Abstract:
An automated beverage brewing system includes a liquid storage tank and a metering chamber. The metering chamber is at least partially submerged beneath a standing level of liquid in the storage tank. The chamber includes a sealable liquid inlet port communicating with the interior of the storage tank beneath the standing level of liquid. The chamber also includes a liquid outlet port and an aperture that receives compressed air, wherein the compressed air forces liquid from the liquid output port of the chamber for use in preparing a brewed beverage. A pump provides the compressed air and a controller monitors a pressure signal value indicative of the air pressure in the metering chamber. The controller commands the pump on to commence flow of liquid from the metering chamber. The controller then commands the pump off several seconds after detecting a drop in air pressure within the chamber. A baffle is affixed to the distal end of a shaft, which is moved between a first and second position. In the second position the baffle seals a section of the storage tank to form the metering chamber. The system may also include a second brew pump that allows a user to customize the quantity of liquid delivered from the brewing system for a stronger brewed beverage.

Description:
PRIORITY INFORMATION 
     This application claims priority from a provisional application filed Apr. 18, 2001 designated Ser. No. 60/284,454 entitled “System for Monitoring and Controlling the Operation of a Single Serve Beverage Brewer”. This application is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to beverage dispensing and brewing systems, and in particular with a system for monitoring and controlling a beverage brewer. 
     Many different coffee brewing systems have been designed. Most utilize a pump, such as a peristaltic pump, to transfer water from a reservoir through a conduit to a brewing chamber. The pump is turned on at the beginning of a brewing cycle and at the end of a specific time period the pump is turned off. Other brewing systems use an electrically controlled device to open a valve at the bottom of a reservoir. Through gravity the water travels through a conduit to a brewing chamber. Again at the end of a specific time period, the valve is closed. These prior brewing systems lack the capability of consistently dispensing equal volumes of liquid. The systems are dependent on the accuracy of the timers, the pressure of the liquid, etc. 
     Therefore, there is a need for an automated beverage brewing system for dispensing a predetermined volume of liquid from a storage tank. 
     SUMMARY OF THE INVENTION 
     Briefly, according to an aspect of the present invention, a beverage brewing system uses compressed air to drive liquid from a metering chamber for use in preparing a brewed beverage. 
     An automated beverage brewing system receives a cartridge containing a beverage extract and establishes a liquid flow path through the cartridge to provide a brewed beverage. The system includes a holder that holds and pierces the cartridge to provide a cartridge inlet and a cartridge outlet that together establish a flow path through the beverage extract to provide the brewed beverage. A storage tank comprising a supply of liquid and having a reduced diameter cup-shaped bottom is in fluid communication with the cartridge via a chamber outlet port. A portion of the storage tank is controllably sealed to form a metering chamber in cooperation with the reduced diameter cup-shaped bottom. A first pump provides compressed air along a flow line to the metering chamber to force liquid from the metering chamber and through the chamber outlet port. A sensor senses pressure in the flow line and provides a sensed pressure signal indicative thereof. A controller commands the first pump on, monitors the sensed pressure signal and turns the first pump off after detecting that the sensed pressure signal value has dropped below a threshold value indicating the predetermined volume of liquid has been delivered through the chamber outlet port. 
     The system may also include a second air pump that delivers a second flow of compressed air downstream of the metering chamber outlet port and upstream of the cartridge inlet in response to a brew interrupt signal received by the controller to drive the liquid downstream of the metering chamber outlet port to the cartridge. Advantageously, this allows a user to control the strength of their brewed beverage by using less water than the nominal amount dispensed by the brewer when the brew interrupt bottom is not depressed during a brew cycle. 
