Abstract:
A system, fan controller and method for enhanced alert notification. Embodiments provide an effective mechanism for utilizing system fans to create alert tones or messages, where fan speed differentials may be adjusted to alter the frequency of the fan interference sounds. As such, existing hardware can be used to reduce cost by producing audible alerts which may be heard above ambient noise in a room with one or more electronic systems. Further, the frequency of the interference sounds may be altered to more clearly identify one or more systems to which a fault pertains.

Description:
RELATED APPLICATIONS 
   The present application is related to and claims the benefit of U.S. Provisional Application No. 60/722,626, filed Sep. 29, 2005, entitled “FAN CONTROLLER WITH ALERT CAPABILITY,” naming Steven P. Larky and Darrin Vallis as the inventors, assigned to the assignee of the present invention. That application is incorporated herein by reference in its entirety and for all purposes. 

   BACKGROUND OF THE INVENTION 
   Many electronic systems require cooling to dissipate heat generated by electronic components. Since radiation and conduction are less-effective heat transfer methods in an enclosed system, convective cooling solutions are often used. As such, a common electronic system may have one or more fans to drive air over components, exhaust warm air from the system and draw cooler air into the system. 
   Regardless of the implementation, a spinning cooling fan will emit some noise. Noise often results from the fan motor bearing, air moving past the fan blades and body of the fan, and the placement of the fan with respect to other objects (e.g., a vent in an electronic system chassis). Additionally, a more pronounced noise may result from multiple fans spinning at different speeds, where the noise profiles from the fans intersect to produce a “beating” sound. Given that the beating sound is often much louder and more annoying than the sound from an individual fan, conventional fan controllers attempt to spin proximately-located fans at precisely the same speed to reduce the beating sound. 
   Although the reduction of fan interference sounds is often important in a single electronic system with multiple fans, it becomes even more of an issue when multiple systems are placed in proximity to one another (e.g., in a computer server room). Since each system is likely to have at least one fan, the placement of multiple systems in the same room can dramatically increase the number of fans which may interfere with one another and create beating sounds. And moreover, given that the ambient air temperature of rooms containing multiple systems is often higher than rooms containing a single system, systems designed to be placed in the presence of other systems often contain more fans or larger fans that produce more noise. As such, the beating sounds are often louder, more prevalent and more annoying than those associated with a single system. 
   Despite attempts by conventional fan controllers to spin fans at the same speed, some fan speed differential and associated beating sound is likely to remain, especially in environments with multiple systems. Additionally, even if all fan speed differentials were eliminated, the ambient noise from the many fans is often very loud even without any beating. As such, it is often hard to identify audible faults. And even if a fault is identified, it is often hard to discern which system a given fault is associated with. Similarly, given the large number of solid and blinking lights on multiple systems placed near one another, visual faults (e.g., a blinking light) are also hard to identify and distinguish. Thus, given that most electronic systems are equipped with such audible and visual fault indicators, the price of the systems is increased while still providing poor fault indication. 
   SUMMARY OF THE INVENTION 
   Accordingly, a need exists for improved alert notification in a computer system environment. A need also exists for alert notification with reduced system cost. Additionally, a need exists for alert notification which more clearly identifies which system or systems to which a fault pertains. Embodiments of the present invention provide novel solutions to these needs and others as described below. 
   Embodiments of the present invention provide a system, fan controller and method for enhanced alert notification. More specifically, embodiments provide an effective mechanism for utilizing system fans to create alert tones or messages, where fan speed differentials may be adjusted to alter the frequency of the fan interference sounds. As such, existing hardware can be used to reduce cost by producing audible alerts which may be heard above ambient noise in a room with one or more electronic systems. Further, the frequency of the interference sounds may be altered to more clearly identify one or more systems to which a fault pertains. 
