Patent Grant
8514068
Wireless monitors are commonly used during exercise, athletic competitions, medical tests and other activities. For example, a heart rate monitor can be worn by a user, contacting the user at a suitable location such as the chest or wrist. A chest-worn monitor may detect an electrocardiogram (EKG) signal of the user's heart, each time a heart beat occurs, and transmit a corresponding pulse in a wireless signal to a receiver unit, where the signal is further processed to determine the heart rate. The receiver unit typically includes a display device which displays the heart rate to the user or other person. For example, the receiver unit can be worn on the user's wrist, provided in a console or other unit which is mounted to an exercise device such as a treadmill or bicycle, or provided in a portable or stationary device which is monitored by an athletic trainer, medical personnel or others.
In addition to monitoring of a heart rate, monitors are available for monitoring other bodily actions, such as breathing, or repetitive physical movements which are performed by a user during exercise, such as steps taken while running, or pedal revolutions during bicycling, and so forth. However, when wireless monitors are used in the same location, crosstalk can occur, preventing the receiver unit from accurately determining a rate at which the bodily action is performed. Other noise sources can also prevent the receiver unit from distinguishing the signal from a monitor. To this end, techniques have been developed for encoding additional identifying data onto the wireless signal. However, the existing approaches have drawbacks such as increased cost, power consumption, and complexity and susceptibility to additional sources of electromagnetic interference.
A user-worn monitor, receiver unit and associated methods are provided for interference-tolerant telemetric signal detection.
In one embodiment, a receiver unit includes a receiver circuit, an amplifier circuit, a microprocessor associated with the amplifier circuit and an output device associated with the microprocessor. The receiver circuit receives a wireless signal from a user-worn monitor, where the wireless signal includes respective pulses generated by the user-worn monitor. Each respective pulse is generated when a respective instance of a bodily action of the user is detected, and the respective pulses include identifier pulses which each have a duration or width which identifies the user-worn monitor, interspersed among other pulses. The amplifier circuit provides an amplified signal based on the wireless signal. The microprocessor operates in a crosstalk tolerant mode in which it processes the amplified signal to interpret the duration of each of the identifier pulses as an identifier of the user-worn monitor. In this mode, the microprocessor also synchronizes with the identifier pulses, and determines a rate of the bodily action based on (a) time intervals between the identifier pulses and (b) a number of pulses between the each of the identifier pulses. The output device provides an output such as a display and/or audio output, based on the rate.
In another embodiment, a receiver unit includes a receiver circuit, an amplifier circuit associated with the receiver circuit, a microprocessor associated with the amplifier circuit, and a display device associated with the microprocessor. The receiver circuit receives a wireless signal from a user-worn monitor, where the wireless signal includes respective pulses generated by the user-worn monitor. Each respective pulse is generated when a respective instance of a bodily action of the user is detected, and the respective pulses include: (a) at least two consecutive identifier pulses which each have a duration which identifies the user-worn monitor, and (b) other pulses. The amplifier circuit provides an amplified signal based on the wireless signal. The microprocessor processes the amplified signal to interpret the duration of each of the at least two consecutive identifier pulses as an identifier of the user-worn monitor, determines a time interval between each of the at least two consecutive identifier pulses, synchronizes with the other pulses based on the time interval, and determines a rate of the bodily action based on timing of the other pulses (as well as timing of the at least two consecutive identifier pulses). The output device provides an output based on the rate.
In another embodiment, a user-worn monitor includes an amplifier circuit, a microcontroller associated with the amplifier circuit, and a transmitter associated with the microcontroller and the amplifier circuit. The amplifier circuit receives a signal regarding a bodily action of a user and provides a corresponding amplified signal. The transmitter provides a wireless signal based on the amplified signal, where the wireless signal includes respective pulses. Each respective pulse is generated when a respective instance of the bodily action is detected, and the respective pulses include identifier pulses which each have a duration which is set in response to the microcontroller to identify the user-worn monitor, interspersed among other pulses.
