Abstract:
Apparatus for simulating a candle flame in which the current through the filament of a bulb is varied from a first value to a second value and back to the first value during spaced periods that vary from a period of maximum duration to a period of minimum duration that produces no observable flicker in an apparently random manner.

Description:
This application is a continuation of application Ser. No. 08/271,171, filed Jul. 7, 1994, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     There are a number of situations where a candle is impracticable or too expensive. It would, for example, be impractical to use a candle for votive purposes in a cemetery, and in some places fire safety regulations would prevent it. Although candles are often used at dining tables in a restaurant, they are very expensive. 
     BRIEF SUMMARY OF THE INVENTION 
     Therefore, in accordance with this invention, an electrical candle is provided that simulates the flickering flame of an actual candle. An electrical circuit generates a control signal for varying the brightness of light emitted by a light emitting means between a first level and a second level and back to the first level during spaced periods of gradually increasing duration followed by periods of gradually decreasing duration, there being a number of periods of such short duration as to cause no noticeable change in brightness. In accordance with an aspect of this invention a suitable control signal may be derived by means including a first oscillator for producing waves at a given frequency, means including a second oscillator for producing waves at a slightly different frequency and means for increasing or decreasing the brightness of the light during times when the output waves of the first and second oscillators have like or unlike polarities respectively. The waves produced by the oscillators can be of any shape including sinusoidal or rectangular. 
     In accordance with this invention there are preferred operating parameters that the variations in brightness should meet in order to most effectively simulate the flame of a candle. 
     The change in brightness from a first level to a second and back to the first so as to produce a flicker during successive periods should occur at a rate between two and ten Hz with rates between four and one-half Hz and six Hz inclusive being preferred. When the first level is lower than the second, the flicker is an increase in brightness during the spaced periods, herein referred to as a positive flicker. This is preferred to the first level being higher than the second so as to produce a reduction in brightness during the spaced periods, herein referred to as a negative flicker. Furthermore, it is preferable that there be a ten to twenty percent change in brightness between the levels so that the light is not turned on and off because this tends to produce blinking rather than flickering. A blinking effect is also avoided by making the changes in brightness occur in a random manner or in a sequence that appears to be random. 
     It is important that the durations of the periods vary from one having the longest duration to one having minimum or no duration in a time between seven and thirty seconds, with fifteen seconds being preferred. The closer the frequencies of the two oscillators the longer it takes to go from a period of maximum duration to one of minimum duration, and the best simulation occurs when there is at least one period in each sequence during which there is no apparent flicker. 
     An electronically simulated candle of this invention can be energized by a battery so as to be easily moved about or it can obtain its energy by being plugged into an A.C. power outlet. 
     In accordance with another aspect of the invention, it is preferable that the light emitting means be an incandescent bulb that has the generally conical shape of a candle flame. A bulb that provides excellent simulation is about one and one half inches in height so as to approximate the height of a candle flame and has blue at its base and black lines extending part way up from the base so as to simulate a wick. For best results, the bulb should be translucent. If a bulb of clear glass is used, the simulation is improved by placing a translucent enclosure over the bulb that is preferably shaped like a candle flame and has the dark or blue base and the black lines simulating a wick. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings corresponding components are designated in the same way. 
     FIG. 1 is a schematic diagram of a preferred circuit for deriving a control signal of this invention; 
     FIGS. 1A,  1 B and  1 C are waveforms used in explaining how the embodiments of FIGS. 1 and 2 generate a control signal; 
     FIG. 2 is a schematic diagram of another circuit for deriving a control signal of this invention; 
     FIG. 3 is a circuit for energizing a bulb with A.C. in response to a control signal of this invention; 
     FIGS. 4A and 4B illustrate an incandescent bulb constructed so as to aid in simulating a candle; and 
     FIG. 5 shows a candle incorporating the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is made to the schematic diagram of FIG. 1, which shows a circuit comprised of two chips  2  and  4  in rectangles formed by dashed lines that, for example, may be  4011 &#39;s. The chip  2  is comprised of four NAND gates  6 ,  8 ,  10  and  12 . The NAND gates  6  and  8  are coupled so as to form a first multivibrator oscillator  14  that outputs square waves such as those illustrated in FIG. 1A, for example. In the particular embodiment shown, the coupling is comprised of a capacitor  16  having one side connected to the output  18  of the NAND gate  8 , a variable resistor  20  and a resistor  22  connected in series between the other side of the capacitor  16  and the inputs  24  and  26  of the NAND gate  8  and a resistor  25  connected between the other side of the capacitor  16  and inputs  27  and  28  of the NAND gate  6 . 