   In one embodiment, a system includes a first fan and a fan controller coupled to the first fan and operable to control the first fan. The system also includes a first interface coupled to the fan controller for receipt of alert signals. The alert signals may be associated with one or more components of the system (e.g., ethernet hardware, power supply, etc.) and may indicate a condition warranting attention (e.g., battery low, power failure, component failure, overheated component, required system reboot, etc.). Alternatively, the alert signal may be that which is optionally routed to a light-producing device, speaker, etc. Additionally, the fan controller is further operable to vary a speed differential between the first fan and a second fan, wherein the speed differential is operable to create an audible sound, and wherein a variation in the speed differential is used to change a frequency of the audible sound in response to a received alert signal. As such, one or more fans may be used to create an audible alert from a received alert signal, where the frequency of the audible alert may be varied such that the alert comprises speech, music, a siren, or the like. Thus, not only may the alert be heard above ambient room noise, but the alert may more clearly identify one or more systems to which a fault pertains. 
   In another embodiment, a fan controller includes a first interface for receiving an input signal. A processor is coupled to the first interface, where the processor is for generating an alert signal in response to a received input signal. A fan speed control is coupled to the processor, where the fan speed control is for varying a speed differential between a first fan and a second fan in response to a received alert signal. The speed differential is operable to create an audible sound representing an alert, where a variation in the speed differential is used to change a frequency of the audible sound in response to the received alert signal. Additionally, the fan controller may include a memory coupled to the processor for storing alert information, where the processor is operable to determine a portion of the alert information associated with the received input signal, and where the portion of alert information is used to generate the alert signal. Further, the fan controller may also include a second interface coupled to the processor and for receiving temperature signals associated with a plurality of hardware components cooled by airflow from at least one of the first fan and the second fan, and wherein the fan controller is operable to change a speed of at least one of the first fan and the second fan in response to a received temperature signal. 
   And in yet another embodiment, a method for enhanced fault notification includes receiving an input signal. An alert signal is generated in response to receipt of the input signal, wherein the alert signal is operable to control a speed differential between a first fan and a second fan, and wherein the speed differential is operable to create an audible sound. The speed differential is varied to change a frequency of the audible sound. Additionally, a portion of alert information associated with the input signal may be determined, wherein the portion of alert information is used to generate the alert signal. Further, the method may include receiving a temperature signal associated with a plurality of hardware components, wherein the plurality of hardware components are cooled by airflow from at least one of the first fan and the second fan. A speed of at least one of the first fan and the second fan may be adjusted in response to the temperature signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements. 
       FIG. 1  shows an exemplary fan speed graph of a variable-speed fan and a constant-speed fan in accordance with one embodiment of the present invention. 
       FIG. 2  shows a block diagram of an exemplary fan controller coupled to a fan in accordance with one embodiment of the present invention. 
       FIG. 3  shows a block diagram of an exemplary fan controller in accordance with one embodiment of the present invention. 
       FIG. 4  shows an exemplary fan speed graph of two variable-speed fans in accordance with one embodiment of the present invention. 
       FIG. 5  shows a block diagram of an exemplary fan controller coupled to multiple fans in accordance with one embodiment of the present invention. 
       FIG. 6  shows a block diagram of an exemplary fan controller coupled to multiple fans with external fan speed controls in accordance with one embodiment of the present invention. 
       FIG. 7  shows a block diagram of an exemplary fan controller coupled to multiple fans with external and internal fan speed controls in accordance with one embodiment of the present invention. 
       FIG. 8  shows a process for enhanced alert notification in accordance with one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. While the present invention will be discussed in conjunction with the following embodiments, it will be understood that they are not intended to limit the present invention to these embodiments alone. On the contrary, the present invention is intended to cover alternatives, modifications, and equivalents which may be included with the spirit and scope of the present invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, embodiments of the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present invention. 
     FIG. 1  shows exemplary fan speed graph  100  of a variable-speed fan and a constant-speed fan in accordance with one embodiment of the present invention. As shown in  FIG. 1 , a first fan speed  110  and second fan speed  120  are graphed with respect to time. First fan speed  110  represents a variable-speed fan, whereas second fan speed  120  represents a fan spinning at a substantially-constant speed. As such, variation of first fan speed  110  with respect to second fan speed  120  creates fan speed differentials (e.g., first fan speed differential  130  and second fan speed differential  140 ), where the differential between the two fan speeds may vary with respect to time. For example, first fan speed differential  130  is larger than second fan speed differential  140 . 