     These and other objects, features and advantages of the present invention will become apparent in light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a vertical sectional view taken through a single serve beverage brewer; 
     FIGS. 2A-2C are enlarged views showing the illuminated liquid level indicator; 
     FIG. 3 is a control schematic; 
     FIG. 4 is a flow chart generally depicting the sequential steps in a brew cycle; 
     FIG. 5 is a vertical sectional view taken through an alternative embodiment single serve beverage brewer; 
     FIG. 6 is a block diagram illustration of the control system associated with the brewer illustrated in FIG. 5; 
     FIGS. 7A and 7B are flow charts that together illustrate steps performed by the controller of FIG. 6; 
     FIG. 8 is a flow chart illustration of steps performed by the controller of FIG. 6 to control a interrupt brew pump illustrated in FIG. 5; and 
     FIG. 9 is a flow chart illustration of a built-in-test (BIT) routine performed by the controller of FIG. 6 to detect faults in the brewer illustrated in FIG. 5; 
     FIG. 10 is a flow chart illustration of a routine for controlling the liquid heater; and 
     FIG. 11 is a flow chart illustration of a routine for monitoring the liquid level within the storage tank of the brewer illustrated in FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is specially adapted for use in, although not limited in application to, a brewing system  10  illustrated in FIG.  1 . Here, the dispensed liquid is water that is heated to a predetermined elevated temperature to brew beverages from extracts (e.g., coffee, tea, powders and concentrates) contained in disposable hermetically sealed cartridges. 
     With reference initially to FIG. 1, a single serve brewer  10  includes a housing  12  containing a liquid storage tank  14 . The tank has a lower metering chamber  16  formed by a reduced diameter cup-shaped bottom  18  integrally joined to the larger diameter tank side wall at a circular sealing surface defining a seat  20 . Water can be poured into the storage tank  14  via an inlet  17 . 
     A fixed internal structure includes a horizontal platform  22  and struts  24  supporting a vertically disposed sleeve bearing  26  aligned centrally with respect to the tank  14  and its cup-shaped bottom  18 . 
     A vertically reciprocal shaft  28  extends through the sleeve bearing  26 . The shaft carries a generally conically shaped baffle  70  at its lower end, and a circular plate  32  disposed beneath the platform  22 . A resilient and compressible circular gasket  33  on the lower surface of the baffle overlies the seat  20 . 
     An arm  34  is pivotally mounted on a bracket  36  carried by the platform  22 . The arm  34  is connected to the shaft  28  by a pin  38 . A coiled spring  40  surrounds the pin  38  between the arm  34  and the upper surface of platform  22 , and an inflatable bladder  42  is positioned between the bottom surface of the platform  22  and the plate  32 . 
     The distal end of the arm  34  extends into a brewing chamber  44  designed to accept a single serve beverage filter cartridge  46  of the type for example described in co-pending patent application Ser. No. 09/782,622 filed Feb. 13, 2001, the description of which is herein incorporated by reference in its entirety. 
     An air pump  48  on the platform  22  is pneumatically connected to the bladder  42 , and is also connected via a flexible hose  50  to a port  52  in the baffle  70 . A metering tube  54  extends through the baffle  70  into the chamber  16 . The metering tube  54  is connected via a second flexible hose  56  to a depending tubular probe  58  carried by the arm  34 . A second tubular probe  60  underlies the cartridge  46  and opens downwardly above an exterior shelf  62  configured and dimensioned to support a cup  64  or other like receptacle. 
     The tank  14  stores a supply of liquid  66  heated by an electrical heating element  68  underlying the cup-shaped bottom  18 . 
     A tubular transparent column  72  is connected by upper and lower branch conduits  74  and  76  to the tank  14 . As can best be seen by further reference to FIGS. 2A-2C, the column is illuminated from below by a blue light source  78 , such as a light emitting diode (LED). The column  72  contains liquid at the same level as the liquid level in tank  14 . A ball  80  is buoyantly supported on the surface of the liquid contained in column  72 , and its position in the column is visually enhanced by light emitted from the underlying light source  78 . Optical sensors  82 ,  84  are positioned to sense the position of the ball in its uppermost and lowermost positions, as shown in FIGS. 2B and 2C. The uppermost position provides an indication that the tank  14  is filled, and the lowermost position conversely indicates that the tank has been emptied and is in need of being refilled. 
     With reference to FIG. 3, it will be seen that the sensors  82 ,  84  provide output signals to a controller  86 . 
