Abstract:
The present invention relates to a portable, personal breath tester device for testing the blood alcohol content of the user of the device. The breath tester comprises a circuit board, wherein a sensor, a liquid crystal display, and a processing unit are installed on and electrically connected to the circuit board. The processing unit receives a voltage signal from the sensor representing the blood alcohol content of the user and converts the voltage signal to a precise value that is displayed on the liquid crystal display.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. provisional patent application No. 60/746,716, filed on May 8, 2006. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates the gaseous breath detection devices, and methods for using the same, and more particularly to a portable personal gaseous breath detection device incorporating digital circuitry to analyze a sample of alveolar air from the user of the device for the presence of alcohol. 
   2. Background Art 
   The present invention relates generally to devices and methods for determining the concentration of alcohol in a mixture of gases and more particularly, the invention relates to a device and method for determining the concentration of alcohol in a breath sample for application in sobriety detection systems. 
   Various techniques have been employed for calculating a person&#39;s blood alcohol concentration by measuring breath samples. A first method employs an infrared absorption technique for determining the blood alcohol concentration. Breath alcohol levels are measured by passing a narrow band of IR light, selected for its absorption by alcohol, through one side of a breath sample chamber and detecting emergent light on the other side. The alcohol concentration is then determined by using the well-known Lambert-Beers law, which defines the relationship between concentration and IR absorption. This IR technology has the advantage of making real-time measurements; however, it is particularly difficult and expensive to achieve specificity and accuracy at low breath alcohol concentration levels. Also, the IR detector output is nonlinear with respect to alcohol concentration and must be corrected by measurement circuits. 
   A second method employs a fuel cell together with an electronic circuit. In breath alcohol testing devices presently used commercially, in which fuel cells are employed, the conventional way of determining breath alcohol is to measure a peak voltage across a resistor due to the flow of electrons obtained from the oxidation of breath alcohol on the surface of the fuel cell. Although this method has proven to have high accuracy levels, there are a number of problems. The peaks become lower with repeated use of the fuel cell and vary with different temperatures. In order to produce a high peak, it is customary to put across the output terminals of the fuel cell a high external resistance, on the order of a thousand ohms, but the use of such a high resistance produces a voltage curve which goes to the peak and remains on a high plateau for an unacceptably long time. To overcome that problem, fuel cell systems began to short the terminals, which drops the voltage to zero while the short is across the terminals. However, it is still necessary to let the cell recover, because if the short is removed in less than one-half to two minutes after the initial peak time, for example, the voltage creeps up. Peak values for the same concentration of alcohol decline with repeated use whether the terminals are shorted or not, and require 15-25 hours to recover to their original values. 
   In addition, individual fuel cells differ in their characteristics. All of them slump with repeated use in quick succession and also after a few hours&#39; time of non-use. They degrade over time, and in the systems used heretofore, must be re-calibrated frequently. Eventually, they degrade to the place at which they must be replaced. Presently, the cell is replaced when it peaks too slowly or when the output at the peak declines beyond practical re-calibration, or when the background voltage begins creeping excessively after the short is removed from the cell terminals. 
   Systems employing this method were also cost prohibitive for many applications. One reason for the high cost associated with the fuel cell techniques is that the method requires that the breath sample be of a determinable volume. Historically, this has been accomplished through the use of positive displacement components such as piston-cylinder or diaphragm mechanisms. The incorporation of such components within an electronic device necessarily increases the costs associated with the device. 
   In a third method, the alcohol content in a breath sample is measured using a semiconductor sensor commonly referred to as a Tagucci cell. Among the advantages of devices utilizing semiconductor sensors are simplicity of use, light weight, and ease of portability and storage. Such units have been employed in law enforcement work as “screening units,” to provide preliminary indications of a blood alcohol content and for personal use. Although this method provides a low cost device, instruments incorporating this method have proved to have poor accuracy because of the need to hold input voltage signals to the electronic components of the device at constant, steady, regulated levels. 
