Abstract:
A device is provided which allows a personal computer user to monitor the operational parameters of the central processing unit&#39;s cooling fan. This device, called the CPU cooling fan speed monitor, characterizes the normal operating speed range of the CPU fan and the fan speed and provides warnings of improper fan speed. The fan speed monitor is a microcontroller-based device which has two principle modes of operation: the characterization mode; and the monitor mode. In the characterization mode, the fan speed monitor determines the “normal” operating speed range of the cooling fan. In the monitor mode, the fan speed monitor provides audible and visual indication of the operating speed of the CPU cooling fan.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an improvement in the design of the cooling fan used in personal computers (herein after, PC) today to cool the central processing unit (herein after, CPU). More specifically, to the use of a fan speed monitor which constantly checks the rotational speed of the cooling fan and which will provide warnings of any improper operational variances. 
     A CPU cooling fan maintains the temperature of the CPU within safe limits. If the rotational speed of the fan slows to below a minimum value the CPU will overheat. A fan running at speeds in excess of a maximum value may indicate an impending fan failure which will lead to the overheating of the CPU. The result of overheating the CPU on the operation of the PC is unpredictable and often times will cause errors in the operation of the PC which may lead the user to blame bugs in the software. In certain systems fan failures or anomalies may even lead to permanent damage of the CPU. As system CPU&#39;s and the design of the fan or heat sinks used on the CPU can vary greatly, the minimum safe speed of the cooling fan may also vary on the make and model of the PC being used. 
     Current CPU fan detectors either operate on detecting the CPU temperature or on controlling the cooling fan speed and provide an indication of cooling fan failure after it has failed or the temperature of the CPU is too high. This is clearly an undesirable situation and some form of early detection of eminent cooling fan failure is needed. 
     Additionally, available CPU fan operation detectors do not have memory, which means that they can only indicate the current operating conditions of the cooling fan. This means that if the fan momentarily fails, for however long, and self corrects, this condition is not recognized by the operator unless he is present during this failure. This is also an undesirable situation and a system with memory which will alert the operator of such intermittent failures is needed. 
     SUMMARY OF THE INVENTION 
     It is the primary objective of the present invention to provide a method of monitoring the operation of a CPU cooling fan at all times that a PC is running. 
     It is an additional objective of the present invention to provide such a method which will warn a PC user of variances in the operation of the cooling fan. 
     It is still a further objective of the present invention to provide such a method of warning a PC user of such occurrences that contains a memory feature that will keep track of cooling fan variances which will enable a user to be aware of them whether or not they are using the machine during the time of the fan variance. 
     These objectives are accomplished by the use of a cooling fan monitor which provides an early warning of impending fan failure. The fan monitor is microprocessor based and has two operating modes: the characterization mode; and the monitor mode. When the present device is first used it will be in the characterization mode. In this mode data is gathered about the operating characteristics of the CPU fan. In the characterization mode, the microcontroller detects the normal operating range of the CPU fan, which is in general PC dependent. The fan speed monitor saves this information in nonvolatile memory for use during the monitor mode. Typically the cooling fan monitor will be left in the characterization mode for sufficent length of time to allow data to be gathered in both high use and low use time periods. The cooling fan monitor is then manually switched, by depressing a button, to the monitor mode. In the monitor mode, the fan speed monitor indicates whether the CPU cooling fan is operating within its normal operating range or if it is operating outside of this range. If the CPU cooling fan goes outside of this normal operating range, the fan speed monitor remembers this condition and indicates the anomaly until it is reset by the operator. This anomaly may be transmitted by various indicators depending upon the severity of the anomaly. This is typically done by setting given ranges. For example Range A might be reached when ever the fan speed varies by a factor of 10%, Range B may be reached when the fan speed varies by 20%. As higher ranges are reached different levels of of severity may be indicated to user, these ranges may vary greatly depending upon a particular users needs and system tolerance. If power is interrupted to the system, the cooling fan monitor will retain its current state thus, when the power resumes the monitor will resume in the state it was in at the time of the power outage. 
     The fan speed monitor determines the CPU cooling fan speed by monitoring current glitches (which are a function of rotational fan speed) in the fan current. The glitches interrupt the microcontroller which counts the number of such glitches over a specified period of time to determine the rotational fan speed. The fan current is converted to a voltage by passing it through a resistor in series with the fan. Thus, the current glitches are detected as voltage glitches. These voltage glitches are passed through a comparator circuit, which in turn interrupts the processor. 
     The present invention is equipped with a series of indicator lights and an audible annunciator which convey the information gathered by the fan speed monitor to the PC user. The speed visual indicators may be red, yellow, and green and indicate the current and past speed of the fan motor since the fan speed monitor was last reset. The operation of the indicator lights and audible annunciator may be typically as follows: 
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 State Table for the Fan Speed Monitor 
               
