Abstract:
A system detects an incoming telephone call and routes the ring signal to a loudspeaker so that it can be heard at a distance from the telephony device. Once the incoming call has been acknowledged the incoming signal is routed to the headset. New incoming calls are identified by verifying the presence of unique characteristics that are found only in incoming calls. In a conventional telephone the unique characteristic can be a combination of frequencies which are part of the ring signal. The frequencies can be verified by using a bandpass filter which allows only frequencies centered around the ring frequency to pass. Therefore, if a signal of correct frequency is present it will pass through the bandpass filter and activate a switch that routes the signal to the loudspeaker.

Description:
This application claims the priority of U.S. Provisional No. 60/180,382 filed on Feb. 4, 2000. 

   FIELD OF THE INVENTION 
   This invention relates generally to telephone systems, and more particularly to signaling incoming calls to recipients who otherwise may have difficulty hearing a telephone ring. 
   BACKGROUND OF THE INVENTION 
   In conventional telephone systems, incoming calls cause a ringing sound to alert the recipient. Typically, a mechanical switch called a “hook” relays the incoming call&#39;s ring signal to a bell or loudspeaker to sound as long as the handset is on the hook, and relays incoming signals to the low volume speaker in the handset for conversation when the handset is lifted off the hook. 
   Internet telephony stations based on personal computers in many cases use a headset as illustrated in  FIG. 1 , which positions a small speaker over one ear of a user and positions a microphone in front of the user&#39;s mouth. Headsets are used, instead of a computer&#39;s loudspeakers, because audio feedback from the loudspeakers into its microphone could interfere with telephone conversations. Since headset speakers are positioned close to the listener&#39;s ear, their volumes are low. When the headset is not being worn, and the computer&#39;s loudspeakers are not in use, possible rings of incoming calls could go unnoticed. 
   SUMMARY OF THE INVENTION 
   The present invention provides a system for announcing incoming calls at Internet telephone stations based on personal computers equipped with headsets. The invention includes a routing circuit formed preferably of two different frequency bandpass filters, two analog switches, an amplifier and a speaker. 
   Initially, the computer sound card supplies an analog signal to the routing circuit, in which filters pass bands centered on two selected frequencies, preferably 520 Hz and 3250 Hz, characteristic of telephone ringing signals. Either bandpass filter outputting a signal closes a respective analog switch which connects the original, unfiltered analog ringing signal to the loudspeaker. The two analog switches are connected in series, so they must both be activated by their respective bandpass filters to allow the original analog ring signal to pass through to the loudspeaker. 
   Since the 520 Hz and 3250 Hz frequencies are both characteristic of a ring signal and, in ordinary conversations, not likely to occur together, both frequencies being present simultaneously in an incoming signal reliably indicates that it is a ring signal, so it is connected to the speaker. When not both frequencies are present, the soundcard&#39;s original analog signal is routed to its usual conversational destination, the headset. 
   This invention routes incoming ring signals to a speaker remotely from the headset that can be heard to alert recipients of incoming calls, and then, when the recipient has answered the incoming call, routes the conversation signal to the headset. 
   These and other benefits and advantages of the invention will become more apparent upon reading the following Detailed Description with reference to the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a prior art personal computer-based telephone with a headset; 
       FIG. 2  is a block diagram of a computer system operative as a telephony device with a routing circuit according to the present invention; 
       FIG. 3  is a flowchart of the operation of the routing circuit. 
       FIG. 4  is a flowchart showing specifics of step  320  of  FIG. 3 ; 
       FIG. 5  is a block diagram of the routing circuit of  FIG. 2 ; 
       FIG. 6  is a circuit diagram showing details of  FIG. 5 ; and 
       FIG. 7  is a block diagram showing a generalized version of the  FIG. 5  circuit. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The invention provides a system for extracting, routing and amplifying ring signals for incoming telephone calls. 
     FIG. 2  represents a computer system  200  equipped with a routing circuit for handling telephone ring signals according to the invention. System  200  preferably includes a Central Processing Unit (CPU)  210 , a video monitor  220 , an input/output interface  230 , memory  240 , and a soundcard  250  all inter-connected by a bus  260 , and further includes the routing circuit  270  of the invention, a headset  280  and an amplified speaker  290 . Bus  260  supplies analog or digital signals to soundcard  250 , which outputs analog signals on line  255  to routing circuit  270 , which in turn detects incoming calls and routes ring signals. 