   Accordingly, it is desirable to have a breath test device that is easy to use yet accurate in its results, is portable and is an item that the user will remember to bring with him/her to an event or location where alcohol is being consumed. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention provides a electronic breath analyzer. The electronic breath analyzer includes a gas sensor for alcohol detection. The gas sensor having a heater and a gas sensing element. A micro controller including a general control output, a reference value input and a gas sensing element input. The gas sensing element input is coupled to the gas sensing element. The micro controller is adapted to provide an initiate reading and comparison signal at the general control output. A reference value register includes a reference value in the register, and having a read initiate input and a reference value output. A general control module includes a control input, a read register output, and an enable gas sensor output. The control input is coupled to the general control output, the read register output is coupled to the read initiate input and provides a read initiate signal upon receiving the initiate reading and comparison signal at the general control module. The enable gas sensor output is coupled to the gas sensor and produces an enable signal upon receiving the initiate reading and comparison signal at the general control module. 
   In one embodiment, the general control module includes an NPN transistor having an emitter coupled to VCC, the base coupled to the micro controller, and the collector is coupled to the sensing element through a resistor, and the collector is also coupled to VCC of a memory chip to enable shifting serial reference data to the micro controller. Concurrently, the micro controller produces a clock signal at the clock input of the memory chip. 
   In one embodiment, a first and second stage transistor circuit is provided to amplify current coupled to the gas sensor. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  shows a block diagram of a breath tester system according to a preferred embodiment of the present invention; 
       FIGS. 2   a - c  show a circuit schematic diagram of a breath tester system according to a preferred embodiment of the present invention; 
       FIG. 3  shows detailed schematic of the pin configuration of the microprocessor of a preferred embodiment of the present invention; 
       FIG. 4  is a table providing details of the pins of the microprocessor of  FIG. 3 ; 
       FIGS. 5   a - c  show graphical representations of output waveforms of voltage (vertical axis) over time (horizontal axis) of electrical components of a preferred embodiment of the present invention; 
       FIG. 6  shows a flow diagram of a breath tester system according to a preferred embodiment of the present invention in operation; 
       FIG. 7  shows a flow diagram of the steps of calibrating the breath tester of the present invention; 
       FIGS. 8   a - b  show a circuit schematic diagram of a breath tester system according to a second preferred embodiment of the present invention; 
       FIG. 9  shows a detailed schematic of the pin configuration of the microprocessor of a preferred embodiment of the present invention; 
       FIGS. 10   a - 10   b  are tables providing details of the pins of the microprocessor of  FIG. 9 ; and 
       FIG. 11  is a block diagram of the microprocessor of a preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2  show a breath tester device  10  in accordance with a first preferred embodiment of the present invention for testing a breath sample from the user of the device and calculating the blood alcohol content of the breath sample. As is seen in the block diagram of  FIG. 1  and the circuit schematic of  FIG. 2 , the breath tester  10  comprises the following modules: Processor Module  12 ; Crystal Module  14 ; Switch Module  16 ; Power Module  18 ; Sensor Preheat Module  20 ; Sensor Module  22 ; General Control Module  24 ; Look-Up Reference Module  26 ; Display Module  28 ; and Reset Module  30 . The individual modules have been organized and named for purposes of convenience in describing the structure and arrangement of components in this preferred embodiment and should not be considered as limiting in any manner. 
   As is seen in  FIG. 1 , the Processor Module  12  is central to and electrically coupled to the remaining modules. In addition, the Power Module  18  is also coupled to the Sensor Preheat Module  20 . The Sensor Preheat Module  20  is in turn coupled to the Sensor Module  22 . The Sensor Module  22  is coupled to the General Control Module  24 , which is coupled to the Look-Up Reference Module  26 . 
