Abstract:
A solid-state digital control and detection apparatus employs electronic sensors to create pulse signals, the width of which is determined by sensing values. The sensing pulses are then compared with setting pulses, the width of which is adjustable, in two types of comparison circuits. Result pulses from one of the comparison circuits are filtered for control and that from the other one are digitalized for display by using counters.

Description:
[0001]     This present application claims priority from U.S. provisional application No. 60/697,196 having the same tile as the present invention and filed on Jul. 7, 2005. 
     
    
     CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0002]     Not Applicable  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0003]     Not Applicable  
       REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX  
       [0004]     Not Applicable  
       FIELD OF THE INVENTION  
       [0005]     This invention relates to apparatus for acquiring from sensors the electric signals that are determined by the physical or chemical properties of an object, displaying the signal values, processing the signals, and creating control signals for actuation of responsive devices for controlling these properties of the object to predetermined desired values.  
       BACKGROUND OF THE INVENTION  
       [0006]     Sensors are used to convert the physical or chemical properties of an object to electrical signals such as voltage and current. A modern digital sensing apparatus normally comprises of sensors, a signal-processing unit that applies stimulus signals to the sensors if necessary, and amplifies, filters the signals acquired from the sensors, an Analog to Digital (A/D) device that converts the analog signals to digital signals, and a communication unit that receives inquiry commands and sends out sensing data to a computer.  
         [0007]     Basically, an A/D device is used to compare the input voltage to a reference voltage to convert voltage level signals to digital signals. To obtain an accurate result, a high precision and stable reference voltage source is needed, and the input voltage change in sampling should be minimized. As a result, for passive sensors that do not generate electrical signals, e.g. resistive sensors and capacitive sensors, a dedicated voltage or current stimulus source is required, and sometimes a complex signal stimulus and signal processing circuit should be implemented. For example, for capacitive sensors, usually a square wave or sine wave generator is used to provide the alternate current stimulus, and the output signals are rectified to generate a low frequency signal, the level of which changes with the sensor capacitance.  
         [0008]     In this invention, a sensor interface circuit, which converts the sensing values directly to digital signals without using A/D devices, is presented. In the presented sensor interface circuit, pulse width, which is determined by the sensing values, rather than voltage level is used for digital signal conversion. Since no voltage level signals are employed for comparison and reference, the circuits are insensitive to the change or fluctuation of voltage supply. For example, if CMOS devices are used, the circuit can work in a voltage range of 3V to 18V. Based on that, a controller can be constructed either by using the digital sensing values or by directly comparing the sensing pulse with a value setting pulse.  
         [0009]     It is an object of the present invention to provide digital sensing, control, and communication circuits that are not sensitive to changes or fluctuation of voltage supplies.  
         [0010]     A second object is to provide a sensor interface circuit that needs not a dedicated conditioning circuit converting the signals from the sensor to appropriate signals for the A/D device; therefore, the circuit is simplified.  
         [0011]     Another object is to provide a compact digital sensing and control circuit that is able to work without employing microcontrollers or microcomputers. Thus, products based on the circuits can re-use small-scale logic devices from old computers to reduce pollution to environment.  
       BRIEF SUMMARY OF THE INVENTION  
       [0012]     The apparatus of the present invention, for signal acquirement, display, communication, and control, comprises electronic means for sensing the properties of an object, means for creating electronic signals relating to the measure of the sensed properties within a sensitivity range, electronic means for processing the signals for display, electronic means for displaying the signal values, electronic means for receiving commands from a computer or an analog controller, and sending signal values to a computer, electronic means for processing the signals acquired from the sensors to create therefrom control signals for actuation of responsive devices to control the properties of the object to predetermined desired values.  
         [0013]     To acquire signals from sensors, in the present invention, pulse width comparison, which includes a sensing pulse, the width of which changes with the sensing values, and a setting pulse, the width of which is adjustable by using either digital means (e.g. counters) or analog means (e.g. resistors or capacitors), is used. The means for sensing pulse generation uses mono-stable multi-vibrator, while either the digital pulse generation that includes an oscillator and a counter, or the mono-stable multi-vibrator can be used for setting pulse generation.  
         [0014]     Two types of pulse comparison are presented. One is used for control. Signals generated by the pulse comparison pass through a time-delay circuit, which is employed to prevent rapid on/off cycling, and the result control signals are then used to control the responsive device. The other type of pulse comparison is for digitalization. Signals through the pulse comparison are converted to digital signals by using a counter, and a low pass digital filter is used to decrease the effects of high frequency noise. The result digital signals are then sent to a display or a digital controller.  
         [0015]     The circuits described in the present invention can be integrated into a dedicated IC for sensor interface and control. Since no A/D is needed, and no complex computation is necessary, the IC can be low-cost. On the other hand, all the circuits in the present invention can also be realized by using small-scale logic devices such as 74HC series, 4000 series. Thus, products based on the circuits described in this invention can reuse small-scale logic devices from old computers to reduce pollution to environment.  
         [0016]     Other features and advantages of the invention will be apparent from the following description, including accompany drawings, of illustrative embodiments thereof. 
     