     Referring again to FIG. 1, the brew chamber  44  includes a drawer  88  that may be opened to the position indicated by the broken lines in FIG. 1 in order to accept the filter cartridge  46 . The drawer  88  is carried on a slide bar  90  guided by rollers  92 , and a switch  94  provides a control signal to the controller  86  (FIG. 3) indicating open and closed drawer positions. 
     A temperature sensor  96  provides a signal to the controller  86  (FIG. 3) indicative of liquid temperature in the metering chamber  16 , and a pressure sensor  98  provides a signal to the controller indicative of air pressure in the hose  50 , which is representative of the air pressure in the metering chamber  16 . 
     Referring again to FIG. 3, a panel  100  on the brewer head includes red and green indicator lights  102   a ,  102   b , connected to the controller  86 . The heater  68  and pump  48  are also connected to the controller  86 . 
     With reference additionally to FIG. 4, it will be seen that when the brewer is initially energized, the red light  102   a  is lit continuously and the blue light  78  is in a flashing mode. The sensors  82 ,  84  provide the controller  86  with an indication of the liquid level in the tank  14 , and the controller performs a test  104  to determine if an adequate liquid supply is available. A “No” determination recycles the sequence, and a “Yes” determination illuminates the blue light  78  continuously. The controller  86  then performs a second test  106  using the signal from the temperature sensor  96  to determine if the liquid in the metering chamber  16  has been heated to the desired brew temperature. A “No” determination recycles the sequence, and a “Yes” determination extinguishes the red light  102   a  and illuminates the green light  102   b , indicating that the brewer is ready to perform a brew cycle. 
     The user then opens the drawer  88  and inserts a filter cartridge  46 . The switch  94  provides the controller with a signal indicating that the drawer is open, in response to which the controller extinguishes the green light  102   b . The controller then performs a test  108  to determine if the drawer had been closed. A “No” determination recycles the sequence, and a “Yes” determination causes the controller to intermittently illuminate the green light  102   b , and to commence the brew cycle by energizing pump  48  and deenergizing the heater  68 . 
     The air pump  48  then pneumatically effects the following sequence of system operation. The bladder  42  is inflated, the pushing shaft  28  and the baffle  70  downwardly, until the gasket  33  is pressed against the seat  20  to seal off the liquid in the metering chamber  16  from the remainder of the tank  14 . The downward movement of the shaft  28  also produces downward pivotal movement of the arm  34  against the resistance of the spring  40 , which in turn results in the lid and bottom of the cartridge  46  in the brewing chamber  44  being pierced respectively by probes  58 ,  60 . 
     Compressed air is then fed into the metering chamber  16  via the hose  50 , causing a metered mount of liquid to be expelled and fed to the cartridge  46  via the hose  56  and the tubular probe  58 . The resulting brewed beverage exits the cartridge probe  60  and is received in the underlying cup  64 . 
     At the conclusion of the brew cycle, compressed air purges the metering chamber  16 , and the resulting pressure drop is sensed by the pressure sensor  98 . The controller then responds by deactivating the pump  46  and the system is vented. The bladder  42  then collapses, allowing an upward displacement of the shaft  28  under the return force of the spring  40 . The baffle  70  is thus raised above the seat  20 , allowing air in the chamber  16  to be displaced by liquid in the tank  14 . The return force of the spring  40  also pivots arm  34  upwardly, which in turn removes the probe  58  from the cartridge  46 . 
     The drawer  88  may then be opened and the spent cartridge  46  removed from the brewing chamber, readying the system for the next cycle. The heater  68  is reenergized to heat the liquid that has refilled the metering chamber  16 . 
     Various modifications may be made to the embodiment herein disclosed. For example, the shaft  28  may be vertically reciprocated by other means such as for example a motor-driven gear drive, or manual operation of the arm  34 . The metering chamber  16  and the seat  20  may be formed on a separate cup-shaped insert received in the tank, rather than being formed integrally with the tank. The operation of pump  48  may be controlled by a timed sequence rather than in response to pressure in the metering chamber. Different visual indicators may be employed, and audible warning devices may be included to indicate various conditions, e.g., if the tank is either empty or in danger of being overfilled. An immersion heater may be employed in place of the external heating element  68 . 