   The circuit elements of the modules shown in  FIG. 1  will now be described in greater detail. The Processor Module  12  is composed of a microprocessor chip  32  and programming unit  34 . In a preferred embodiment of the present invention, the microprocessor  32  comprises an 8-bit RISC type chip with low power, high speed CMOS technology and having 16K×13 bits of internal memory. The microprocessor  32  further comprises an on-chip watchdog timer, program ROM, data RAM, LCD driver, programmable real time clock/counter, internal interrupt, power down mode, built-in three-wire SPI, dual PWM (Pulse Width Modulation), 6-channel 10 bit A/D converter, and tri-state I/O.  FIG. 3  shows the pin configuration of microprocessor  32  in detail and  FIG. 4  shows a table providing additional description of each pin on the microprocessor  32 . The microprocessor  32  used in a preferred embodiment of the present invention is manufactured by Elan Microelectronics Corp. and is sold as Product No. eFH5830AD. However, any suitable microprocessor can be utilized for purposes of the present invention. 
   Referring to the operation of the Switch Module  16  and Power Module  18  (as shown in  FIG. 2   c ), depressing the switch  36  will ground the positive terminal of the power source  38  causing a voltage to flow along the established pathway. The emitter end of the transistor  40  is coupled directly to the positive terminal of power source  38  and therefore receives voltage Vb from the power source  38 . The base of the transistor  40  is also coupled to the positive terminal of power source  38  across resistor  42 . Accordingly the base end of transistor  40  receives a voltage of Vb minus the voltage drop across resistor  42 . Because transistor  40  is in a P-N-P configuration and the voltage at the base is less than the voltage at the emitter, the transistor is biased closed, coupling the emitter and collector of transistor  40  and enabling Vb minus the voltage drop across transistor  40  to flow towards the step-up converter  44 . 
   The step-up converter  44 , steps up the input voltage signal to a voltage of +5V. In another preferred embodiment of the present invention, shown in  FIG. 8   b  and described in detail below, the step-up converter  44  steps up the input voltage signal to a voltage of +4V. The +5V voltage signal generated by the Power Module  18  is coupled to the components of the Processor Module  12  via the AVDD power pin (Port  7 ), the General Control Module  24 , the Look-Up Reference Module  26 , and the Reset Module  30 . Voltage Vb from the power source  38  is coupled to the Sensor Preheat Module  20 . In a preferred embodiment of the present invention the step-up converter  44  is a PFM controlled, step-up DCIDC converter manufactured by Torex Semiconductor and is sold under Product Number XC6382. The power source in this embodiment of the present invention is a 3V DC battery. 
   The Switch Module  16  (shown in  FIG. 2   c ) also comprises an “electronic” switch that, when triggered, will enable the power source  38  to provide voltage to the device  10  if the user of the device releases the switch  36 . The base of transistor  76  is coupled to the PC3 input/output pin (Port  33 ) of microprocessor  32 . Once powered up, the microprocessor  32  generates and sends an output voltage signal to the base of the transistor  76 . Because transistor  76  is configured in the N-P-N configuration and the emitter is coupled to ground, the output voltage signal causes the transistor  76  to be biased closed, coupling the emitter and collector. Because the collector of transistor  76  is coupled to the base of the transistor  40 , transistor  76  serves as an electronic switch, keeping transistor  40  biased closed to enable Vb from the positive terminal of power source  38  to supply a voltage to the Sensor Preheat Module  20  and the step-up converter  44 . When the switch  36  is released and the microprocessor  32  terminates the power signal sent to the base of the base of transistor  76 , then the power source  38  will no longer provide voltage to the components of the device  10 . The microprocessor  32  includes an automatic shut-off routine that terminates the power signal sent to the base of the transistor  76  after a preset term of inactivity. 
   Turning to the Reset Module  30  (shown in  FIG. 2   c ), the emitter of transistor  46  is coupled directly to the +5V voltage signal from the step-up converter  44  of the Power Module  18 . The voltage at the base of the transistor  46  comprises the +5V voltage signal from the step-up converter  44  minus the voltage drop across resistor  48 . Because transistor  46  is in a P-N-P configuration, the transistor  46  is biased closed, coupling the emitter and collector and sending an input signal to the RESET pin (Port  21 ) of microprocessor  32  causing the breath tester circuit to reset itself and prepare to take a new reading. 