    
     BIREF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a block diagram schematically showing the relation of the functional circuit sections (including control, display and communication) in the present invention;  
         [0018]      FIG. 2  is a schematic diagram of a humidity controller embodying the present invention;  
         [0019]      FIG. 3  is a timing diagram of the apparatus in  FIG. 2 ;  
         [0020]      FIG. 4  shows the waveform of the time-delay circuit in  FIG. 2 ;  
         [0021]      FIG. 5  is a schematic diagram of a display and communication circuit embodying the present invention;  
         [0022]      FIG. 6  is a timing diagram of the apparatus in  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     The present invention includes three functions: control, display, and communication. Referring to  FIG. 1 , a sensor  101  is connected to a pulse generation circuit  102  that is used to generate a pulse, the width of which changes with sensing values. In the display and communication block  130 , this sensing pulse is compared with a pulse generated by the reference pulse generation circuit  103  in a pulse comparison unit  105 , and therein the pulse width is adjusted according to the sensing range. The output pulse from the unit  105  is then digitalized in a circuit  114  by using an oscillator  113  and filtered through a circuit  107 . The result digital signals are displayed through a device  108 . Either the pulse signals generated by the pulse comparison circuit  105  or digital signals from the filter  107  can be sent to a circuit  109  for communication.  
         [0024]     In a control block  120 , a control pulse is generated by a circuit  104 , and compared with the sensing pulse from the circuit  102  in a pulse comparison unit  106 . The result pulse from the unit  106  is then filtered through a circuit  110 , and used to control an on/off controller  111 , which is employed to control a responsive device  112 . In addition to the control pulses from the filter  110 , the response device  112  can also be controlled by the signals generated by a control circuit  116  based on the control setting input from a circuit  115  and the digital sensing signals from the filter  107 .  
         [0025]     An example of the controller  120  depicted in  FIG. 1  is a relative humidity controller illustrated in  FIG. 2 . Since the pulse processing is insensitive to power supply, a simple AC/DC converter circuit  220  is used to provide a DC voltage VCC for the controller and a synchronous pulse for the sensor pulse generation and reference pulse generation. The waveforms at points A and B are shown in  FIG. 3 . Alternate sinusoidal wave from the power line (point A) is converted to synchronous pulses, the amplitude of which is determined by the zener voltage of the zener diode in the converter  220 .  
         [0026]     The sensor for this controller can be either a resistive sensor or a capacitive sensor. If a capacitive sensor  202  is used, then a resistor  201  will be used with the sensor to generate a pulse (the width of which changes with the sensing values) through a mono-stable multi-vibrator  203 . The reference pulse is generated by a mono-stable multi-vibrator  211 , and the pulse width is set by using a capacitor  210  and a potentiometer  209 . Pulse D and E from the mono-stable multi-vibrators are compared in a D-type flip-flop  204 . If a positive coefficient sensor is used, then when the width of pulse D is shorter than pulse E, the environmental humidity is lower than the setting value. As shown in  FIG. 3 , in this situation, through the D-type flip-flop  204 , a high level signal will be generated at point G, which is used to turn on a humidifier through a RC low-pass filter including a resistor  205  and a capacitor  206 , a Schmitt trigger  207 , and an on/off humidifier control circuit  208 . The waveforms at G and two ends of the Schmitt trigger, K and L, are depicted in  FIG. 4 . The high level signal at G charges the capacitor  206  