Corresponding methods may also be provided, along with a tangible processor-readable medium which stores code which is executable by a microprocessor to perform the methods described herein.
a depicts an example long burst which is transmitted by a monitor.
b depicts an example short burst which is transmitted by a monitor.
a depicts a time line of a wireless signal transmitted by a monitor, where a single long pulse is used in a cycle.
b depicts a time line of the wireless signal of
c depicts a time line of the wireless signal of
d depicts a time line of a wireless signal transmitted by a monitor, where a single long pulse is used after every Z seconds.
a depicts a time line of a wireless signal transmitted by a monitor, where two long pulses are used in a cycle.
b depicts a time line of the wireless signal of
c depicts a time line of the wireless signal of
Difficulties which are encountered by the presence of crosstalk and other forms of interference in a wireless signal are overcome to enable accurate communication between a user-worn monitor and an associated receiver unit. At the same time, advantages are achieved with regard to cost, power consumption, complexity and susceptibility to electromagnetic interference.
It is also useful to measure repetitive bodily actions such as repetitive physical movements which are performed by a user during exercise, such as steps taken while walking or running, pedal revolutions during bicycling, and so forth. Other examples include jump rope skips, and bodily action related to calisthenics such as lunges, jumping jacks, sit-ups, stomach crunches, push-ups, pull-ups, squats, calf-raises, toe touches, and dips. Other examples of repetitive bodily actions include muscle movements performed during weight training, such as leg or arm curls, bench presses, and some of the calisthenics which can be performed using weights.
For instance, a pedometer or step counter can be worn on the user's belt to detect repeated movements which are performed during walking or running. A pedometer typically employs a mechanical or electrical sensor, such as a micro-electromechanical system (MEMs) inertial sensor. Wrist worn devices are also available which use an accelerometer to count repetitive movements during weight training, such as sets and repetitions. For example, a set may include ten repetitions. An example is the POLAR F55®. Similarly, monitors which can be worn on top of a shoe, such as monitor 114 are available. An example is the POLAR 51 FOOTPOD®. In this product, an inertial sensor and DSP (digital signal processor) provide real time running speed, pace and distance. Such a product can be used during running or cycling, for instance. Monitors which are built in to a shoe or clothing are also available. Examples are provided by products under the brand of ADIDAS®-POLAR® PROJECT FUSION™. The techniques provided herein can be incorporated into products of these types, among others.
In the example provided, the user has a monitor 114 worn on his shoe 116 as well as the chest-worn monitor 102. The monitors 102 and 114 transmit wireless signals which indicate when a repetition of the monitory bodily activity has occurred. For example, the monitor 102 as a heart rate monitor can transmit a pulse or burst each time a heart beat is detected. In one approach, a pulse can include a signal modulated at a relatively low frequency of 5.3 kHz, or more generally, between 4.8 kHz and 5.8 kHz. Such low frequency signals are advantageous since they do not typically require approval by a government agency such as the FCC in the United States.
High frequency signals can also be used. An example is a 2.4 GHz signal. Such high frequency signals require a faster processor and thus may be more expensive and consume more power, and government approval may be required. Also, unlike low frequency signals, they are also susceptible to interference from electronic devices such as microwave ovens, cell phones, computers and wireless local area networks (WLAN) base stations used in computer networks.
The monitor 114 as a pace monitor can transmit a signal each time a step is detected. Similarly, the monitor 114 could detect a revolution of the user's feet, e.g., a chain ring revolution, on a stationary or moving bicycle as the user pedals while wearing the shoe 116.
A wireless signal transmitted from a monitor can be received at a receiver unit, where the signal is processed to provide an output in a visible and/or audible form for the user or other person. In some cases, the monitor transmits only and does not receive wireless signals or other signals while operating.
A console 120 is an example of a receiver unit. A console 120 can be mounted to exercise equipment such as a bicycle, treadmill, or stair climber machine, for instance, in a position in which it provides a display to the user 100. Or, the console 120 can be mounted or handheld, for use by another person such as an athletic trainer or medical personnel. In this example, the console has a display with a region 122 which provides a current heart rate, e.g., 120 beats per second (bps), a region 124 which indicates a elapsed exercise time, a region 126 which indicates a number of calories burned in the exercise session, and a region 128 which is a bar chart showing a history of the heart rate, e.g., over the past few minutes, relative to a target heart rate range which is between maximum (max) and minimum (min) levels. The console can also provide an audible output such as an alarm when the heart rate moves outside the target heart rate range, to signal to the user to move faster or slower.
Another example of a receiver unit is a wrist worn device 130 which provides an output in the form of a display of the current heart rate or other detected rate, for instance. An audible alarm or other output can also be provided as discussed. The receiver unit can be wrist worn, similar to a wrist watch, and may in fact have time keeping ability as well as the ability to provide an output based on the received wireless signal.