   Turning to the Sensor Preheat Module  20  (shown in  FIG. 2   b ), at one end of the module  20 , the emitter of transistor  50  is coupled directly to the positive terminal of power source  38  and, therefore, has a voltage of Vb. The second end of the Sensor Preheat Module  20  is coupled to the PCIIPWMI pin (Port  31 ) of the microprocessor  32  and receives a power signal from the microprocessor  32 . The breath tester circuit utilizes the pulse width modulation function of the microprocessor  32  to control transistors  50  and  52  of the Sensor Preheat Module  20  and provide to the Sensor Module  22  constant voltage with a high current. The transistor  52  is configured in the N-P-N configuration with the emitter coupled to ground. Accordingly, providing a positive voltage signal to the base of transistor  52  will bias the transistor  52  closed, coupling the base of transistor  52  to ground. The base of transistor  50  is also coupled to the collector of transistor  52  and is therefore responsive to the voltage signal at the collector of transistor  52 . As is seen in the waveform diagrams of  FIGS. 5   a - 5   c , when the microprocessor  32  provides a pulse voltage signal to the Sensor Preheat Module  20  through the PCIIPWMI pin, the transistor  52  is biased closed and the voltage at the collector is coupled to ground. Because the transistor  50  is in a P-N-P configuration, when the voltage at the base of transistor  50  is coupled to ground via transistor  52 , the transistor  50  is biased closed, coupling the emitter and collector and providing a steady voltage to the Sensor Module  22 . The Pulse Width Modulation signal sent by the microprocessor  32  controls the operation of transistors  50  and  52  to provide a 0.9V equivalent DC voltage to the Sensor Module  22 . 
   In a preferred embodiment of the present invention, the Sensor Module  22  comprises a tin dioxide semiconductor gas sensor  54 . Tin dioxide sensors have high sensitivity to the presence of alcohol, however, it is contemplated that other suitable gas sensors are available and can be utilized in the present invention. The sensor  54  comprises a heating element  56  and a sensor element  58 . The heating element  56  comprises a resistor having a first end coupled to the voltage output of the Sensor Preheat Module  20  and a second end coupled to ground. The sensing element  58  comprises a variable resistor having a conductivity that varies depending on the temperature of the sensor and the concentration of alcohol vapors present. A tin dioxide gas sensor manufactured by FiS, Inc. of Japan and is sold under Product Number SB-30 is utilized in this preferred embodiment of the present invention. 
   In order to obtain optimum performance from the sensor  54  the voltage applied across the heating element  56  must be held steady. The sensor  54  of the present invention exhibits optimum performance when a voltage of 0.9V is applied to the heating element  56 . As previously described, the components of the Sensor Preheat Module  20  are selected to provide a constant 0.9V to the heating element during operation of the breath test device  10  of the present invention. Reference point  60  is coupled to microprocessor  32  at AD2/P61 input pin (Port  16 ) to enable the microprocessor  32  to monitor the voltage at reference point  60 . 
   The sensing element  58  operates at a circuit voltage of preferably less than 5V. The sensor  54  output is also controlled by the transistor  62  of the General Control Module  24 . The emitter of transistor  62  is coupled to the output of the step-up converter  44  of the Power Module  18  and is at a voltage of 5V. Whereas transistor  62  is configured in a P-N-P configuration, the emitter will be coupled to the collector when the 5V power signal is applied to the emitter. By controlling the voltage to the output terminal of the sensor  54 , transistor  62  is controlling the output power signal of sensor  54 . The output signal representing the voltage at the sensing element  58  is measured at reference point  66  adjacent to load resistor  68  and is coupled to the microprocessor  32  at the ADI/P60 input pin (Port  17 ) for monitoring by the microprocessor  32 . 
   The transistor  62  also controls the voltage (Vcc) to the memory  70  of the Look-Up Reference Module  26 . In a preferred embodiment, the memory  70  comprises an electrically erasable and programmable read-only memory (EEPROM) unit having at least 2048 bits of serial memory. An EEPROM suitable for use in the present invention is manufactured by Atmel Corp. and sold under Product No. AT2402C. The EEPROM  70  is used to store calibration data and look-up tables utilized by the microprocessor  32  during operation of the breath test device  10 . EEPROM  70  comprises a plurality of memory locations which serve as individually addressable reference registers containing values for the microprocessor to compare against the output of the sensing element during calibration and operation of the electronic breath analyzer. The EEPROM is coupled to the base of transistor  62  and operates at a voltage (Vcc) provided by and controlled by transistor  62 . 