     The chip  4  is comprised of four NAND gates  30 ,  32 ,  34  and  36  the NAND gates  30  and  32  are coupled so as to form a second multivibrator oscillator  38  that outputs the square waves such as those illustrated in FIG. 1B, for example, that have a slightly lower frequency than those of FIG.  1 A. In the particular embodiment shown, the coupling is comprised of a capacitor  40  having one side connected to the output  42  of the NAND gate  32  and resistors  44  and  46  that are respectively connected between the other side of the capacitor  40  and the inputs  48  and  50  of the NAND gate  32  and the inputs  52  and  54  of the NAND gate  30 . 
     The output  18  of the NAND gate  8  where the square waves of FIG. 1A that are produced by the first multivibrator  14  appear, and the output  42  of the NAND gate  32  where the square waves of FIG. 1B that are produced by the second multivibrator  38  appear are connected to respective inputs  56  and  58  of the NAND gate  34 , and its output  60  is connected to both inputs  62  and  64  of the NAND gate  10  to effectively make an AND gate of the combination of the NAND gate  34  and NAND gate  10  and produce a control signal such as illustrated in FIG. 1C at its output  66 . Notice that, as in an AND gate, the control signal of FIG. 1C is high only when both the square waves of FIGS. 1A and 1B are high. 
     The light emitting means is herein indicated as being an incandescent bulb  68  having a filament  70 . A means for controlling the brightness of the light emitted from the bulb  68  in accordance with the control signal of FIG. 1C that appears at the output  66  of the NAND gate  10  is now described. A power supply  72  that derives D.C. voltage from an A.C. source, not shown, is connected in series with the filament  70  and the collector/emitter path of a transistor  74 , and a resistor  76  is connected in parallel with the collector/emitter path. The control signal at the output  66  of the NAND gate  10  is coupled to the base electrode  78  of the transistor  74  via a current limiting resistor  80  in order to protect the transistor  74 . When the transistor  74  is not conducting, the current through the filament is less than maximum by an amount determined by the value of the resistor  16   76 so that the brightness of the light is at a level less than maximum, but when the transistor  74  is conducting, it shorts the resistor  76  so as to permit maximum current to flow through the filament  70  and increase the brightness of the light from the bulb  68  to a maximum level. 
     Power is supplied to the IC&#39;s  2  and  4  from a junction  82  of a resistor  84  and a capacitor  86  that are connected in series between the output of the power supply  72  and ground. This permits the power supply  72  to be marginally filtered and therefore less expensive. 
     A resistor  88  is connected between the junction  82  and the output  66  of the NAND gate  10  in order to balance the current that the IC  2  draws when it is sourcing current to the transistor  74  compared to when it is not sourcing that current and thus prevent the control signal of FIG. 1C from appearing as a ripple at the junction  82 . The resistance of the resistor  88  is preferably the same as the resistance of the resistor  80 . 
     If the balancing resistor  88  is not used, additional current is drawn through the resistor  84  when the output  66  is high because of the base current supplied to the transistor  74 . This causes a slight reduction in the supply voltage at the junction  82  for the IC&#39;s  2  and  4 . This additional current is not drawn when the output  66  is low so that the voltage at the junction  82  is not reduced. A ripple voltage thus appears at the junction  82  that can cause the oscillators  14  and  38  to lock to the same frequency and cause the light  68  to blink rather than flicker. 
     The operation of the circuit just described for simulating a candle is now described with reference to the waves of FIGS. 1A,  1 B and  1 C. The output of the NAND gate  34  becomes a low when the respective outputs  18 , FIG. 1A, and  42 , FIG. 1B, of the multivibrators are both a high and is inverted by the NAND gate  10  so as to produce the wave of FIG. 1C, which is the control signal. The relative frequencies of the multivibrators can be changed by altering the value of a circuit component of one of them. In the example shown, the resistor  20  is variable so that the frequency of the first multivibrator  14  can be changed. If the frequency of this multivibrator is made greater than the frequency of the multivibrator  38 , waves such as indicated in FIGS. 1A and 1B appear at the outputs  18  and  42  respectively. 
     When the waves of FIGS. 1A and 1B are both positive, the control signal of FIG. 1C is positive so as to cause the transistor  74  to conduct, thereby increasing the brightness of the light emitted from the bulb  68  due to the shorting of the resistor  76 . This increase in brightness is referred to as positive flicker. During the low levels of the control signal of FIG. 1C, the transistor  74  does not conduct so that the brightness of the light  68  is at its lower level. Note that the waves of FIGS. 1A and 1B start out in what appears to be an in phase condition. Actually, however, the frequencies are slightly different so that saying that the waves are in phase is technically inaccurate. Nonetheless, it is true, that both waves are high during the entire high pulse output  90  of the higher frequency multivibrator  14  shown in FIG. 1A so as to produce a pulse  92  in FIG. 1C having a maximum duration. As time goes on, the durations of successive pulses in FIG. 1C become less until a point  94  is reached where there is no positive pulse and consequently no change in the brightness of the bulb  68  when one would be expected. That no positive pulse is produced is explained by noting that the longer negative pulse  94   1  FIG. 1B straddles the positive pulse  94   11  of FIG.  1 A. Furthermore, if the frequencies of the oscillators  14  and  38  are close enough together, for example, 5 Hz and 5.066 Hz respectively, the pulses for about one second on both sides of a point such as  94  are of such short duration as to increase the energy supplied to the filament  70  so slightly that there is very little if any noticeable change in the brightness of the light it emits, thereby ensuring that the absence of flicker is clearly noticeable. The frequencies represented by FIGS. 1A and 1B are much farther apart than 0.066 cycles a second so that only a few pulses such as  95  and  97  have the short duration referred to. An absence of noticeable flicker is important to the simulation. 