             
          
           
               
                 State 
                 Red 
                 Yellow 
                 Green 
                 Annunciator 
               
               
                   
               
               
                 Normal Speed (NS) 
                 off 
                 off 
                 on 
                 off 
               
               
                 Range - A (RA) 
                 off 
                 on 
                 off 
                 audio on/off 
               
               
                 Range - B (RB) 
                 on 
                 off 
                 off 
                 on 
               
               
                 NS was in RA 
                 off 
                 blinking 
                 on 
                 off 
               
               
                 NS was in RB 
                 blinking 
                 off 
                 on 
                 off 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Mode Switch functions for the Fan Speed Monitor 
               
             
          
           
               
                   
                 Description 
                 Mode Switch 
                 Indicators 
               
               
                   
                   
               
               
                   
                 CM → MM 
                 Press switch for 10 sec. 
                 Cycle: R → Y → G 
               
               
                   
                 MM → CM 
                 Press switch for 10 sec. 
                 See State Table 
               
               
                   
                 Reset 
                 Press switch for 1 sec. 
                 See State Table 
               
               
                   
                   
               
               
                   
                 CM = Characterization Mode  
               
               
                   
                 MM = Monitor Mode  
               
             
          
         
       
     
     For a better understanding of the present invention reference should be made to the drawings and the description in which there are illustrated and described preferred embodiments of the present invention. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of the present invention illustrating the manner in which its components work with the microcontroller to monitor and indicate the speed of the CPU cooling fan. 
     FIG. 2 is a schematic diagram for the microprocessor interrupt signal component of the present invention which is used to determine the CPU cooling fan rotational speed. 
     FIG  3  is a schematic diagram for the fan rotational speed visual indicators components of the present invention which convey the state of the cooling fan to the user. 
     FIG. 4 is a schematic diagram for the nonvolatile memory component of the present invention which is used to store fan speed characterization data. 
     FIG. 5 is a schematic diagram for the audible annunciator component of the present invention. 
     FIG. 6 is a schematic diagram for the mode/reset switch component of the present invention. 
     FIG. 7 is a detail diagram of the microcontroller component of the present invention. 
     FIG. 8 is an illustration of the control panel of the CPU cooling fan speed monitor. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, and more specifically to FIG. 1, the CPU cooling fan speed monitor  10  as illustrated by the block diagram of this Figure is made up of six (6) major parts: the fan speed interrupt  12 ; the visual indicators  14 ; the nonvolatile memory  16 ; the audible indicators  18 ; the mode/reset switch  20 ; and the microcontroller  22 . This figure illustrates the manner in which the fan speed interrupt  12 , the nonvolatile memory  16 , and the mode/reset switch  20  transfer information to the microcontroller  22  which in turn processes this information and passes the pertinent processed information to the visual indicators  14  and the audible indicators  18 . This configuration provides the PC user with an accurate picture of the state of the CPU cooling fan  24  both during the use of the machine and during periods when the PC was left running but may not have been consistently monitored by an operator. 
     The construction of each of the major components of the present invention is further detailed in the additional Figures following FIG.  1 . FIG. 2 illustrates the method employed to construct the fan speed interrupt circuit  12 . FIG. 3 illustrates the method employed to construct the visual indicators  14  which are used to display to the PC user the current state of the CPU cooling fan  24  speed. FIG. 4 illustrates the method employed to construct the nonvolatile memory  16  which is used to store fan speed characterization data and the current state of the CPU cooling fan  24  speed. FIG. 5 illustrates the method employed to construct the audible indicator  18  which is used to alert the PC user of a fan speed fault. FIG. 6 illustrates the method employed to construct the mode/reset switch  20  which is used to change the modes of operation of the present invention. FIG. 7 illustrates the method employed to construct the microcontroller  22  which is used to control the functioning process of the invention. 