   The EEPROM  70  is used to store calibration and look-up table information used by the microprocessor  32  to calculate the blood alcohol content from the output voltage signal of the sensing element  58 . The breath tester device  10  is calibrated prior to use and may be recalibrated with new calibration and look-up table information being entered at the programming unit  34  and stored on the EEPROM  70 . Data stored on the EEPROM  70  is clocked out to the microprocessor  32  at Serial Data (SDA) pin in response to receiving clocking input signals from the microprocessor  32  at the Serial Clock (SCL) pin. The SDA pin of the EEPROM  70  is coupled to the P76/SCK pin (Port  23 ) of the microprocessor  32 . The SCL pin of the EEPROM  70  is coupled to the P74/SDI input pin (Port  25 ) and P75/SDO output pin (Port  24 ) of the microprocessor  32 . 
   The speed of the microprocessor  32 , and in turn the clocking signal generated by the microprocessor  32  and received by the EEPROM  70 , is determined by the oscillation of the crystal  72  of the Crystal Module  14 . It is contemplated that any suitable crystal can be used in the present invention. While in this embodiment of the present invention, the memory  70  is a separate component than the microprocessor  32 , it is contemplated that a microprocessor with sufficient internal memory can be utilized to perform the same functions as the separate memory and microprocessor configuration described herein. 
   The microprocessor  32  is also coupled to a Display Module  28  (shown in  FIG. 2   a ). In a preferred embodiment of the present invention, the Display Module  28  comprises a liquid crystal display (LCD)  74 . After performing the comparison of the data collected at reference point  60  against the date stored in EEPROM  70 , the microprocessor  32  will cause the appropriate output to be displayed on the LCD  74 . The LCD  74  is also used to display messages to the user of the device  10 , as will be described in detail below. 
   Referring now to  FIG. 6 , along with  FIGS. 1 and 2 , a flow chart showing operation of the breath test device  10  of the present invention is shown. The first step of operation  76  of the device  10  is to depress the switch  36  causing the Preheat Sensor Module  20  to warm up the Sensor Module  22  to proper operating temperature ( 78 ,  FIG. 6 ). While the Sensor Module  22  is warming up  78 , the microprocessor  32  sends output signals to the LCD  74  causing the LCD  74  to display a WAIT message  80  to the user of the device  10 . When the Sensor Module  22  is at the proper operating temperature, the microprocessor  32  will send output signals to the LCD  74  causing the LCD  74  to display a BLOW message  82  to the user of the device  10 , indicating to the user that the unit is ready to be used. Next, the user of the device  10  will blow on the Sensor Module  22  for three seconds ( 84 ,  FIG. 6 ) to ensure that the sensing element  58  is exposed to a sufficient volume of alveolar air to take a proper reading. The Sensor Module  22  generates an output signal that is sent to the microprocessor  32  for comparison against stored values from the EEPROM  70  to determine the alcohol content of the sample of air ( 86 ,  FIG. 6 ). Once the comparison and calculation is performed by the microprocessor  32 , the microprocessor  32  generates and sends the appropriate output signals to the LCD  74 , causing the LCD  74  to display the calculated blood alcohol level in units between 0.02% and 0.0%, in increments of 0.01% ( 88 ,  FIG. 6 ). 
   If the user of the device  10  desires to have additional readings taken, the user will depress the switch  36  ( 76 ,  FIG. 6 ) causing the system to reset for a subsequent reading. If the user does not test subsequent samples, the microprocessor  32  will automatically shut the device  10  off after a preset period of time ( 90 ,  FIG. 6 ). 