through the resistor  205 . A high level “on” signal is not generated at L until the voltage at K is higher than the high threshold of the Schmitt trigger  207 . When the environmental humidity is higher than the setting value, a low level signal appears at G. If the low level signal persists longer than the time set by the resistor  205  and the capacitor  206 , then the humidifier will be turned off. When the humidity hovers at the setting value, short pulses may appear at G. The humidifier can only be turned on when the charge accumulated in the capacitor  206  is enough to make the voltage at K higher than the high threshold of the Schimitt trigger  207 , and be turned off when voltage at K is lower than the low threshold. Accordingly, by using this method, quick on/off is avoided by setting the minimum on/off time using the resistor  205  and the capacitor  206 .  
         [0027]     If only a humidifier or de-humidifier is used, then by using the low-pass filter and the Schmitt trigger, quick on/off can be avoided without setting a humidity hysteresis, i.e. the humidifier or de-humidifier is turned on and off at the same humidity, thus, the humidity can be controlled accurately at a value. However, if both a humidifier and a de-humidifier are used simultaneously, then to prevent the two devices working at the same time, a humidity hysteresis is needed. The hysteresis in  FIG. 2 . is realized by using an mono-stable multi-vibrator  219 , with a resistor  217  and a capacitor  218  setting an extra pulse, the width of which is longer than the minimum off time of the humidifier control set by the resistor  205  and the capacitor  206 . The extra pulse and the reference pulse from the mono-stable multi-vibrator  211  are then compared in a D-type flip-flop  212 . As shown in  FIG. 3 , the result control signal level at H will not be high until the humidity sensing pulse at C is longer than that of the reference pulse plus the extra pulse. The D-type flip-flop  212  is followed by a time-delay circuit including a resistor  213 , a capacitor  214 , and a Schmitt-trigger  215 . And the filtered control signal from the Schmitt trigger  215  is sent to a circuit  216  for dehumidifier control.  
         [0028]     An example embodying the display and communication block  130  depicted in  FIG. 1  is shown in  FIG. 5 . This circuit can be used to filter and display the values acquired from a capacitive sensor. Due to the pulse processing nature, this circuit is insensitive to the voltage supply. Therefore, a simple AC/DC converter  330  is used. The converter  330  provides power supply and synchronous pulses for the circuit. A capacitive sensor  302  and a resistor  301  are connected to a mono-stable multi-vibrator  303 , and used to set the pulse width that changes with the sensing value. The sensing pulse is then compared with a setting pulse that is generated by using a capacitor  307 , a resistor  306 , and a mono-stable multi-vibrator  308  in an AND gate  304 . The pulse comparison is used to zeroize the reading.  
         [0029]     The AND gate  304  is connected to the counters, the clock of which is provided by an oscillator  309 , and the reset logic is controlled by a control logic circuit  320 . Synchronous pulses of the circuit  320  are provided by the AC/DC converter  330  through a frequency divider  313 , where the frequency of the synchronous pulses is divided by a number m. As an example of the counter circuit, two counters,  305  and  310  are drawn in  FIG. 5 . The carry output (CO) of the counter  305  is connected to the carry input (CI) of the counter  310 . Thus, Q 0  of the counter  305  is the least significant bit, while Qn of the counter  310  is the most significant bit, provided that Q 0  is the least significant bit of the counters. The outputs Q 0  to Qn of the counter  310  are connected to a display circuit, the logic of which is also controlled by the control logic circuit  320 . When binary counters are used, in the counter circuit, the frequency of the oscillator should be ƒ, 
 