   If a first fan whose speed may be represented by first fan speed  110  is located close enough to a second fan whose speed may be represented by second fan speed  120 , a fan interference sound (e.g., a “beating” sound) may occur. The fan interference sound can be caused by an intersection of the noise profiles of the two fans, where a “beat” may be produced by a summation of the amplitudes of the noise profiles. As such, the first and second fans may be located within the same system (e.g., a computer system, computer server, etc.), or located in different systems that are near enough to produce a fan interference sound. Alternatively, one fan may be located with a system, while the other fan may be located outside a system (e.g., as part of a HVAC system, a room fan, etc.). 
   The frequency of the fan interference sound may vary based upon the magnitude of the fan speed differential. As such, the speed of the first fan (e.g., represented by first fan speed  110 ) may be varied to change the magnitude of the fan speed differential, thereby altering the frequency of the resulting interference sound. In one embodiment, an increase in the magnitude of the fan speed differential may decrease the frequency of the fan interference sound, whereas a decrease in the magnitude of the fan speed differential may increase the frequency of the fan interference sound. For example, first fan speed differential  130  may produce a lower frequency interference sound than second fan speed differential  140  given that differential  130  is larger than differential  140 . 
   Additionally, the intensity or sound level of the resulting interference sound may be varied by increasing or decreasing the speed of the fans. For example, an increase in the average speed of the fans (e.g., those represented by fan speeds  110  and  120 ) may contribute to an increase in intensity of the fan interference sound. For example, first fan speed differential  130  is depicted in  FIG. 1  with a larger average fan speed than second fan speed differential  140 , and therefore, the fan interference sound corresponding to fan speed differential  130  may be more intense than a fan interference sound corresponding to fan speed differential  140 . Conversely, if the average speed of the fans decreases, then the intensity may reduce. As a further example, if the speed of both fans change with little change in the magnitude of the fan speed differential, then an increase in speed of the fans would create an increase in the average fan speed, thereby increasing the intensity of the interference sound. Conversely, if the speed of both fans reduces with little change in magnitude of the fan speed differential, then the intensity of the interference sound may decrease given a drop in average fan speed. 
   Although  FIG. 1  depicts a specific relationship between the speeds of two fans (e.g., fan speed  120  is constant and fan speed  130  follows a depicted speed variation), it should be appreciated that the two fan speeds may be alternatively represented in other embodiments. For example, second fan speed  120  may vary in other embodiments, or alternatively, may comprise a combination of constant and varying periods. Similarly, first fan speed  110  may be alternatively varied, or in another embodiment, may comprise a combination of constant and varying periods. 
   Additionally, although  FIG. 1  depicts a change in the magnitude of a fan speed differential for only two fans, it should be appreciated that more than two fans may produce fan interference sounds in other embodiments. As such, one or more fan interference sounds may co-exist based on one or more fan speed differentials. Thus, a resultant frequency and/or intensity of the fan interference sound may be based on a combination of multiple fan interference sounds. 
     FIG. 2  shows block diagram  200  of an exemplary fan controller coupled to a fan in accordance with one embodiment of the present invention. As shown in  FIG. 2 , fan controller  210  is coupled to fan  220  for controlling its speed in response to temperature and/or alert inputs. The speed of fan  220  may be represented by first fan speed  110  of  FIG. 1 . 
   As shown in  FIG. 2 , temperature inputs may be fed to fan controller  210  for monitoring temperatures within a system (e.g., for which fan  220  provides heat dissipation). As such, fan controller  210  may then control the speed of fan  220  to respond to changes in the system temperature, where the temperature input may comprise one or more temperatures from various locations within the system. For example, if fan controller  210  detects a rise in system temperature at one or more locations, then the speed of fan  220  may be increased to reduce the system temperature to an acceptable level. The properties of the control system implemented by fan controller  210  may be preconfigured (e.g., by a user, during manufacture, etc.), where control system parameters may be stored in a memory coupled to or integrated within fan controller  210 . Alternatively, the control system may be dynamically configured on-the-fly by a system coupled to or integrated within fan controller  210 . 
   Alert signals may also be input to fan controller  210  (e.g., for monitoring faults associated with a system, etc.). The alert signals may be associated with one or more components of the system (e.g., ethernet hardware, power supply, etc.) and indicate a condition warranting attention (e.g., battery low, power failure, component failure, overheated component, required system reboot, etc.). Alternatively, the alert signal may be that which is optionally routed to a light-producing device, speaker, etc. of the system. As such, fan controller  210  may be integrated in place of or in conjunction with existing hardware. 