     FIG. 5 is a vertical sectional view taken through an alternative embodiment single serve beverage brewer  200 . This brewer  200  is substantially similar to the brewer  10  illustrated in FIG. 1, with the principal exception that the brewer  200  includes several pneumatic pumps to control the brewing process. Specifically, the brewer  200  includes an air pump  202  that inflates the air bladder  42 . A first pneumatic brew pump  204  provides compressed air into conduit  206 , which routes the compressed air through a check valve  208 , and into the pneumatic port  52 . A pressure sensor  212  is connected to the conduit  206 . The pressure sensor  212  is preferably a dual threshold pressure sensor that provides a first signal on a line  214  indicative of when the pressure is above or below and first pressure threshold value (e.g., 1.5 psi), and a second signal on a line  215  indicative of when the pressure is above or below a second pressure threshold value (e.g., 7 psi). Such pressure sensors are available for example from World Magnetics (www.worldmagnetics.com) and from Micropneumatics Logic. The brewer  200  also includes an interrupt brew pump  214  that provides compressed air into conduit  216 , which routes the compressed air through a check valve  218 , and into conduit  220 . The conduit  220  routes the compressed air from the interrupt brew pump to a flow line  222 , which routes compressed air through a check valve  224  to the tubular probe  58 . 
     FIG. 6 is a block diagram illustration of the control system associated with the brewer illustrated in FIG. 5. A controller  230  (e.g., a microcontroller) receives Boolean signals from the pressure sensor  212 , the drawer switch  94  and the optical sensors  82 ,  84 . The controller also receives temperature threshold signals from a comparator circuit  241 . The comparator circuit  241  receives a temperature signal on a line  239  from the temperature sensor  96 . The circuit  241  includes a first comparator (not shown) that provides a Boolean signal on the line  240  indicative of whether or not the temperature is above or below a first temperature threshold value (e.g., 186° F.). The circuit  241  also includes a second comparator (not shown) that provides a Boolean signal on a line  244  indicative of whether or not the temperature is above or below a second temperature threshold value (e.g., 193° F.). The first and second temperature threshold values are used as set points for a heater control routine to be discussed hereinafter. The controller  230  also receives an input signal on a line  234  from a brew button  232  located on the brewer control panel. We shall now discuss the operation of the pumps  202 ,  204 ,  214  and a purge value  361 . 
     FIGS. 7A and 7B (collectively FIG. 7) together are a flow chart illustration of a brew cycle routine  700  performed by the controller  230 . The controller  230  is preferably a microcontroller such as a model PIC16C57 manufactured by Microchip (www.microchip.com). This microcontroller includes on chip program memory, RAM and a CPU. In this embodiment, the steps illustrated in FIG. 7 represent executable program instructions that are stored in the microcontroller program memory and periodically executed by the CPU. 
     The routine  700  includes a test  702  that determines if the brewing process should begin. This test checks the state of the brew signal on the line  234  (FIG. 6) that is generated by a brew button located on the brewer, and depressed when the user wishes to brew a beverage. If the signal on line  234  indicates that a user has not depressed the brew button, then the remaining steps of the routine  700  are not executed. However, if the brew signal indicates that the user has depressed the brew button, test  703  checks the liquid level sensors  82 ,  84  (FIG. 6) to ensure that there is water in the brewer. If there is not, step  705  is performed to flash the water column light  78  (FIG. 6) to call attention to the tubular transparent column that indicates the water level. If there is enough water in the brewer, test  706  is performed to determine if the water temperature is hot enough for brewing. The test  706  checks the status of the Boolean signal on line  240  (FIG. 6) to determine if the water temperature is above the first threshold value. If the temperature is not above the first threshold value (e.g., the signal on the line  240  is a logical zero) then step  708  is executed to illuminate a status light (e.g., a yellow light) to indicate the water temperature is not hot enough for brewing. If the water temperature is hot enough for brewing, a test  710  is performed to check that the cartridge drawer  88  (FIG. 5) has been closed in the last thirty (30) seconds. This test helps to ensure that the user has placed an unused cartridge into the brewer. Specifically, the test  710  checks the status of the signal from the drawer switch sensor  94  (FIGS.  5  and  6 ). If the drawer  88  has not been closed in the last thirty seconds, step  712  is performed to illuminate a status light. If the drawer is closed, then the system is ready for brewing and step  714  is performed to turn the heater off, close the purge valve  361  (FIG. 6) and turn the bladder pump  202  (FIG. 6) on. 