Another example of a receiver unit is a portable device 140 such as a cell phone, media player, personal digital assistance (PDA) or similar device. Such a device can be held in the user's hand or attached to the user's body, e.g., using a strap, or placed in a pocket of clothing worn by the user. The portable device 108 is held in an arm strap 106 as an example. The monitor 102 or 114 can communicate with the portable device 108 via a low frequency signal with the use of appropriate circuitry as described herein. The portable device 140 can provide a visual or audible output as discussed. In one approach, the user can receive an audible input from the portable device via an earphone such as an ear bud 112 which is connected by a wire 110 to the portable device 108. Such earphones are commonly used with portable media players. The audible output can include a synthesized voice which states the current heart rate at specified intervals, when the current heart rate is out of the target zone, or at other specified times.
Another example of a receiver unit is a wireless ear-worn device 150 which is similar to devices used to communicate with cell phones using Bluetooth (IEEE 802.15.1) transmissions. The monitor 102 or 114 can communicate with the ear-worn device 150 with the use of appropriate circuitry. Or, the monitor 102 or 114 can transmit a wireless signal to the portable device 140 such as a cell phone, where the portable device 140 in turn communicates with the wireless ear-worn device 150 to provide an audible output to the user 100, as discussed above. Many other variations are possible. Moreover, the wireless signal from a monitor can be received and processed by more than one receiver unit. In addition to real-time processing and updating of a heart rate or other parameter at a receiver unit, the receiver unit can record data from a monitor in a non-volatile memory such as a computer hard drive or flash memory for subsequent analysis.
Thus, the transmitter can comprise an inductive resonator which provides each pulse in the wireless signal as an inductive burst, and the pulses generated by the monitor 200 each comprise an inductive burst, in one embodiment. The microprocessor 210 may access a memory 208 which includes code which is executable by the microprocessor 210. The memory 208 may include a tangible storage device such as a non-volatile memory, e.g., ROM, and a volatile memory, e.g., RAM, which store processor-readable code which is executed by one or more microprocessors to implement the functionality described herein.
As an option which reduces power consumption and cost, the output from the amplifier circuit 130 can be provided to a threshold detector. The threshold detector provides a digital output based on the level of the input. This digital output can be used to indicate the onset of a detected heart beat or other bodily action. In this case, no A/D conversion is needed. Microprocessor 210 can also run at a lower clock speed to save power.
The receiving unit 220 includes a receiver circuit 222, amplifier 224, microprocessor 228, memory 226 and output device 230. The microprocessor 228 may include a free running counter 229 which is used to select an identifier, as discussed below in connection with
a depicts an example long burst which is transmitted by a monitor.
In one embodiment, the duration of a burst is used as an identifier of the monitor, and different durations can be used to identify different monitors. With this type of positive identification, crosstalk and other types of interference can be handled. A long burst represents a pulse or burst whose duration is noticeably longer than a nominal, short burst. A short burst can be 5-10 milliseconds (msec.) for instance, while a longer burst can range from 20-250 msec., for instance. The long burst can be 2× or more longer than the short burst. The upper limit of the long burst depends on the application. For heart beat detection, a heart rate of 30-240 bpm may be covered. 240 bpm, or 4 beats per second, translates to a period between beats of 250 msec. The duration of the long burst should be less than the period between detected bodily events. In practice, a longer burst uses more power so the long burst need not be at the upper allowable limit. A long burst should have a duration which allows the burst to be distinguished from a short burst and from other long bursts. As an example, a long burst can be, e.g., at least 5-10 msec. longer than a short burst.
As a result, a predefined set of different durations which are identifiers for different user-worn monitors can be provided and stored in the monitor and receiver unit. Additionally, a binary code word can be assigned to each duration. For example, with 25=32 code words, and a 5 msec. difference between long pulses, long pulse durations of 10, 15, 20, . . . , 155, 160, 165 msec. can be used in the predefined set. Corresponding example five-bit code words are 00000, 00001, 00010, . . . , 11101, 11110, 11111, respectively.
a depicts a time line of a wireless signal transmitted by a monitor, where a single long pulse is used in a cycle. The long pulse is an identifier pulse because its duration is used by the receiver unit as an identifier of the monitor. In one approach, a cycle includes a predefined number N of pulses. One or more long pulses can be provided in each cycle, or in every nth cycle, where n≧1. Moreover, the monitor and receiver unit can be preconfigured with knowledge of the number of pulses per cycle. Two example cycles 400 and 410 are depicted. Time increases moving to the right hand side of the figure. The pulse sizes and shapes are not necessarily to scale. In this example, one long pulse is provided per cycle, at t0 and t5. Additionally, the long pulse is at the start of a cycle, although this is not required. In each cycle, the long pulse is followed by other, shorter pulses of equal duration, e.g., 5-10 msec. Four short pulses are used as an example at t1-t4 and t6-t9.