     As previously stated, the method of construction and the operation of the fan speed interrupt circuit  12  are illustrated in FIG.  2 . The fan speed interrupt circuit  12  converts current glitches in the DC current to the CPU cooling fan  24 . These current glitches are directly proportional to the rotational speed of the cooling fan  24 . The resistor  26 , which is located in line between the cooling fan  24  and the voltage comparator  34 , is used to convert the fan current glitches to voltage glitches. The DC offset components  28 , which are located in line between the resistor  26  and the voltage comparator  34 , are used to add a DC offset appearing across the resistor  26  (this occurrence will be referred to as V+). The DC blocking capacitor  30 , located in line between the resistor  26  and the DC offset components  28 , is used to couple the voltage developed across the resistor  26  to the DC voltage across the DC offset components  28 . The DC voltage referencer  32 , located in line between the DC offset components  28  and the voltage comparator  34 , provide as voltage reference to the voltage comparator  34  (this will be referred to as V−). The voltage comparator  34  compares the V+ to the V− and produces short duration voltage pulses (compatible with the microcontroller  22  logic levels) which are used to interrupt the microcontroller  22 . This information is passed from the voltage comparator  34  to the microcontroller  22  through the fan interrupt input/output port  35 . The microcontroller  22  counts these voltage pulses over a fixed period of time interval to obtain a measurement which is proportional to the rotational speed of the CPU cooling fan  24 . 
     The manner of construction and the method of operation of the visual indicator  14  component of the present invention are detailed in FIG.  3 . The visual indicator  14  is the component of the invention which conveys a visual signal to the operator of a PC which illustrates the operating status of the CPU cooling fan  24 . The visual indicator  14  operates by the use of a plurality of indicator lights: the red indicator light  38 ; the yellow indicator light  40 ; and the green indicator light  42 . These indicator lights are connected to the microcontroller  22  by the use of the three light electrical leads  36  which transfer the data processed in the microcontroller  22  through the indicator light input/output ports  37 . Each of the indicator light circuits has a current limiting resistor  63  which terminate at the grounds  62  to complete the individual circuits. 
     The manner of construction and the method of operation of the nonvolatile memory circuit  16  are illustrated in FIG.  4 . The nonvolatile memory circuit  16  is a serial electrically erasable programmable read only memory (EEPROM)  45  which retains the data programed into it even during power outages. This ensures that the data is safe guarded in the event that the electrical power to the circuit is lost for any reason. 
     This component of the present invention is also equipped with a plurality of passive pull-up resistors  44  which function for the open drain transistors (not shown) on the microcontroller  22 . 
     The nonvolatile memory  16  is connected to the serial clock  46  through the serial clock input/output port  47  of the microcontroller  22  by the use of the serial clock feed line  48 . The serial clock  46  provides the signal to clock the data into the serial EEPROM  45  where the data is retained. 
     Finally, the nonvolatile memory is also connected to serial data  50  through the serial data input/output port  51  of the microcontroller  22  by the use of the serial data feed line  52 . The serial data input/output port  51  serves to provide the data programed into the serial EEPROM  45  and read from the serial EEPROM  45 . 
     The manner of construction for the audible indicator  18  is illustrated in FIG.  5 . The audible indicator  18  is the component of the present invention which supplies an audible warning of CPU cooling fan  24  problems to the user of the PC. The major component of the audible indicator  18  is the annunciator  54  which supplies the audible signal and can be made of a speaker, buzzer, or other similar device. The electrical current necessary to operate the annunciator  54  is supplied by the current drive  56  which is connected to the current drive input/output port  57  of the microcontroller  22  by the means of the current drive feed line  58 . Additionally, there is a current limit resistor  60  in the current drive feed line  58  between the microcontroller  22  and the current drive  56  which provides the necessary drive current for the annunciator  54 . 
     The manner of construction of the mode/reset switch  20  is illustrated in FIG.  6 . The mode/reset switch is the component of the present invention which allows an operator of a PC to reset the system after it has detected an operating error in the CPU cooling fan  22 . The mode/reset switch  20  is a normally open push-button switch. When the mode/reset switch  20  is open, the microcontroller  22  receives a logic- 1  (high voltage) at its switch input port  64  by means of the switch feed line  65  through the passive pull-up resistor  44 . Conversely, when the mode/reset switch  20  is closed, the microcontroller  22  receives a logic- 0  (low voltage) at its switch input port  64  by means of the switch feed line  65  through the passive pull-up resistors  44 . This operates to provide the requisite logic states for the microcontroller  22 . 
     The construction of the microcontroller  22  is illustrated in FIG.  7 . The microcontroller  22  contains all of the input/output ports, interval timers, program and data memory, and interrupt control circuitry on a single monolithic integrated circuit. The microcontroller  22  is also equipped with a instruction cycle timer  66  which controls the cycle time of the microcontroller  22 . Additionally, this figure also illustrates the manner in which the other components of the invention are connected to the microcontroller  22  to both receive raw information and transmit processed information to these other components. 
     Finally, FIG. 8 is an illustration of the control panel  68  of the CPU cooling fan Speed monitor  10 . The control panel  68  houses the mode/reset switch  20 , the annunciator  54  of the audible indicator  18 , and the red, yellow, and green indicator lights,  38 ,  40  and  42 , of the visual indicator  14 . The control panel  68  functions as the point at which the controls and indicator systems are mounted to give the operator the necessary feedback. 
     Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible for example the indicator means and programming of the normal operating windows could vary greatly, Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.