer  30  is extended  70  and a command byte is sent out  72  by transceiver  26  (to another intercom  10 ) to reverse the direction of communication. Transmission of data by intercom  10  is then enabled  74 . More particularly, microcontroller  22  switches transceiver  26  from receive mode to send mode, sound is collected by microphone  32 , and the resulting analog signals are converted by codec  24  into packet data. Microcontroller  22  compresses the packets, if desired, adds the appropriate ID, and assembles the data stream for transmission by transceiver  26  to another intercom  10 . 
     Intercom  10  may further be provided with a “pair” button  76  for commencing a pairing process  78  by which two or more intercoms  10  are configured for transmission therebetween. Referring to  FIG. 5 , pairing of a first intercom  10  with a second intercom  10  (or any number of additional intercoms  10 ) may be accomplished through pairing process  78  programmed into each intercom  10 . When a user wishes to pair two or more intercoms, the user presses  80  pair button  78  of first intercom  10 . The user then depresses  82  pair button  78  of any additional intercoms  10 . When pair button  78  is pressed, first intercom  10  checks internal memory  84  to determine whether an ID has been previously stored. If no ID has been previously stored  84 , receiver  26  of first intercom  10  listens for a predetermined period of time  86 , such as one second, and checks  88  to determine whether an ID has been received (from another intercom  10 ). If no ID is received from another intercom  10  at step  88 , first intercom generates a random ID  90  and begins transmitting the ID  92  for a predetermined amount of time. Intercom  10  may optionally decrease its RF output level by 30 dbm, so that the “teach” range is reduced to the immediate area. Intercom  10  then stored the ID  94  and sounds a successful pair  96 . If an ID has been sent by another intercom  10  and received at step  88 , first intercom  10  stores the ID in non-volatile memory  94  and generates a success tone from speaker  96 . After depressing pair button  76  of second intercom  10  at step  84 , second intercom cycles through the same process  78  as first intercom, and checks whether an ID is stored in memory  98 . If first intercom  10  has an ID stored in memory at step  84  and second intercom  10  does not, the ID of first intercom  10  is transmitted  100  to second intercom  10 , which will be listening for a predetermined time  102 . If first intercom  10  did not have an ID stored at step  84 , any stored ID in second intercom  10  will be transmitted to first intercom  10  and received at step  88 . If neither first nor second intercom  10  has an ID stored, the ID that is generated by first intercom  10  at step  90  and transmitted at step  92  will be received by second intercom  10  at step  102 , checked by second intercom  10  at step, stored in memory  106 , and a successful pair will be sounded  108 . 
     The present invention further provides for multiple, secure conversations occurring simultaneously on intercom  10 . As explained above, transceiver  26  supports multiple channels e.g., 125 channels. Preferably, a limited number, such as four, are dedicated for transmissions on intercom  10 , which may be indicated by a series of LEDS  110  on intercom  10 . Intercom  10  may further be configured to allow a user to select the specific channel to be used at all times, and may additionally be configured so that a user may choose to receive transmissions on “all channels” so that intercom  10  will receive and playback transmissions on any of the designated channels. Visual indication of the status may be reflected by cycling through four LEDs  110  as button  16  is depressed, to indicate transmissions on each of four particular channels for example, or lighting all LEDs when all channels have been selected. When a call is transmitted from an originating intercom  10 , the sound is played back on all intercoms  10  set to receive the designated channel (or set to receive “all channels”) and which have previously been “paired” to the originating intercom, i.e., the stored ID in all receiving intercoms  10  matches the ID of originating intercom  10 . 
     Referring to  FIG. 6 , a security protocol process  112  for engaging in secure transmissions may begin when a transmission on a designated channel from a first intercom  10  is initially received  114  by a second intercom  10  (or any additional intercoms  10 ). The second intercom then checks  116  to determine whether it is set to playback the channel of the first intercom  10 . If not, playback is inhibited  118 . If the channel is confirmed at step  116 , first and second intercoms select one of the non-designated channels  120  of transceiver  26 . For example, first and second intercoms  10  may using the last three digits of the ID of first and second intercoms  10  to select one or more of the unused 125 channels. Selection of multiple channels allows first and second intercoms  10  to have a back-up channel in case of interference on the initially selected channel. Alternatively, first and second intercoms  10  may use other means to select an unused channel or channels, such as a random channel selection. Selection  120  concludes with first and second intercoms  10  exchanging the channel or channel set, and first and second intercoms  10  then move transmission to the selected channel or channels  122 . The transmission may then be played back  124  on second intercom  10 . A user of second intercom  10  may then depress talk button  18  to respond the initial transmission  126 . A timer may started  128  (and reset) each time the user of second intercom  10  depresses talk button  18 , and then checked for expiration  130  so that first and second intercoms are reset to the designated, non-secure channel or channels  132 , as soon as transmissions conclude. Security process  112  allow other intercoms  10  to freely communicate on the designated channels without interfering with communications ongoing between first and second intercoms  10  on the secure channel or channels. Security process  112  may be provided as a default setting, and first and second intercoms  10  may be provided with a bypass switch  134  that allows a user to bypass security process  112  and remain in non-secure mode so that any other “paired” intercom  10  may playback the conversation. As two or more communicating intercoms  10  also provide the IDs created during pairing process  78  when they communicate, it is also possible that multiple set of intercoms  10 , each set having a different ID, may communicate securely on a given channel with respect to any intercom  10  not programmed to playback communications including that ID even if set to receive signal on the given channel. 
     Referring to  FIG. 7 , microcontroller  22  may implement a multi-stage, power-saving sleep mode process  136 , thereby substantially reducing power demand. In a first stage  138 , intercom  10  is actively engaged in a connection, i.e., all components are enabled, intercom  10  is connected to another intercom  10 , or intercom  10  is actively transmitting and receiving signals. A check is performed periodically  140  to verify that intercom  10  is active. If intercom  10  is inactive, intercom  10  is placed into a second, partial sleep stage where all unneeded components are disabled  142 . For example, amplifier  36  and LEDs  110  may be powered down to conserve energy. However, transceiver  26  is kept on to verify whether other intercoms have also terminated the connection. In addition, a sleep timer is started to measure a first sleep period  144  that controls how long intercom  10  is in stage two  142 . For example, sleep timer may be set for one hour. A check is then performed  146  to determine whether there is any system activity. If so, control returns to step  138 . If no activity is detected, the sleep timer is checked for expiration  148 . If the sleep timer has expired, intercom  10  enters a third sleep stage  150  where power is turned off to all components and wake timer  28  is set to measure a second time period  152 . Wake timer  28  is preferably set for 500 milliseconds. The sleep timer is also started  154  to measure a second sleep period. Power saving process  136  then follows the basic “sniff” process, as illustrated in  FIG. 3 , every 500 milliseconds, i.e., a check is performed  156  to determine whether a signal of interest has been received. If no signal are detected at step  156 , sleep timer is checked  158  to determine whether intercom  10  has been in third stage  150  for more than a predetermined time, such as four hours. If so, intercom  10  enters a final sleep stage  160 , where all components are turned off and wake timer  28  is set  162  for a longer period of time that at step  152 , such as two seconds. As illustrated in  FIG. 3 , microcontroller  22  executes the “sniff” process of  FIG. 3  every two seconds, thereby further reducing power consumption while intercom  10  is in third stage  150 . It should be recognized that multi-stage, power-saving sleep mode process  136  may be implemented in any digital transmitting and receiving device having a transceiver and microcontroller where reduced power consumption is advantageous. For example, process  136  could be implemented in a wireless security access system and even a wireless headset for a cellular or conventional telephone. 
     Microcontroller  22  may be programmed to improve the quality of analog playback from digitally transmitted signals. Interference may be reduced or eliminated by transmitting data transmitting data over a first channel and then immediately transmitting the data over a second, different channel, regardless of whether the receiving intercom request missing data. The second transmission may be used to repair or reconstruct any data lost or damaged in the first transmission. The first and second channels should be selected to reduce the likelihood that any interference in the transmission band of transceiver  26  will affect both channels. As seen in  FIG. 8A , first channel  164  is selected to be above the minimum frequency  166  of transceiver  26 , and a predetermined distance from second channel  168 , which is less than the maximum frequency  170  of transceiver  26 . In  FIG. 8A , interference  172  is not affecting transmissions on either first channel  164  or second channel  166 . In  FIG. 8B , interference  172  is on or near second channel  166 . First channel  164  is free from interference  172 . Accordingly, any lost data in digital transmissions over second channel  166  could be repaired by the transmissions occurring over on first channel  164 . 
     Microcontroller  22  may thus implement a sound quality improvement process  174  for increasing the clarity of transmissions between two or more paired intercoms  10 . Transmission improvement process  174  commences with a valid transmission between two intercoms  176 . Intercoms  10  then select the two channels for data transmission  178  (and the channel selection results are shared between intercoms  10 ). The first and second channels may chosen in advance by microcontroller  22  using a lookup table  180  containing a list of pairs of channel numbers. Microcontroller  22  may automatically select the channel pair, or the channel pairs may be factory installed and selected by a dipswitch. Automatic selection of the channel pair can be achieved by generating a random number in microcontroller  22  and then using the number to select the channel pair from look-up table  166 . Alternatively, the channel pair could be selected by using the security ID generated or stored by intercom  10  to select a channel set. Table 1 below contains a list of 10 sets of channel pairs that may be selected by microcontroller  22  in the 902-937 Mhz band, with 3 Mhz channel spacing. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Channel Set No. 
                 1 st  channel 
                 2 nd  channel 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 902 
                 910 
               