Another option is to use all long pulses in each cycle. However, using a minimal number of long pulses mixed or interspersed among short pulses allows a monitor to be identified by a receiver unit while minimizing power consumption by the monitor. Generally, a long pulse can be transmitted every X beats, Y consecutive times to allow the receiver unit to synchronize to the correct monitor. X and Y can be integers which are greater than or equal to one. As an alternative, one or more long pulses can be transmitted in response to the first detected bodily action after every Z seconds, as discussed in connection with
In
b depicts a time line of the wireless signal of
In some cases, a receiver unit can detect when crosstalk is present. For example, when the long pulse at t0 is received, the receiver unit can determine an expected time to receive a next pulse, particularly if information from previous pulses has been used to determine a current rate of detection of the bodily action. Typically, the time interval between successive pulses will be relatively uniform, so that an expected time interval at which a next pulse is received can be estimated with good accuracy based on the time interval at which the last pulse was received. Thus, knowing that a next pulse should be received at or near t1, the presence of the crosstalk pulse at t0a can be identified as crosstalk, and ignored, by a receiver unit. Another example technique to detect crosstalk involves detecting the amplitude of each pulse, where higher amplitude pulses are assumed to be from the subject monitor, based on the assumption that the subject monitor is closer to the subject receiver unit than the crosstalk monitor. See US patent application publication no. US2009/0043217 to Hui et al., published Feb. 12, 2009, and incorporated herein by reference, for further details.
In some cases, the crosstalk pulses may be sufficiently close to the pulses of the subject monitor so that the receiver unit cannot distinguish the correct pulses. In such cases, the microprocessor of the receiver unit can enter a special crosstalk mode in which it only synchronizes with the long pulses, but not the short pulses, to determine the rate of the bodily action. The rate can be determined knowing the time interval between the long pulses and the number of short pulses between the long pulses. For example, a rate based on the long pulses at t5 and t0, with four pulses between them, is 5 beats/(t5—t0). In this case, the rate is updated less often than every pulse. The microprocessor can continue to detect the short pulses, whether they are crosstalk or not, to determine when crosstalk is no longer present at a threshold level, and to return to another, baseline mode in which case the microcontroller of the receiver unit synchronizes with each pulse to update the rate.
A threshold level of crosstalk can be defined which the microcontroller uses to determine whether to change its operating mode. The threshold level may be met, e.g., if one or more crosstalk pulses are detected in one or more cycles, even if it is determined that they have highly inconsistent timing and therefore can be ignored. Or, the threshold level may be met if a specified number of crosstalk pulses are detected in a cycle, and this is repeated for a specified number of cycles. Or, the threshold level may be met if one or more crosstalk pulses are detected which render it impossible to accurately detect the short pulses in one or more cycles. Or, the threshold level may be met if one or more crosstalk pulses are detected which have a specified amplitude, such as an amplitude which is a specified portion of the non-crosstalk pulses. Or, the threshold level may be met if one or more crosstalk pulses are detected which have a discernible amplitude. Other definitions of the threshold level may be used as well.
The microprocessor can change back and forth between the crosstalk mode and the baseline mode as the level of crosstalk changes over time. In this way, the highest possible update rate is maintained whenever possible.
In this example, the monitor of the subject user provides a long pulse as an identifier in each cycle, while the crosstalk is provided by a crosstalk monitor which does not use a long pulse. Another example scenario, discussed next, involves both monitors using long pulses.
c depicts a time line of the wireless signal of
A further mechanism for detecting crosstalk is to compare the duration of each long pulse to the known duration which has been associated with the subject monitor. If the duration is inconsistent with the known duration, either shorter or longer by a specified margin such as 1-2 msec., the long pulse can be determined to be crosstalk. Moreover, a determination that crosstalk is present can be based on analysis of the duration and/or timing of more than one pulse. In this case, a pulse that appears to be crosstalk may not trigger the crosstalk mode in the microprocessor of the subject receiver unit until the determination is confirmed by one or more other pulses in the same cycle and/or one or more other cycles. A pulse that appears to be crosstalk can be ignored or skipped at the subject receiver unit for purposes of determining a rate of received pulses. The timing of the next pulse which does not appear to be crosstalk, with knowledge of the number of skipped pulses, can be used to determine the next updated of the rate, in one approach.