   Upon detecting a request for an alert, fan controller  210  may control the speed of fan  220  to produce an audible alert generated by a differential in speed of fan  220  with respect to fan  230  (e.g., as discussed above with respect to  FIG. 1 ). Fan  230  may be driven at a substantially-constant speed (e.g.,  120  of  FIG. 1 ) in proximity to fan  220  such that the speed of fan  220  (e.g.,  110  of  FIG. 1 ) may be varied to change the magnitude of the fan speed differential, thereby changing the frequency and intensity of the fan interference sound (e.g., as discussed above with respect to  FIG. 1 ). As such, the fan controller  210  may control the frequency and intensity of the fan interference sound to produce an alert comprising speech, music, a siren, or the like. Thus, an alert may be detected above ambient room noise and more clearly identify one or more systems to which a fault pertains, thereby providing enhanced fault notification and/or isolation using existing system hardware to reduce cost. 
   Although  FIG. 2  shows only one fan (e.g.,  220 ) coupled to fan controller  210 , it should be appreciated that more than two fans may be coupled to fan controller  210  for control thereof in other embodiments. Additionally, although fan  230  has been described as being spun at a substantially-constant speed to simplify the discussion, it should be appreciated that speed of fan  230  may be varied in other embodiments. 
     FIG. 3  shows block diagram  300  of an exemplary fan controller in accordance with one embodiment of the present invention. As shown in FIG.  3 , fan controller  210  is coupled to fan  220  for controlling its speed in response to temperature and/or alert input signals fed into input interface  310 . Signals input via input interface  310  may be conveyed to processor  320  for processing. As such, fan controller may monitor temperatures and alerts as discussed above with respect to  FIG. 2 . 
   Upon accessing a temperature signal from input interface  310 , processor  320  may determine a temperature associated with the system and also whether additional airflow is required based upon the determined temperature. If additional airflow is needed, processor  320  may send a signal to fan speed control  330  to increase the speed of fan  220 . Fan speed control  330  may control fan  220  using a pulse width modulation (PWM) signal, analog signal, or the like, and may receive fan speed information (e.g., a digital or analog signal indicating revolutions per minute, a voltage proportional to its speed, etc.) from fan  220 , a tachometer (not shown) coupled to processor  320 , or the like. Alternatively, if it is determined that a received temperature has been reduced to an acceptable level, processor  320  may instruct fan speed control  330  to reduce the speed of fan  220 . As such, fan speed controller  210  may be used to set a baseline fan speed such that system temperatures are maintained at a given level, where the control system properties may be either preconfigured or dynamically configured on-the-fly as discussed above with respect to  FIG. 2 . Additionally, control system parameters may be stored within memory  350  (e.g., for access by processor  320 ). 
   Upon accessing an alert input signal from input interface  310 , processor  320  may determine the nature of the alert (e.g., to which portions of the system it pertains). Thereafter, processor  320  may access alert information  340  from coupled memory  350 , where alert information may comprise information (e.g., data, instructions, etc.) relevant to the requested alert that processor  320  may use to implement an audible alert. For example, alert information  340  may comprise fan speed information required to implement a given siren, speech or other alert. Alternatively, alert information  340  may comprise frequency information that processor  320  may use to derive fan speed information for implementing the siren, speech or other alert. As such, once fan speed information is obtained from the relevant alert information (e.g.,  340 ), processor  320  may instruct fan speed control  330  to adjust the speed accordingly (e.g., using fan speed feedback as discussed above) to implement the alert by varying the frequency and/or intensity of the fan interference sounds. 
   Processor  320  may perform frequency calibration using frequency detector  360 , where frequency detector  360  is capable of measuring a frequency and/or intensity of sound. Frequency detector  360  may comprise a microphone, or alternatively, may comprise a microphone and one or more signal processing components required to measure the frequency and/or intensity of sound. Frequency calibration may be used to determine a fan speed (e.g., of fan  220 ) required to produce a given frequency when the speed of a second fan (e.g.,  230 ) is unknown. Alternatively, frequency calibration may be used to fine-tune a system for which fan speeds are known or reasonably approximated. As such, processor  320  may vary the speed of fan  220  until a desired frequency is produced, where the frequency is determined by processor  320  based upon input from frequency detector  360 . By more accurately determining a fan speed for which a given frequency is produced, processor  320  may more accurately implement a given alert for which fan speed or frequency information (e.g., alert information  340 ) is available (e.g., within memory  350 ). 