     Referring to FIG. 5, turning the bladder pump  202  on causes the air bladder  42  to inflate, which moves the shaft  28  downward sealing the gasket  33  against the seat  20  to establish the metering chamber area  16 . This also causes the arm  34  to pivot, causing the probe  58  to puncture the cartridge  46  to establish a flow path inlet to the cartridge. The downward force from the arm  34  also forces the cartridge against and to be pierced by the flow outlet needle  60 , thus establishing a flow exit path from the cartridge. Referring to FIGS. 5 and 7, following the step  714  where the bladder pump is turned on, step  716  is performed to delay for several seconds (e.g., five seconds), before commanding the brew pump  204  (FIG. 5) on in step  718 . The delay accounts for the time is takes for the shaft  28  to drive the gasket  33  into position to seal the metering chamber, and for the arm  34  to move into the brewing position. 
     While the brew pump  204  is on and the bladder  42  is inflated to seal the gasket  33  against the seat  20 , compressed air enters the metering chamber  16  through port  223  driving water in the metering chamber into the metering tube  54 . The water then passes through the brew valve check valve  224  into the cartridge  46 . The water enters the cartridge through the downwardly projecting apertured probe  58 , passes through beverage extract and a filter within the cartridge, and exits the cartridge through the hollow piercing member  60  to a cup below. 
     Referring again to FIGS. 5 and 7, once the brew pump  204  is turned on in the step  718 , the controller performs a safety test  722 . The test  722  monitors the sensed pressure signal value on the line  215  (FIG.  6 ), which is indicative of whether or not pressure in the metering chamber exceeds a maximum pressure threshold value (e.g., 7 psi). If the pressure the pressure exceeds the maximum pressure threshold value, then step  724  commands the pumps off. Step  724  also commands a purge valve  361  (FIG. 5) to the open, in order to deflate the air bladder  42  causing the shaft  28  to move vertically upward and the probe  58  to disengage from the cartridge  46 . The test  722  also checks if the brew pump  204  has been on for an excessive amount of time and executes the step  724  if it has. Following step  724 , step  725  is performed to determine if an over pressure has been detected for two consecutive brewing cycles. That is, test  725  determines if during the brewing of the last two cups, was an over pressure detected during each brew. If it was detected during two consecutive brews, then the flow path between the metering tube  54  and the probe  60  may be at least partially blocked. Therefore, step  727  is performed to illuminate a status light(s) indicative of a detected condition where the user should clean the flow path between and including the metering tube  54  and the probe  60 . 
     If the test  724  determines an over pressure or a time-out situation does not exist, an interrupt brew routine illustrated in FIG. 8 is performed. 
     FIG. 8 is a flow chart illustration of a interrupt brew logic routine  800 . This routine controls the operation of the interrupt brew pump  214  (FIG.  5 ), which provides a user the ability of customize the amount of water in their brewed beverage, and hence the taste. The routine includes a test  802  to check if the brew pump  204  (FIG. 5) is on. If the brew pump  204  is not on, then the routine exits. However, if the brew pump  204  is on, then a test  804  is performed to determine if the user has depressed the brew button  232  (FIG.  5 ). If the brew button is not depressed, the routine exits. If the user has depressed the brew button, then in step  806  the brew interrupt pump  214  (FIG. 5) is turned on, and the brew pump  204  (FIG. 5) is turned off. As a result, compressed air flows through the flow line  220  (FIG.  5 ), into the flow line  222  (FIG. 5) and through the tubular probe  58  (FIG. 5) into the cartridge. The brew interrupt pump remains on for about six seconds, to drive the water in the flow line  222  through the tubular probe  58  to the cartridge. Significantly, once the brew interrupt pump  214  is turned on, water no longer flows from the metering chamber  14  (FIG. 5) to the metering probe  54  (FIG.  5 ). Execution then returns to test  726  illustrated in FIG.  7 . 