In some cases, a crosstalk pulse may overlap with a pulse from the subject monitor such that a pulse from the subject monitor is corrupted and appears to be longer than it is. In such cases, the enlarged pulse may be ignored by the subject receiver unit, and the next uncorrupted pulse used to determine the rate. Generally, crosstalk reduction is a probabilistic technique which attempts to account for the most probable scenarios.
d depicts a time line of a wireless signal transmitted by a monitor, where a single long pulse is used after every Z seconds. Instead of transmitting a long pulse based on a pulse position within a cycle or based on a pulse count, one or more long pulses can be transmitted based on specific time intervals. Fixed or varying intervals can be used. In an approach which uses a fixed interval, a long pulse is transmitted based on a specified period such as every Z seconds. For example, assume a period begins at tz1, just before the long pulse at to, and Z seconds later occurs just before t6, at t2z. The period is t2z-t1z. In this case, the next pulse after t2z which is transmitted will be a long pulse, at t6. In this approach, the number of short pulses between long pulses can vary as the rate of the detected bodily action varies. In one approach, the heart rate is based on the temporal spacing of each pulse, including both the long and short pulses.
a depicts a time line of a wireless signal transmitted by a monitor, where two long pulses are used in a cycle. By having multiple long pulses in a cycle, timing information can be gained faster by the receiver unit even when the presence of crosstalk renders undistinguishable the other, short pulses which are meant for the receiver unit. Thus, the receiver unit can synchronize sooner with the monitor. For example, long pulses are provided at t0 and t1 in a cycle 500, and at t5 and t6 in a cycle 510. Short pulses are provided at t2-t4 and t7-t9. The long pulses can be consecutive but this is not necessary as long as their relative positions (e.g., the number of short pulses between them, which is zero or more) is known. Here, once the long pulses at t0 and t1 are received, the interval between them indicates a rate, as well as the expected interval of the next pulse, which is a short pulse in this example. Thus, the rate can be determined right away, and the presence of a pulse which is inconsistent with the expected timing can be identified as crosstalk.
b depicts a time line of the wireless signal of
c depicts a time line of the wireless signal of
Variations and combinations of the approaches in
Step 602 includes determining a pulse duration to use for transmission. A monitor may be hard-coded with a specific long pulse duration to use, or it may selected the duration from a predefined set of different durations which are identifiers for different user-worn monitors. For example, the predefined set can be stored in the memory 226 of the receiver unit (
In one approach, the microprocessor uses a free running counter 229, which is a counter than is constantly up from zero, for instance, until a maximum value is reached, at which time the counter restarts the counting. Such a counter can be implemented in hardware, for instance, and provide a value which is mapped to one of the available durations. The value of the count can be stored and accessed from a memory register. A non-deterministic selection of a duration includes a random or pseudo-random selection. Other possible techniques for selecting a duration use a random number generator which is realized by hardware and/or software. A random number generator can be implemented by a software algorithm that runs continuously with an output number that changes randomly. Another approach is to determine the long pulse duration by counting random events such as a start or end of a session. Another approach is to determine the long pulse duration based on a rate acquisition time or the rate itself. For example, when a user ends an exercise session and removes the monitor, the monitor can record and store the current rate based on the timing between the last two consecutive transmitted pulses. This stored value can be accessed when a new session is later started and used as a seed input to a random number generator, for instance, to determine a value which is mapped to one of the predefined available pulse durations.
As discussed, various transmission patterns can be used. Generally, the transmission includes long pulses interspersed among other, short pulses. The long pulses can appear consecutively and/or non-consecutively. A transmission pattern can be used based on repeated cycles, where each cycle has the same pattern, and one or more long pulses are in predefined positions within a cycle, interspersed among the short pulses. The one or more long pulses in a cycle can be at the start of a cycle or other relative position within a cycle, in a cycle-based pattern. Or, a time-based pattern can be used, e.g., as discussed in connection with
At step 604, the monitor receives a signal regarding a bodily action, such as an EKG signal indicating that a heart beat has occurred, or a signal from a pedometer which indicates that the user has taken a step or performed an instance, e.g., occurrence, of a repetitive physical movement during exercise. For example, the repetitive movement may be jogging, where an instance of the movement is each step. Where the repetitive bodily action is the heart beating, an instance of the bodily action is one heart beat. At step 606, the monitor amplifies the signal. At decision step 608, if a condition is met for transmitting a long pulse, the monitor transmits a long pulse, at step 612. The condition can be based on a cycle-based pattern or a time-based pattern, for instance, as discussed.