   As shown in  FIG. 3 , fan speed controller  210  may be implemented using a programmable system on a chip (PSOC) microcontroller. As such, input interface  310  may be implemented using one or more PSOC ports (e.g., digital input/output, analog input/output, etc.), which are coupled to a PSOC core implementing processor  320 . Memory  350  may be implemented using one or more memories (e.g., SRAM, SROM, flash, etc.) coupled to the core. Frequency detector  360  and fan speed control  330  may be implemented as PSOC peripherals using one or more digital and/or analog blocks, where the peripherals may also utilize various PSOC system resources to perform frequency detection and fan speed control operations. Additionally, control system parameters for configuring fan controller  210  may be input via one or more system resources (e.g., I2C, etc.), where configuration may be performed manually (e.g., by a user) or dynamically (e.g., by another system, device, component, etc.) via a host coupled to the PSOC. 
   Although  FIG. 3  shows only one fan coupled to fan controller  210 , it should be appreciated that multiple fans may be coupled to fan controller  210  in other embodiments. Additionally, more than one fan may be coupled to fan speed control in other embodiments. Further, although  FIG. 3  shows only one fan speed control (e.g.,  330 ), it should be understood that fan controller  210  may comprise more than one fan speed control in other embodiments. As such, each fan speed control component may be coupled to one or more fans. Alternatively, one or more of the fan speed control components may be unused and not coupled to any fans. 
     FIG. 4  shows exemplary fan speed graph  400  of two variable-speed fans in accordance with one embodiment of the present invention. As shown in  FIG. 4 , a first fan speed  110  and second fan speed  420  are graphed with respect to time, similar to the fan speeds graphed in graph  100  of  FIG. 1 . However, whereas second fan speed  120  of  FIG. 1  represented a fan spinning at a substantially-constant speed, second fan speed  420  represents a variable-speed fan similar to first fan speed  110 . As such, a variation of either fan speed with respect to the other creates fan speed differentials (e.g., first fan speed differential  430  and second fan speed differential  440 ), where the differential between the two fan speeds may vary with respect to time. For example, first fan speed differential  430  is larger than second fan speed differential  440 . 
   As discussed above with respect to  FIG. 1 , the magnitude of the fan speed differential may change the frequency of the resulting fan interference sounds (e.g., to implement alert notifications, etc.). Also, a variation in the average fan speed may create a change in intensity of the fan noise as discussed above with respect to  FIG. 1 . However, given that both fan speeds (e.g.,  110  and  420 ) are variable as depicted in graph  400 , a change in the magnitude of the fan speed differential may be controlled by changing the speed of either fan. As such, a fan speed controller may vary the speed of either fan, simultaneously or individually, to change the frequency and/or intensity of the fan interference noise. Additionally, the fans whose speeds are represented in  FIG. 4  may be located with the same system, within different systems located near enough to produce an audible fan interference sound. Alternatively, at least one fan may be located outside a system. 
   Although  FIG. 4  depicts a specific relationship between the speeds of two fans, it should be appreciated that the two fan speeds may be alternatively represented in other embodiments. For example, first fan speed  110  and/or second fan speed  420  may be alternatively varied, or in another embodiment, may comprise a combination of constant and varying periods. Additionally, although  FIG. 4  depicts a change in the magnitude of a fan speed differential for only two fans, it should be appreciated that more than two fans may produce fan interference sounds in other embodiments. As such, one or more fan interference sounds may co-exist based on one or more fan speed differentials. Thus, a resultant frequency and/or intensity of the fan interference sound may be based on a combination of multiple fan interference sounds. 