     The time between maximum and zero pulse duration, or between maximum and minimum positive flickers, depends on the difference between the frequencies of the multivibrators  14  and  38  and should be between seven and thirty seconds, preferably fifteen seconds. With the frequencies mentioned above, the time between a maximum brightness such as would occur during the pulse  90  and minimum brightness as would occur at the point  94  is 15 seconds. The frequency of the flicker is five cycles a second so as to be within the desired range of 4.5 to 6.0 Hz. 
     Note that the intervals between flickers are, for the most part, greater than the flicker durations themselves and that the intervals between flickers gradually increase and decrease so as to imitate a candle flame. Although not preferred, the polarity of the control wave of FIG. 1C could be inverted by eliminating the NAND gate  10  and using the wave at the output  60  of the NAND gate  34  as the control signal. This would cause the maximum brightness to occur during longer periods of time that are separated by shorter intervals during which the brightness is reduced to a lower level. This is referred to as a negative flicker, but the positive flicker previously described is preferred. 
     In order to permit the output of the multivibrator  14  to be shown on an oscilloscope without affecting its operation, the inputs  96 ,  98  of the NAND gate  12  are connected to the output  18  of the first multivibrator  14 , and in order to permit the output of the multivibrator  38  to be shown, the inputs  100 ,  102  of the NAND gate  36  are connected to the output  42  of the second multivibrator  38 . When an oscilloscope or other instrument is coupled to an output  104  of the NAND gate  12  or to the output  106  of the NAND gate  36 , it is decoupled from the respective multivibrator so as not to affect its operation. 
     Reference is now made to FIG. 2 that illustrates a less expensive circuit for generating a control signal like that of FIG. 1C in which the multivibrators are on the same chip  107 , e.g., a CD4069. This operates as desired unless the oscillators become locked through stray coupling within the CD4069 IC. A first multivibrator  108  that produces an output like FIG. 1A is shown as being comprised of inverters  110  and  112  that are connected in series. One side of a capacitor  114  is connected to the output  116  of the inverter  112 , and the other side is respectively connected to the inputs of the inverters  110  and  112  via resistors  118  and  120 . The output  116  of the inverter  112  is connected to the input of an inverting buffer  122  so as to produce a signal like that of FIG. 1A at its output  123 . A second multivibrator  124  that produces an output like FIG. 1B is comprised of inverters  126  and  128  that are connected in series. One side of a capacitor  130  is connected to the output  132  of the inverter  128 , and its other side is connected via a resistor  134  and a variable resistor  136  to the input of the inverter  128  and via a resistor  138  to the input of the inverter  126 . The output  132  of the inverter  128  is connected to the input of an inverting buffer  139  so as to produce a signal like FIG. 1B at its output  140 . The frequency of the wave of FIG. 1B can be varied by adjusting the value of the resistor  136 . 
     The means for controlling the brightness of a light and the power supply for the light and for the circuits are the same as in FIG. 1, and the components thereof are designated in the same manner. The control signal of FIG. 1C is made to appear at the base electrode  78  of transistor  74  as follows. The output  123  of the buffer inverter  122 , where the wave of FIG. 1A appears, is coupled in series with a diode  142  to the base electrode  78  of the transistor  74 . The output  140  of buffer inverter  139 , where the wave of FIG. 1B appears, is coupled via the current limiting resistor  80  to the base electrode  78 . The diode  142 , the resistor  80  and the base  78  meet at a junction  141 . 
     The operation of FIG. 2 is as follows. The buffer inverters  122  and  139 , the resistor  80  and the diode  142  form a discrete component AND gate supplying voltage to the base  78  of transistor  74 . When the output  140  of buffer inverter  139  and the output  123  of buffer inverter  122  are high, the base  78  of transistor  74  will be high and the transistor  74  will conduct. If the output of buffer inverter  139  or the output of the buffer inverter  122  is low, the base  78  of the transistor  74  will be low and the transistor will not conduct. The wave that appears at the base electrode  78  of transistor  74  is shown in FIG.  1 C. The balancing resistor  88  can be connected on either side of the current limiting resistor  80 . 
     It is contemplated that the D.C. power supply  72  in FIGS. 1 and 2 could be a battery in which case the filter comprised of the resister  84  and the capacitor  86  as well as the balancing resistor  88  could be eliminated. 