     FIG. 7  shows a flow diagram of the calibration process of the present invention. Referring to  FIGS. 2 and 7 , calibration begins by jumper shorting  92  the input pin P 71  (Port  28 ) of the microprocessor  32  as a first point of calibration for 0.02% blood alcohol content. Next  94 , the switch  36  is depressed to provide power to the device  10 . The Sensor Module  22  is preheated  96  for one to fifteen seconds, dependant on the last time the device  10  was used. Once the Sensor Module  22  is preheated, a mixing solution is prepared with distilled water and ethanol to a represent a known blood alcohol content. In the present example, the mixing solution is prepared to represent a 0.02% blood alcohol content and is sprayed  98  on the Sensor Module. The microprocessor  32  is then calibrated with the 0.02% blood alcohol content data  100 . If the device is not to be calibrated for 0.08% blood alcohol content (decision  102 ), the calibration process is complete, and the process ends  114 . 
   Otherwise, when the device  10  is to be calibrated for 0.08% blood alcohol content as well, input pin P 72  (Port  27 ) of the microprocessor  32  is jumper shorted at a second point  104 . Next  106 , the switch  36  is depressed to provide power to the device  10 . The Sensor Module  22  is again preheated  108  for one to fifteen seconds, dependant on the last time the device  10  was used. However the preheat period should be relatively short because the device  10  was recently preheated for calibration of 0.02% blood alcohol content. Once the Sensor Module  22  is preheated, a mixing solution is prepared with distilled water and ethanol to a represent a 0.08% blood alcohol content and is sprayed  110  on the Sensor Module. The microprocessor  32  is then calibrated with the 0.08% blood alcohol content data  112  and the calibration process is complete  114 . 
   Referring to  FIGS. 8   a - b , a second preferred embodiment of the present invention is shown. The same reference numbers corresponding to similar circuit modules and circuit elements present in all preferred embodiments of the invention described herein will be utilized to describe the present preferred embodiment. As is seen in the circuit schematic of  FIGS. 8   a - b , the breath tester  10  comprises the following modules: Processor Module  12 ; Crystal Module  14 ; Switch Module  16 ; Power Module  18 ; Sensor Preheat Module  20 ; Sensor Module  22 ; Look-Up Reference Module  26 ; Display Module  28 ; and Reset Module  30 . The individual modules have been organized and named for purposes of convenience in describing the structure and arrangement of components in a preferred embodiment and should not be considered as limiting in any manner. 
   The Processor Module  12  is composed of a microprocessor chip  32 . In a preferred embodiment of the present invention, the microprocessor  32  comprises an 8-bit chip with low power, high speed CMOS technology and having LCD controller/driver and pulse width modulation features.  FIG. 9  shows the pin configuration of microprocessor  32  in detail and  FIGS. 10   a - 10   b  show tables providing additional description of each pin on the microprocessor  32 .  FIG. 11  provides additional details of the microprocessor  32 . The microprocessor  32  used in this preferred embodiment of the present invention is manufactured by Samsung Electronics Co., Ltd. and is sold as Product No. S3P9228. However, any suitable microprocessor can be utilized for purposes of the present invention. 
   Referring to the operation of the Switch Module  16  and Power Module  18  (shown in  FIG. 8   b ), depressing the switch  36  will ground the positive terminal of the power source  38  causing a voltage to flow along the established pathway. The emitter end of the transistor  40  is coupled directly to the positive terminal of power source  38  and therefore receives voltage Vb from the power source  38 . The base of the transistor  40  is coupled to the positive terminal of power source  38  across resistor  42 . Accordingly the base end of transistor  40  receives a voltage of Vb minus the voltage drop across resistor  42 . Because transistor  40  is in a P-N-P configuration and the voltage at the base is less than the voltage at the emitter, the transistor is biased closed, coupling the emitter and collector of transistor  40  and enabling Vb minus the voltage drop across transistor  40  to flow towards the step-up converter  44 . 
   The step-up converter  44 , steps up the input voltage signal to a voltage of +4V. The +4V voltage signal generated by the Power Module  18  is coupled to the components of the Processor Module  12  via the VDD power pin (Port  5 ), the Look-Up Reference Module  26 , and the Reset Module  30 . Voltage Vb from the power source  38  is coupled to the Sensor Preheat Module  20 . In a preferred embodiment of the present invention the step-up converter  44  is a PFM controlled, step-up DCIDC converter manufactured by Torex Semiconductor and is sold under product number XC6382. The power source  3  is in this embodiment of the present invention two 1.5V DC batteries. 