     FIG. 5  shows block diagram  500  of an exemplary fan controller coupled to multiple fans in accordance with one embodiment of the present invention. As shown in  FIG. 5 , fan controller  210  is coupled to fan  220  and fan  230  for controlling the speed of the fans (e.g., first fan speed  110  and second fan speed  420 ) in response to temperature and/or alert inputs. As such, fan controller  210  may use two fans to regulate system temperature (e.g., by adjusting the baseline fan speed, etc.), and also vary the magnitude of the fan speed differential (e.g.,  430 ,  440 , etc.) to implement audible alerts or notifications as discussed above (e.g., with respect to  FIGS. 1 ,  2 ,  3  and  4 ). Alternatively, where fan controller  210  is coupled to more than two fans in other embodiments, fan controller  210  may perform such operations by controlling more than two fans. 
     FIG. 6  shows block diagram  600  of an exemplary fan controller coupled to multiple fans with external fan speed controls in accordance with one embodiment of the present invention. As shown in  FIG. 6 , fan controller  610  is coupled to separate external fan speed controls  330   a  and  330   b , where the combination of fan speed controller  610  and external speed controls  330   a  and  330   b  may operate analogously to fan controller  210  with internal fan speed controls (e.g.,  330 ). As such, in response to receiving temperature and/or alert inputs, fan controller  610  may regulate system temperature (e.g., by adjusting the baseline fan speed, etc.), and also vary the magnitude of the fan speed differential (e.g.,  430 ,  440 , etc.) to implement audible alerts as discussed above (e.g., with respect to  FIGS. 1 ,  2 ,  3 ,  4  and  5 ). For example, fan speed control  330   a  is operable to control the speed of coupled fan  220  in response to control signals sent from fan controller  610 . Similarly, fan speed control  330   b  is operable to control the speed of coupled fan  230  in response to control signals sent from fan controller  610 . Upon receiving control signals from fan controller  610 , fan speed control  330   a  and/or  330   b  may vary the speed of a coupled fan (e.g.,  220  and/or  230 ) by generating a PWM signal, analog signal, or the like (e.g., as discussed above with respect to  FIG. 3 ). 
   Although fan controller  610  is shown coupled to two fans in  FIG. 6 , it should be appreciated that fan controller  610  may control more than two fans in other embodiments. Additionally, fan controller  610  may utilize all internal fan speed controls (e.g.,  330 ), all external fan speed controls (e.g.,  330   a ,  330   b , etc.), or a combination of internal and external fan speed controls to control coupled fans. 
     FIG. 7  shows block diagram  700  of an exemplary fan controller coupled to multiple fans with external and internal fan speed controls in accordance with one embodiment of the present invention. As shown in  FIG. 7 , fan controller  710  may control coupled fans  220  and  230  analogously to fan controller  610 , except that fan controller  710  uses a combination of internal and external fan speed controls to control coupled fans. As such, in response to receiving temperature and/or alert inputs, fan controller  710  may regulate system temperature (e.g., by adjusting the baseline fan speed, etc.), and also vary the magnitude of the fan speed differential (e.g.,  430 ,  440 , etc.) to implement audible alerts as discussed above (e.g., with respect to  FIGS. 1 ,  2 ,  3 ,  4 ,  5  and  6 ). For example, fan speed control  330   a  is operable to control the speed of coupled fan  220  (e.g., using PWM signals, analog signals, etc.) in response to control signals sent from fan controller  710 . However, fan  230  may be directly controlled by fan controller  710  (e.g., by use of internal fan speed control  330 ), where fan controller  710  may control the speed of fan  230  by varying a PWM signal, analog signal, or the like. 
   Although fan controller  710  is shown coupled to two fans in  FIG. 7 , it should be appreciated that fan controller  710  may control more than two fans in other embodiments. Additionally, fan controller  710  may utilize all internal fan speed controls (e.g.,  330 ), all external fan speed controls (e.g.,  330   a ,  330   b , etc.), or a combination of internal and external fan speed controls to control coupled fans. 
     FIG. 8  shows process  800  for enhanced alert notification in accordance with one embodiment of the present invention. As shown in  FIG. 8 , step  810  involves accessing temperature measurement signals. The temperature measurement signals may be accessed by a fan controller (e.g.,  210 ,  610 ,  710 , etc.), and may represent temperatures within one or more locations of a single system or multiple systems. Additionally, the temperature measurement signals may be associated with a system or systems for which fans controlled by the fan controller may provide heat dissipation. 