     Reference is now made to FIG. 3 for a description of a circuit for energizing the “candle” of this invention with A.C. power in response to a control signal like that shown in FIG.  1 C. All of the light control circuitry coupled to respond to the control signal at a junction  143  of FIG. 1 or the junction  141  of FIG. 2 is eliminated, and the following circuitry is substituted for it. 
     D.C. operating voltage for the chips  2  and  4  of FIG. 1 or for the chip  107  of FIG. 2 is derived by coupling a source  144  of A.C. voltage between a grounded terminal  146  and a rectifying circuit comprised of a resistor  148 , a diode  150 , a capacitor  152  and a zenor diode  154  connected as shown. The D.C. operating voltage for the chips  2  and  4 , or  107 , is at the junction  156  of the diode  150  and the zenor diode  154 . 
     Energization of a filament  158  of a lamp  160  in response to the control signal like that of FIG. 1C that is at the junction  143  of FIG. 1 or at the junction  141  of FIG. 2 so as to produce a candle-like flicker in accordance with this invention is attained as follows. The filament  158  is connected in series with a resistor  162  and a capacitor  164  between the ungrounded side of the A.C. source  144  and the grounded terminal  146  so as to meet at a junction  163 . A triac  166  is connected between a junction  168  of the filament  158  and the resistor  162  and the grounded terminal  146 , and a bilateral trigger diac  170  is connected between the junction  163  of the resistor  162  and the capacitor  164  and the gate electrode  174  of the triac  166 . 
     The circuit thus far described in the paragraph immediately above operates as a conventional incandescent light dimmer in which the resistor  162  and capacitor  164  are a single-element phase-shift network. When the voltage across capacitor  164  reaches the breakover voltage of diac  170 , the capacitor  164  is partially discharged by the diac  170  into the gate  174  of the triac  166 . The triac  166  is then triggered into the conduction mode for the remainder of that half-cycle. Selection of the resistance value of resistor  162  adjusts the amount of phase shift at gate  174  and determines the point in the A.C. half-cycle at which the triac  166  triggers into the conduction mode. The point in the half cycle at which triac  166  starts to conduct determines the RMS voltage across filament  158  that determines the minimum brightness of lamp  160 . 
     In accordance with this invention, a triac  176  is connected between the junction  168  and the control electrode  174  of the triac  166  via a current limiting resistor  178 . The control electrode  180  of the triac  176  is connected to a terminal  145  via a current limiting resistor  182 . The terminal  145  would be connected so as to receive the control signal at the junction  143  of FIG. 1 or the junction  141  of FIG. 2. A current balancing resistor  183  for preventing a ripple from appearing at the voltage supply terminal  156  is connected between the terminals  145  and  156 . While the control signal, FIG. 1c, is high, the triac  176  conducts so as to make the control electrode  174  of the triac  166  high, thereby causing current to flow through the filament  158  during entire alternate half cycles of the voltage from the source  144 . The effect of the phase shift network comprised of the resistor  162  and the capacitor  164  is therefore eliminated, and a positive flicker is produced whenever the control signal of FIG. 1C is high. 
     Square waves such as shown in FIGS. 1A, and  1 B could be derived in other ways such as by clipping the output of a sine wave oscillator. Alternatively, the outputs of sine wave oscillators could be applied to the inputs of a NAND gate or an AND gate. 
     Reference is made to FIGS. 4A and 4B for a description of physical features of the bulb  68  which, in accordance with an aspect of the invention, contributes to the simulation of a candle flame. The bulb  68  is preferably formed from frosted glass or may be a clear bulb with a frosted plastic cover, not shown. The lower portion  184  of the bulb  68  is dark, preferably blue, and the bulb  68  can be screwed into a socket as indicated at  186 . Dark lines  188 ,  190  and  192  extend part way up from the dark area  184  so as to simulate a wick. As best seen in the bottom view shown in FIG. 4B, the lines  188 ,  190  and  192  are preferably at 120° intervals. Because of the frosting, the filament  70  of the bulb would not be seen so that it is shown in broken lines. 
     FIG. 5 illustrates a candle constructed in accordance with this invention. A base  194  having a handle  196  supports a cylinder  198  containing, as indicated by dashed lines, the chips  2  and  4  and the associated circuitry of FIG. 1 as well as the transistor resistor combination  74 ,  76 . If the circuit of FIG. 2 is used, its chip  107  would be contained in the cylinder  198  in place of the chips  2  and  4 . The bulb  68  that is mounted at the top of the cylinder  198  is made of clear glass in this example and is shown by a broken line because it is within a translucent plastic cover  200  that is shaped like a candle flame. Making the cover  200  asymmetrical about the axis  199  of the cylinder  198  so as to appear to be twisted enhances the simulation of a flickering flame. Leads  202  and  204  are connected to a plug  206  that can be inserted in a power outlet so as to provide A.C. for the power supply  72  of FIGS. 1 and 2 or to be the supply  144  of FIG.  3 . If a battery is used, it is contained within the cylinder  198 , and the leads  202 ,  204  and the plug  206  are not required. 
     Although other values of components may be used, the following have been found to work well. 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 FIG. 1 
                 Chips 
                 4011 
               