   The Switch Module  16  also comprises an “electronic” switch that, when triggered, will enable the power source  38  to provide voltage to the device  10  if the user of the device releases the switch  36 . The base of transistor  76  is coupled to the PO.2 input/output pin (Port  41 ) of microprocessor  32 . Once powered up, the microprocessor  32  generates and sends an output voltage signal to the base of the transistor  76 . Because transistor  76  is configured in the N-P-N configuration and the emitter is coupled to ground, the output voltage signal causes the transistor  76  to be biased closed, coupling the emitter and collector. Because the collector of transistor  76  is coupled to the base of the transistor  40 , transistor  76  serves as an electronic switch, keeping transistor  40  biased closed to enable Vb from the positive terminal of power source  38  to supply a voltage to the Sensor Preheat Module  20  and the step-up converter  44 . When the switch  36  is released and the microprocessor  32  terminates the power signal sent to the base of the base of transistor  76 , then the power source  38  will not provide voltage to the components of the breath test device  10 . The microprocessor  32  includes an automatic shut-off routine that terminates the power signal sent to the base of the transistor  76  after a preset period of inactivity. 
   Turning to the Reset Module  30  (shown in  FIG. 8   a ), the emitter of transistor  46  is coupled directly to the +4V voltage signal from the step-up converter  44  of the Power Module  18 . The voltage at the base of the transistor  46  comprises the +4V voltage signal from the step-up converter  44  minus the voltage drop across resistor  48 . Because transistor  46  is in a P-N-P configuration, the transistor  46  is biased closed, coupling the emitter and collector and sending an input signal to the RESET pin (Port  12 ) of microprocessor  32  causing the breath tester circuit to reset itself and prepare to take a new reading. Turning to the Sensor Preheat Module  20  (shown in  FIG. 8   b ), at one end of the module  20 , the emitter of transistor  50  is coupled directly to the positive terminal of power source  38  and, therefore, has a voltage of Vb. The second end of the Sensor Preheat Module  20  is coupled to the PO.1 input/output pin (Port  1 ) of the microprocessor  32  and receives a pulsed power signal from the microprocessor  32 . The breath tester circuit utilizes the pulse width modulation capability of the microprocessor  32  to control transistors  50  and  52  of the Sensor Preheat Module  20  and provide to the Sensor Module constant voltage with a high current. The transistor  52  is configured in the N-P-N configuration with the emitter coupled to ground. Accordingly, providing a positive voltage signal to the base of transistor  52  will bias the transistor  52  closed, coupling the base of transistor  52  to ground. 
   The base of transistor  50  is also coupled to the collector of transistor  52  and is therefore responsive to the voltage signal at the collector of transistor  52 . As is seen in the waveform diagrams of  FIGS. 5   a - 5   c , when the microprocessor  32  provides a pulse voltage signal to the Sensor Preheat Module  20  through the P0.1 pin, the transistor  52  is biased closed and the voltage at the collector is coupled to ground. Because the transistor  50  is in a P-N-P configuration, when the voltage at the base of transistor  50  is coupled to ground via transistor  52 , the transistor  50  is biased closed, coupling the emitter and collector and providing a steady voltage to the Sensor Module  22 . The pulsed output signal sent by the microprocessor  32  controls the operation of transistors  50  and  52  to provide a 0.9V equivalent DC voltage to the Sensor Module  22 . 
   In a preferred embodiment of the present invention, the Sensor Module  22  comprises a tin dioxide semiconductor gas sensor  54 . Tin dioxide sensors have high sensitivity to the presence of alcohol, however, it is contemplated that other suitable gas sensors are available and can be utilized in the present invention. The sensor  54  comprises a heating element  56  and a sensor element  58 . The heating element  56  comprises a resistor having a first end coupled to the voltage output of the Sensor Preheat Module  20  and a second end coupled to ground. The sensing element  58  comprises a variable resistor having a conductivity that varies depending on the temperature of the sensor and the concentration of alcohol vapors present. A tin dioxide gas sensor manufactured by FiS, Inc. of Japan and sold as Product No. SB-30 is utilized in a preferred embodiment of the present invention. 