At decision step 608, if the condition for transmitting a long pulse is not met, the monitor transmits a short pulse, at step 610. At step 614, a pulse counter is incremented. The pulse counter can be used to track the current position within a cycle and to determine when to start a new cycle. The monitor waits to receive the next signal regarding the bodily action, at step 604, or the session ends at step 616.
A session can end when the user takes the monitor off, or manually turns the monitor off, for instance. A timeout period such as several seconds may be enforced by the monitor and/or receiver unit before the session of exercise is determined to end, at which time the identification of the monitor may be discarded. In a subsequent new session, the monitor can select another pulse duration as its identifier, and the receiver unit again identifies the monitor based on the newly-chosen duration of the identifier pulses. For example, a session can be defined as a time period in which a user wears a chest strap, where the end of the session occurs when the user removes the chest strap. The microcontroller of the monitor can be configured so that the intermittent disconnection of the chest strap does not create a new session. For example, if the removes the chest strap but reattaches it within next “x” seconds (e.g., 15, 30 or 60 seconds), the session is maintained, but if there is a gap of more than “x” seconds, a new session is started and assigned a new long pulse width.
In this case, the pulse duration and therefore the monitor identifier is dynamic. Or, the pulse duration may be hard-coded into a matched set of a monitor and a receiver unit, and different respective pulse durations may be hard-coded into different respective matched monitor-receiver unit sets.
The communication may be one-way from the monitor to the receiver unit so that the long pulse duration is not changed once a session begins.
At step 704, the pulse is amplified. At step 706, the pulse duration is determined, e.g., as the time interval between the leading and trailing edges of the pulse. At decision step 708, if the pulse is a long pulse, decision step 710 determines if it is the first long pulse of the session. If it is the first long pulse of the session, its duration is stored as an identifier of the monitor at step 714. Data which represents the duration itself as a time value can be stored, or the duration can be mapped to a code word which is stored. An additional check can be made to ensure that the duration is consistent with a predefined set of durations which are available identifiers of different monitors. For example, the duration may be required to match, within a tolerance, one of the available durations.
At decision step 710, if the long pulse is not the first long pulse of the session, a decision step 712 determines if the duration matches a previously-stored duration within a tolerance of, e.g., +/−1-2 msec. If there is a match, the microcontroller synchronizes to the pulse at step 724. That is, the microcontroller uses the timing of the pulse. At step 726, the rate of the bodily action is updated based on the pulse, and at step 728, the newly-updated rate is provided to an output device. A next pulse is then received at step 702.
If decision step 712 determines that the pulse duration does not match the stored duration, a crosstalk mode can be set for the microprocessor at step 722, in one possible approach. As mentioned previously, various criteria can be used to determine whether a threshold level of crosstalk is detected and to decide whether or not to set a crosstalk mode to accommodate the crosstalk. The mode can switch from the crosstalk mode back to the baseline mode if certain conditions are met, at step 716, such as the crosstalk level falling below a threshold level. Switching between modes may be controlled so that it does not occur too frequently. For example, mode switching may occur only after a time interval has passed or a minimum number of pulses have been detected. A next pulse is then received at step 702.
If decision step 708 determines that the current pulse is not a long pulse, decision step 718 determines if the crosstalk mode has been previously set. If the crosstalk mode is set, steps 716 and 702 follow. In this case, the microprocessor does not synchronize to the short pulse so that its timing information is not used to update the rate. If the crosstalk mode is not set at decision step 718, decision step 720 determines if a threshold level of crosstalk is currently detected. If the threshold level of crosstalk is detected, the crosstalk mode is set at step 722. If decision step 720 determines that the threshold level of crosstalk is not detected, steps 724, 726 and 728 are performed as discussed.
Generally, when the receiver unit is powered on and the monitor is transmitting, a time period of a few seconds may pass before the receiver unit synchronizes to the monitor and outputs a rate. During this time period, or after, the receiver unit sees a long duration pulse and uses it as an identifier of the monitor, and continues its synchronization with that monitor.
The foregoing detailed description of the technology herein has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the technology to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. The described embodiments were chosen to best explain the principles of the technology and its practical application to thereby enable others skilled in the art to best utilize the technology in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the technology be defined by the claims appended hereto.
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