   After accessing the temperature measurement signals, a fan speed baseline may be updated in step  820  based upon the measured temperatures. The fan speed baseline may represent an average fan speed for one or more fans controlled by a fan controller (e.g.,  210 ,  610 ,  710 , etc.) to provide sufficient cooling for a system or systems (e.g., for which fans controlled by the fan controller provide heat dissipation). As such, an increase in a system temperature may indicate a need to raise the fan speed baseline to provide additional heat dissipation, thereby lowering the system temperature. Conversely, a decrease in a system temperature may indicate a need to lower the fan speed baseline to reduce heat dissipation, thereby raising the system temperature. 
   As shown in  FIG. 8 , a determination is made in step  830  as to whether an alert is requested. An alert request may be detected by monitoring an alert input signal, where an alert input may identify a fault present in one or more components (e.g., ethernet hardware, power supply, etc.) of one or more systems (e.g., for which the fan speed baseline is updated in step  820 ) and indicate a condition warranting attention (e.g., component failure, overheated component, required system reboot, etc.). Alternatively, the alert signal may be that which is optionally routed to a light-producing device, speaker, etc. of the system. If an alert is not requested in step  830 , then steps  810  and  820  may be repeated. Alternatively, if an alert is requested in step  830 , then step  840  may be performed. 
   Step  840  involves making a determination as to whether multiple fans are present to generate fan interference sounds. Multiple fans may be present within the same system, where the presence of the fans may be detected by accessing data stored within a system (e.g., in a coupled memory), performing inter-system communication (e.g., a fan presence check performed by a fan controller), etc. Alternatively, the presence of a fan outside a given system (e.g., not accessible by a given fan controller, used for HVAC, etc.) may be detected by varying the speed of a system fan over a given rotational speed range and simultaneously monitoring the frequency (e.g., using frequency detector  360 ) of any resulting fan interference sound. If a fan interference sound is detected, then the presence of at least one non-system fan may be identified. Accordingly, if an additional system or non-system fan enabling the generation of fan interference sounds is not detected in step  840 , then steps  810  through  830  may be repeated. Alternatively, if an additional fan is detected such that fan interference sounds may be generated, then step  850  may be performed. 
   As shown in  FIG. 8 , step  850  involves performing frequency calibration. Frequency calibration may be used to determine a fan speed (e.g., of fan  220 ) required to produce a given frequency when the speed of a second fan (e.g.,  230 ) is unknown. Alternatively, frequency calibration may be used to fine-tune a system for which fan speeds are known or reasonably approximated (e.g., where the fans are both controlled by the same fan controller). As such, a fan controller may vary the speed of a coupled fan until a desired frequency is produced, where the frequency is determined by one or more components (e.g., frequency detector  360 ) coupled to or integrated within the fan controller. Additionally, frequency calibration may be performed for multiple frequencies and fan speeds such that accuracy is improved. 
   Step  860  involves accessing alert information associated with an alert requested in step  830 . The alert information (e.g.,  340  of  FIG. 3 ) may be accessed from a memory (e.g.,  350  of  FIG. 3 ) coupled to or integrated within a fan speed controller (e.g.,  210 ,  610 ,  710 , etc.). Additionally, the alert information may comprise information (e.g., data, instructions, etc.) relevant to the requested alert that may be used to implement an audible alert. For example, the alert information may comprise fan speed information required to implement a given siren, speech or other alert. Alternatively, the alert information may comprise frequency information that may be used to derive fan speed information for implementing the siren, speech or other alert. 
   Once the relevant alert information is accessed, the requested alert may be implemented in step  870  by varying the fan speed accordingly (e.g., in accordance with fan speed information associated with the alert information). A fan controller (e.g.,  210 ,  610 ,  710 , etc.) may vary the speed of the fan in accordance with the fan speed information (e.g., using fan speed feedback as discussed above with respect to  FIG. 3 ), thereby varying the frequency and/or intensity of the fan interference sounds to implement the audible alert. Thereafter, steps  810  through  860  may be repeated to detect and correct for any undesirable change in temperature (e.g., resulting from implementing the alert, from a change in heat dissipation by one or more system components, etc.), and also to detect any requested alerts for which an audible alert may be implemented using fan interference sounds. 
   In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Thus, the sole and exclusive indicator of what is, and is intended by the applicant to be, the invention is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Hence, no limitation, element, property, feature, advantage, or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.