     FIG. 3  is a flowchart of the invention&#39;s operation in filtering and diverting incoming call ring signals to a loudspeaker  290 . In step  310  an audio input signal is received (on  FIG. 2  line  255 ). Step  320  determines whether the input signal is a ring signal, indicating a new call. If so then step  330  routes the input signal to an amplifier and speaker  290  to alert the recipient. Alternatively, when the input signal is not a ring signal then step  340  routes the input signal to the headset  280 . 
   The invention can be embodied by hardware, software or firmware, and can be configured various ways in each of those media. The preferred embodiment, discussed below in conjunction with  FIGS. 4–7 , comprises a hardware circuit which searches the output of soundcard  250  for two selected frequencies. 
     FIG. 4  is a flowchart detailing sub-steps of  FIG. 3  step  320  in a preferred process  400  for identifying a ring signal from two specific frequencies. Initially, in a first step  410  the circuit receives an audio signal input (via bus  255 ) from the soundcard. This input signal is then, in steps  420  and  430 , checked for the presence of the two selected characteristic frequencies, 520 Hz and 3250 Hz. Either frequency may be checked first, or the frequencies may be checked simultaneously. If either frequency is not present then the incoming signal must not be a ring signal and therefore, in step  450 , is routed to the headset  280 . If the two frequencies are present simultaneously then in step  440  the incoming ring signal is routed to an amplifier (not shown) and a speaker  290 . 
     FIG. 5  is a block diagram of the ring signal detection circuit  270  in the preferred embodiment, which includes an audio input on line  255 , two bandpass filters  520  and  530 , two capacitors  540  and  550 , two analog switches  560  and  570 , a headset  580 , an audio amplifier  590  and a speaker  290 . 
   The audio input signal is taken from the soundcard  250  output  255  and divided into three branches  512 ,  515  and  516 . The first branch  512  is a bypass branch which carries the complete original unfiltered signal. The second branch  515  and third branch  516  include respective frequency bandpass filters  520  and  530 , each of which passes a different frequency from the input signal. 
   The criteria for the selection of bandpass filter frequencies are that the filtered input signal frequencies be characteristic of the telephone ringing sound, and that two frequencies be far enough apart to be easily distinguishable, to minimize the number of false detections. Bandpass filters are constructed of a low pass filter and a high pass filter connected in series, so it is difficult and expensive to build one with a narrow band, and more so for an arbitrary specific frequency. Selecting two frequencies which are far apart reduces the likelihood that either bandpass filter will pass both frequencies and cause false detects. 
   Since a telephone ring signal typically contains the two frequencies 520 Hz and 650 Hz along with harmonics of these frequencies, two of these frequencies can identify ring signals for incoming calls. The two bandpass filters  520  and  530  selected are preferably 520 Hz and 3250 Hz, which correspond to the fundamental of the 520 Hz signal and to the fifth harmonic of the 650 Hz signal. This wide spacing between the two selected frequencies loosens specifications and makes it less expensive to manufacture the filters. 
   A bandpass filter passes only signals within its specified frequency range. If the audio signal input on line  255  contains frequencies within this specified range, those frequencies will be passed, while frequencies outside this range will be blocked. Signals which pass bandpass filters  520  and  530  are applied to, and charge, respective capacitors  540  and  550 . Capacitors  540  and  550  are used to filter false detects, because conversations, noise and other sounds in the audio input besides ring signals can have the same frequency, but normally have briefer durations. However, telephone ring signals have a known duration, and a capacitor and time constant can be chosen to prevent the capacitor from being fully charged by signals which are too short. Thus, noise which slips through the bandpass filters  520  or  530  is filtered by capacitors  540  and  550 . If filtered signals persist longer than the time constant of the circuit, then the signals proceed to the respective analog switches  560  and  570 . 
   When the series-connected analog switches  560  and  570  both receive an input signal, they pass the complete unfiltered signal from branch  512  to the amplifier  590  and speaker  290 . 