   In order to obtain optimum performance from the sensor  54  the voltage applied across the heating element  56  must be held steady. The sensor  54  of the present invention exhibits optimum performance when a voltage of 0.9V is applied to the heating element  56 . As previously described, the components of the Sensor Preheat Module  20  are selected to provide a constant 0.9V to the heating element during operation of the breath test device  10  of the present invention. Reference point  60  is coupled to microprocessor  32  at P1.2/AD2/INT input/output pin (Port  3 ) to enable the microprocessor  32  to monitor the voltage at reference point  60 . The output signal representing the voltage at the sensing element  58  is measured at reference point  66  adjacent to load resistor  68  and is coupled to the microprocessor  32  at the P1.0AD0/INT input/output pin (Port  1 ) for monitoring by the microprocessor  32 . 
   In a preferred embodiment, the memory  70  of the Look-Up Reference Module  26  comprises an electrically erasable and programmable read-only memory (EEPROM) unit having at least 2048 bits of serial memory. An EEPROM suitable for use in the present invention is manufactured by Atmel Corp. and sold under Product No. AT2402C. The EEPROM  70  is used to store calibration data and look-up tables utilized by the microprocessor  32  during operation of the breath test device  10 . The EEPROM is coupled to +4V output of the step up voltage converter  44 . 
   The EEPROM  70  is used to store calibration and look-up table information used by the microprocessor  32  to calculate the blood alcohol content from the output voltage signal of the  20  sensing element  58 . The breath tester device  10  is calibrated prior to use and may be recalibrated with new calibration and look-up table information being entered at the programming unit  34  and stored on the EEPROM  70 . EEPROM  70  comprises a plurality of memory locations which serve as individually addressable reference registers containing values for the microprocessor to compare against the output of the sensing element during calibration and operation of the electronic breath analyzer. Data stored on the EEPROM  70  is clocked out to the microprocessor  32  at Serial Data (SDA) pin in response to receiving clocking input signals from the microprocessor  32  at the Serial Clock (SCL) pin. The SDA pin of the EEPROM  70  is coupled to the P2.2/S1 pin (Port  14 ) of the microprocessor  32 . The SCL pin of the EEPROM  70  is coupled to the P2.3 pin (Port  13 ) of the microprocessor  32 . The speed of the microprocessor  32 , and in turn the clocking signal generated by the microprocessor  32  and received by the EEPROM  70 , is determined by the oscillation of the crystal  72  of the Crystal Module  14 . It is contemplated that any suitable crystal can be used in the present invention. While in this embodiment of the present invention, the memory  70  is a separate component than the microprocessor  32 , it is contemplated that a microprocessor with sufficient internal memory can be utilized to perform the same functions as the separate memory and microprocessor configuration described herein. 
   The microprocessor  32  is also coupled to a Display Module  28 . In a preferred embodiment of the present invention, the Display Module  28  comprises a liquid crystal display (LCD)  74 . After performing the comparison of the data collected at reference point  60  against the date stored in EEPROM  70 , the microprocessor  32  will cause the appropriate output to be displayed on the LCD  74 . In the present embodiment, the LCD  74  displays the numeric value of the blood alcohol content of the user of the device  10 . The LCD  74  is also used to display messages to the user of the device  10 . 
   The circuit elements and arrangement described herein enables the breath tester device  10  of the present invention to address the need for a small, simple to use and convenient breath tester device. The circuitry can be packaged in a small housing to enable the breath tester to be extremely portable, such as a small attachment to key chain. The incorporation of the LCD results in the device conveying simple and clear instructions to the user of the device and simple and clear display of blood alcohol content. In addition, the selection of the specific electrical components described herein results in a system that works with minimal power requirements, prolonging the life of the power source and adding further to convenience of operation of the present device. 
   The foregoing description of an exemplary embodiment has been presented for purposes of illustration and description. It is not limited to be exhaustive nor to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiment described herein best illustrates the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.