               
                 2 
                 905 
                 913 
               
               
                 3 
                 908 
                 916 
               
               
                 4 
                 911 
                 919 
               
               
                 5 
                 914 
                 922 
               
               
                 6 
                 917 
                 925 
               
               
                 7 
                 920 
                 928 
               
               
                 8 
                 923 
                 931 
               
               
                 9 
                 926 
                 934 
               
               
                 10 
                 929 
                 937 
               
               
                   
               
             
          
         
       
     
     With reference to  FIG. 9 , once the channels are selected and shared  178 , transceivers  26  of intercoms  10  are set  182  to transmit and receive on the designated channel set. When data is received over the first channel  184 , microcontroller  22  checks the data integrity  186 . If data is good at step  186 , more data may be received at step  184 . If the data is damaged, transceiver  26  is set to the second channel  188  so that intercom  10  may receive the redundant transmission of data sent over the second channel  190 . The missing or damaged data packets received in the first transmission at step  184  are then extracted  192  from the data received in the second transmission over second channel at step  190 . The extracted packets are then assembled  194  with the data received at step  184  to form an error data stream. Transceiver  26  is reset back to the first channel  196  (so that more data may be received at step  184 ), and the repaired data from step  194  is played back  198  by the receiving intercom  10 . In this manner, the sound quality of transmitted signals is improved by repairing or replacing data that would have been otherwise lost in transmission. It should be recognized that sound quality improvement process  174  may be implemented in any digital transmitting and receiving device having a digital transceiver and associated microcontroller where reduced power consumption is advantageous. For example, process  174  could be implemented in a wireless security access system, a digital walkie-talkie system, or even in a wireless headset for a cellular or conventional telephone.