     FIG. 6  shows details of the preferred circuit  600  components from  FIG. 5 . The input signal on line  255  enters the circuit  600  and is split into two branches. The first branch  601 , which is grounded through a 20 KΩ resistor  604  to common  603 , carries the signal through a 20 KΩ resistor  605 , a 0.39 μF capacitor  606 , another 10 KΩ resistor  607 , an audio operational amplifier  608  with a shutdown control pin and finally to a speaker  609 . The audio operational amplifier  608  has an input on line  675  coming from the analog switches for the shutdown control, is grounded to common through a 1 μF capacitor  610 , and is bypassed with a 96 KΩ resistor  611 . 
   The input signal on path  602  is also grounded through a 20 KΩ resistor  615  to common and passes through a 30 KΩ resistor  616  and a 1 μF capacitor  617  before being split into second branch  619  and third branch  618 . Both branches  619  and  618  carry the signal through respective 316 KΩ resistors before entering their respective bandpass filters  520  and  530 . The bandpass filters are connected through respective 604 Ω resistors  621  and  641  to a 2.5 volt source. Bandpass filter  520  includes four operational amplifiers  622 ,  623 ,  624  and  625  having one input set at 2.5 volts, two 100 KΩ resistors  626  and  627 , two 10 KΩ resistors  628  and  629 , two 1000 pF capacitors  630  and  631 , two 15.45 KΩ resistors  632  and  633  and one 51 KΩ resistor  634 . Bandpass filter  530  includes four operational amplifiers  642 ,  643 ,  644  and  645  having one input set at 2.5 volts, two 100 KΩ resistors  646  and  647 , two 10 KΩ resistors  648  and  649 , two 1000 pF capacitors  650  and  651 , two 96.6 KΩ resistors  652  and  653  and one 62 KΩ resistor  654 . 
   The two branches  520  and  530  have output lines  680  and  682  which carry their signals through 1 μF capacitors  661  and  668  respectively and then are grounded to common through inverters  662  and  664 , respectively. 
   At this point, branch  520  is split into a branch which carries the signal through rectifier  663  and on a path grounded to common in two places (by a 1 μF capacitor  666  and a 43 KΩ resistor  667 ) to analog switches  691  and  692 , and on a branch through rectifier  665  on a path which has a 120 KΩ resistor  669  and is grounded to common in two places (by a 1 μF capacitor  670  and by a 470 KΩ resistor  671 ). 
   Branch  530  carries the signal through a rectifier  672  to an analog switch  693  through a path which is grounded to common in two places through a 1 μF capacitor  674  and a 120 KΩ resistor  675 . When the analog switches  691 ,  692  and  693  are activated, the shutdown control of the audio operational amplifier  608  which is normally maintained at 5 volts through a 10 KΩ resistor  675  is grounded to common, thus activating the speaker  609 . 
     FIG. 7  is a block diagram of a generalized ring detection circuit, which includes an audio input  710 , a number N of frequency filters  720 ,  722  and  724 , a number N of capacitors  730 ,  732  and  734 , a number N of analog switches  740 ,  742  and  744 , a headset  750 , an audio amplifier  760  and a speaker  770 , where the number N can be any integer greater than or equal to one. The preferred embodiment discussed above and illustrated in  FIG. 4  and  FIG. 5  is a special case (N=2) of this generalized embodiment. A circuit designed with N=1 would contain one frequency filter  720 , one capacitor  730  and one analog switch  740 . The frequency filter could be a bandpass filter, low pass filter or high pass filter depending on the application. In such a circuit the detection of one frequency would be sufficient to identify an incoming call. A circuit designed with N=5 would contain five frequency filters, five capacitors and five analog switches. In such a circuit the detection of five frequencies would be necessary to identify an incoming call. 
   There are other embodiments which can extract and amplify a ringing signal from an incoming telephone call which are similar to this invention but have not been discussed. Although the present invention achieves this process through the use of hardware such as switches and filters, similar results can be achieved through the use of software, firmware and hardware combinations. For example, the soundcard can be set up to output its frequencies to a CPU which can be programmed to search for specific frequencies and, when the correct frequencies are found, send a tone signal to the computer speaker. Since an Internet telephone works by transmitting wave packets, a data server can announce a new call by sending a specific wave packet which contains information other than frequency. In such a case the hardware, firmware and software would receive the signal, determine that it is an incoming call and command the speaker to make an announcement bypassing the headset.