     Test  726  is performed to determine if the air pressure in the metering chamber  16  (FIG. 5) has dropped below a threshold value indicating that a desired amount of liquid has been output from the brewer. The threshold value is preferably a fraction of the nominal maximum sensed pressure during the brewing cycle. For example, the threshold may be 75% of the maximum sensed pressure during the brewing cycle. Alternatively, the threshold may be a constant value. If the user has not depressed the brew button while the brew pump is on in order to terminate the brew cycle, then the pressure will nominally drop below the threshold value when a predetermined amount of liquid has been delivered from the metering chamber. The predetermined amount (e.g., eight fluid ounces) is set based upon the size of the metering chamber. However, the user can control the amount of liquid in the brewed beverage by depressing the brew button while the brew pump is on. This causes the brew pump to turn off, and the brew interrupt pump to turn on in order to blow out the water in the line flow line  222 . Significantly, depressing the brew button  232  (FIG. 5) while the brew pump is on, terminates the brew cycle causing an amount of liquid less than the predetermined amount to be delivered during the brew cycle. 
     The test  726  monitors the sensed pressure value on the line  214  from the pressure sensor  212  (FIG.  5 ). If the pressure has not dropped (i.e., the signal on the line  214  indicates the pressure is above the threshold), execution returns to test  322 . 
     Once the test  726  determines that the pressure has dropped (caused by either delivering the predetermined amount of liquid or a brew interrupt), step  728  is performed to delay several seconds in order to blow residual liquid from the liquid flow path leading to the probe  58  (FIG.  5 ). During this delay the brew pump  204  or the interrupt brew pump  214  (FIG. 5) remains on, depending of course which one is on prior to the delay  228 . Significantly, blowing out the flow path leading to the cartridge ensures that only hot water is used to brew, which is especially important if there is a substantial period between uses. In addition, blowing out the flow path removes liquid from the used cartridge for cleaner disposal. One of ordinary skill will recognize that during the delays the controller performs other tasks such as input signal processing, output signal processing, storage tank temperature control, and background and foreground built-in-tests, and/or other control and monitoring routines. The delays may be implemented by hardware or software counters. 
     Once the delay time of step  728  has elapsed, step  730  is executed to command the pumps  202 ,  204 ,  214  off. Step  732  is then performed to open the purge valve  361  (FIG. 5) to deflate the air bladder  42 . Deflating the air bladder  42  causes the shaft  28  to move vertically upward, which allows water to enter (i.e., refill) the metering chamber  16  (FIG. 5) from the tank  14  (FIG.  5 ). 
     Referring again to FIG. 5, to brew another beverage, the drawer  44  is opened, the used cartridge is removed, a new cartridge is inserted and the drawer  44  is returned to the closed position, and the start brew button is depressed again. 
     FIG. 9 is a flow chart of a built-in-test routine  900  periodically performed by the controller. The routine  900  includes a test  902  to determine if the heater has been on for an excessive amount of time (e.g., twelve minutes), or it has been off for too long. If either of these conditions is true, step  904  commands the heater off. Step  904  may also command the pumps off, and the purge valve open. Step  906  then annunciates the fault/alarm condition and the system is placed into an “off/safety state” to prevent further brewing. Otherwise, test  908  is performed to determine if the metering chamber  14  (FIG. 5) is over pressurized. The test  908  reads the status of the signal on the line  215  (FIG. 5) from the pressure sensor (FIG.  5 ), and if the status of the signal indicates the pressure exceeds the second pressure threshold value associated with an over pressure, step  910  is performed to turn the pumps off and open the purge value. Step  912  is then performed to annunciate the fault/alarm condition and the system is placed into the “off/safety state” to prevent further brewing. 