               
                   
                   
                 R20 
                 200K 
               
               
                   
                   
                 R22 
                 820K 
               
               
                   
                   
                 R25, R46 
                 150K 
               
               
                   
                   
                 R44 
                 1 MEG 
               
               
                   
                   
                 C16, C40 
                 0.1 uf 
               
               
                   
                   
                 R76 
                 22 
               
               
                   
                   
                 R80 
                 10K 
               
               
                   
                   
                 R84 
                 4.7K 
               
               
                   
                   
                 R88 
                 10K 
               
               
                   
                 FIG. 2 
                 Chip 107 
                 CD4069 
               
               
                   
                   
                 R118 
                 750K 
               
               
                   
                   
                 R120, R138 
                 2M 
               
               
                   
                   
                 R134 
                 720K 
               
               
                   
                   
                 R136 
                 50K 
               
               
                   
                   
                 C108, C122 
                 0.1 uf 
               
               
                   
                 FIG. 3 
                 R148 
                 6.8K 1W 
               
               
                   
                   
                 R162 
                 1 MEG 
               
               
                   
                   
                 R178 
                 1K 
               
               
                   
                   
                 R182 
                 1K 
               
               
                   
                   
                 R183 
                 1K 
               
               
                   
                   
                 C152 
                 223 uf 
               
               
                   
                   
                 C164 
                 0.1 uf 
               
               
                   
                   
                 DIAC 170 
                 HT35 
               
               
                   
                   
                 TRIAC 166 
                 Q401E3 
               
               
                   
                   
                 TRIAC 176 
                 L401E3