ƒ=2 kn /( mT ), 
 
         [0030]     where T is the sensing pulse width corresponding to the full scale of the sensor, and k is the number of counters (k=2 in this example). If BCD (Binary Coded Decimal) counters are used, then 
 
ƒ=10 kn/4 /( mT ). 
 
         [0031]     For example, if the counters  305  and  310  are two 2-decade BCD counters (n=8), and a 2-decade BCD counter is used for the frequency divider  313  (m=100), the frequency of the oscillator then should be 100/T. If a capacitive relative humidity sensor is used as the sensor  302 , and the capacitances corresponding to 100% and 0 are, respectively, C max  and C min , then the frequency of the oscillator  309  is 100/[g(RC max )−g(RC min )], where R is the resistance of the resistor  301 , and g(RC) is a function determined by the mono-stable multi-vibrators (e.g. for 74HC221, g(RC)=0.7 RC). In this example, if the counters  305  and  310  are reset and enabled with high level, then the control logic in the circuit  320  can be:  
         [0032]      313 Pulse 99 = 313 Q 0  AND  313 Q 3  AND  313 Q 4  AND  313 Q 7 ,  
         [0033]      313 Pulse 98 =(NOT  313 Q 0 ) AND  313 Q 3  AND  313 Q 4  AND  313 Q 7 ,  
         [0034]      305 Reset= 310 Reset= 313 Pulse 99  AND  308 Q,  
         [0035]      305 Enable= 310 Enable= 303 Q AND  308   Q ,  
         [0036]     DisplayLatch= 313 Q 98  AND  303 Q,  
         [0037]     where  313 Q 0 ,  313 Q 1 , . . . ,  313 Q 7  are, respectively, the ouput bit 0  to bit 7  (not shown in the figure) of the divider  313 ;  303 Q is the sensing pulse output b of the mono-stable multi-vibrator  303 ;  308 Q and  308   Q  are the setting pulse outputs of the mono-stable multi-vibrator  308 ;  305 Reset and  306 Reset are the Reset inputs of the counters  305  and  310 , while  305 Enable and  310 Enable are the Enable inputs which enable the counting; DisplayLatch is a control signal line that can be used to latch the digital output signals into the display register. In this example, a falling edge signal is provided for the DisplayLatch. (A rising edge signal can be obtained through an inverter.)  
         [0038]     The timing diagram of this circuit example is illustrated in  FIG. 6 . The setting pulse at  308 Q is synchronized by the pulses output from the frequency divider  313 . At pulse  99 ,  313 Pulse 99  is 1 (high level). With the rising of the  313 Q pulse, the counters  305  and  306  are reset to 0 when the reset pulse appears on  305 Reset and  310 Reset. At the falling edge of the reset pulse, the counters  305  and  310  are enabled by the adjusted sensing pulse (Enable pulse), the pulse width of which is the difference between the sensing pulse and the setting pulse. The counters  305  and  310  accumulate the counts for the width of adjusted sensing pulses, and a display latch pulse is generated at synchronous pulse  98 . The falling edge of this display latch pulse is used to latch the output of the counter  310  to the register of a display (not shown in the figure). Since the counting for the width of adjusted sensing pulses starts at the synchronous pulse  99 , the width of 100 adjusted sensing pulses will be accumulated in the counters before reset. The frequency of the oscillator is selected to be 100/T, therefore, at each adjusted sensing pulse i, the count in the counters  305  and  310  will increase 100T i /T, where T i  is the pulse width. At the synchronous pulse  99 , the output of the counters  305  and  310  before reset is  
         ∑     i   =   1     100     ⁢     100   ⁢       T   i     /     T   .             
 
 Connecting only the counter  310  to a display  311 , then the display value is the output of the counter  310 ,  
           ∑     i   =   1     100     ⁢     100   ⁢       T   i     /   T         100       
 
 , which is the average pulse width of 100 pulses in a resolution of two digits, thereby, a filter is implemented. The filter is able to remove high frequency disturbance, and is important to steady reading of sensor values. 
 
         [0039]     Both of the adjusted sensing pulse (e) and the digital signals for the display  311  can be used for communication. For the adjusted sensing pulse (e), a simple communication circuit  340  is used. In this circuit, the command is the Output Enable, the high level (or low level) enables the pulse signals to appear at the Out port. A communication circuit  312  is connected to the digital signals for the display  311 . Either a serial communication or a parallel communication can be employed.  
         [0040]     In summary, in the present invention, the pulse signals, the width of which is determined by the sensing values, are digitalized for display and used for control without A/D conversion. The circuits based on this invention are simple and insensitive to the supply voltage. In addition to being integrated into an IC, the circuits can also be realized by using small-scale logic devices such as 74HC series, 4000 series. Thus, products based on the circuits described in this invention can reuse small-scale logic devices from old computers to reduce pollution to environment.