     FIG. 10 is a flow chart illustration of a routine  1000  for controlling the liquid heater. The routine  1000  includes test  1002  that checks if the brew pump  204  (FIG. 5) is on. If it is, then the heater has already been commanded off (step  714  in FIG.  7 ), and heater remains off while the brew pump is on. However, if the brew pump is not on, then test  1003  checks to see if the water level in the brew is above the minimum threshold. This test is performed by checking the status of the signal from optical sensor # 1   82  (FIGS.  2 A and  5 ). If there is not enough water in the brewer the heater is turned off in step  1006 . Otherwise, test  1004  is performed to determine if the water temperature is above a maximum water temperature threshold value. This test checks the status of the signal on the line  244  (FIG.  5 ). If the Boolean signal on the line  244  (FIG. 5) indicates that the temperature is greater than this threshold value, then the water is hot enough and the heater is commanded off in step  1006 . Test  1008  is then performed to determine if the water temperature is below a minimum water temperature value. This test checks the status of the Boolean signal on the line  240  (FIG.  5 ). If the signal on the line  240  (FIG. 5) indicates that the temperature is less than the minimum water threshold value, then the heater is commanded on in step  1010 . If the test  1008  determines the water temperature is not below the minimum water threshold value, then the temperature is between the minimum and maximum threshold temperature values (i.e., the threshold values set in the comparator circuit  241  of FIG.  5 ). Therefore, step  1012  is performed to turn the heater on and off with a 50% duty cycle. 
     FIG. 11 is a flow chart illustration of a routine  1100  for checking the liquid level within the storage tank  14  (FIG.  5 ). The routine  1100  includes test  1102  to check if the water level in the tank  14  (FIG. 5) is too high. The test checks the status of the optical sensor # 1  (FIGS. 2A and  5 ). If the optical sensor # 1   82  indicates the tank is full, then step  1104  is performed to provide an audio indication to the user to stop filling the unit via inlet  17  (FIG.  5 ). For example, several beeps may be output from speaker  266  (FIG.  5 ). If the tank is not full, then test  1106  is performed to determine if the water level is too low. If it is, then step  1108  is performed the flash the water column light  78  (FIGS.  2 A and  5 ). 
     While the present invention has been described in the context of a preferred embodiment that senses air pressure to determine when the desired amount of liquid has been delivered from the metering chamber, the present invention is not so limited. For example, a level sensor (e.g., a float switch) may be located in the metering chamber to determine when the liquid in the chamber is below a certain level. In addition, the brew pump may be simply commanded on for a set period of time sufficient to ensure that the predetermined amount of liquid has been delivered from the metering chamber. Notably, it suffices that in all these embodiments of the present invention compressed air is used to drive liquid from the metering chamber. In addition, although the brewer is discussed in the context of manually adding water to the system, one of ordinary skill will recognize that the system may include automatic refill if connected for such operation to the plumbing. 
     Although the present invention has been discussed in the context of an automated brewing system that includes a microcontroller, one of ordinary skill will recognize that there a number of different techniques for controlling the delivery of the compressed air to the metering chamber. For example, a state machine may be used rather than a CPU. In addition, the controller may be an analog system rather than a digital controller. Furthermore, a pneumatic controller rather than an electronic controller may be used to control delivery and venting of the compressed air. While obvious, it should also be noted the present invention is certainly not limited to the delay values, threshold values or brewing sizes discussed herein. In addition, it is contemplated that rather than an electrically controllable valve, the purge valve may be mechanically linked to the arm so the valve opens as the arm moves from the beverage brewing position. In addition, the controller may also include an analog-to-digital converter (ADC), which allows analog temperature and pressure signal values to be input to the controller and digitized for use in the control and monitoring routines. 
     The present invention may also operate in a “vending” environment. That is, as a vending machining, the system would not start brewing until money has been deposited or an account debited. For example, test may check to ensure the required fee has been paid before brewing is allowed to start. 
     Although the present invention has been shown and described with respect to several preferred embodiments thereof, various changes, omissions and additions to the form and detail thereof, may be made therein, without departing from the spirit and scope of the invention.