JP2005092712A - Paper money identification apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that discrimination capability deteriorates with time. <P>SOLUTION: The paper money identification apparatus comprises an insertion port 21 of a bank bill 5; a passage 22; pulleys 23 and 24, rollers 26 and 27, and a transport belt 25 for transporting the paper money 5; a sensor part 46 provided on a wall surface of the passage 22; amplifiers 35 and 45 connected to the sensor part 46; an A/D converter 37; a frequency analyzer 38 connected to an output of the A/D converter 37; a memory 41; a comparator 39; and a decision unit 42. An output signal from the A/D converter 37 is Fourier transformed by the frequency analyzer 38, and the authenticity of the paper money 5 is discriminated on the basis of the Fourier transformed waveform. Thus, the paper money identification apparatus of which the discrimination capability does not deteriorate with time is obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a bill validator used for various automatic service devices such as vending machines and ticket vending machines.

  In recent years, with the diversification and increase in the price of commodities sold at vending machines, ticket vending machines, etc., banknote recognition devices that can use high-value banknotes other than thousand-yen banknotes have been widely used. In particular, devices that can use large bills are becoming common. On the other hand, with the progress of office automation equipment such as copiers and color printers, crimes that use counterfeit banknotes using these high-precision copiers are also on the rise. Therefore, it is necessary to prevent crimes.

  Hereinafter, the conventional banknote identification device will be described. FIG. 8 is a block diagram of a conventional banknote recognition apparatus. In FIG. 8, a red light emitting diode 2 and an infrared light emitting diode 3 are disposed in contact with one wall surface of the banknote transport passage 1, and a photodiode 4 is disposed on the other wall surface of the banknote transport passage 1. . With such a structure, when the bill 5 to be identified passes in front of the photodiode 4, the optical characteristics of the bill can be examined.

  Moreover, the conveyance means 6 (it is comprised from a belt and a roller here) which conveys the banknote 5 along the banknote conveyance path | route 1 is provided, and the banknote detection means 7 is arrange | positioned in the entrance of the conveyance means 6, and a banknote position Is connected to the control means 8. The red light emitting diode 2 and the infrared light emitting diode 3 provided in contact with the wall surface of the bill transport passage 1 are also connected to the control means 8 in order to emit light at an appropriate timing.

  The conveying means 6 is driven by a motor 9. The motor 9 is driven from the control means 8 via the motor drive circuit 10. Synchronous pulse generation means 11 connected to the motor 9 for detecting the rotation of the motor 9 is provided and connected to the control means 8.

  The output signal of the photodiode 4 is connected to the logarithmic amplifier circuit 12, and the output of the logarithmic amplifier circuit 12 is connected to the control means 8 via the linear amplifier circuit 13 and the AD conversion means 14. The reference current of the logarithmic amplifier circuit 12 is supplied from the control means 8 via the DA conversion means 15. Reference numeral 16 denotes reference value storage means, and 17 denotes input value storage means.

  Hereinafter, the operation of the conventional banknote recognition apparatus will be described. First, the state of each sensor is examined in a no-bill state when the bill recognition device is activated, and the optical sensor is normalized. First, the red light emitting diode 2 is caused to emit light. The output of the photodiode 4 is input to the control means 8 via the logarithmic amplifier circuit 12, the linear amplifier circuit 13, and the AD converter means 14. The control means 8 calculates the difference between the AD conversion value of the input voltage and a predetermined reference value Xr, and changes the input value Yr of the DA conversion means 15 with a constant conversion rate in a direction in which the difference becomes smaller. To do. The output of the DA conversion means 15 determines the reference current value of the logarithmic amplifier circuit 12. Therefore, the reference amplification factor of the logarithmic amplifier circuit 12 changes, and the output of the AD conversion means 14 (input value of the control means 8) can be made to coincide with a predetermined reference value Xr.

  Next, the infrared light emitting diode 3 is caused to emit light, similarly, the input value Yir of the DA conversion unit 15 is changed, the amplification factor of the logarithmic amplifier circuit 12 is adjusted, and the output of the AD conversion unit 14 is matched with the reference value Xir. .

  Since the standardization of the optical sensor is completed, the control unit 8 changes the input value of the DA conversion unit 15 in accordance with the light emission timing of each of the light emitting diodes 2 and 3, and thereby the respective light emitting diodes 2 and 3 are used. A predetermined sensitivity for a given wavelength is obtained.

  After the standardization of the optical sensor is completed as described above, when the banknote detection unit 7 detects the insertion of the banknote 5 at the entrance of the optical sensor unit, the control unit 8 activates the motor 9 to drive the conveyance unit 6, The bill 5 is drawn. The conveyance amount of the banknote 5 is measured by measuring the number of pulses generated by the synchronization pulse generation means 11 with the control means 8, and transports a predetermined distance from the banknote edge to the red light emitting diode 2 at a predetermined measurement point. Are obtained, and an AD conversion value Sr at that time and an AD conversion value Sir when the infrared light emitting diode 3 is caused to emit light next are obtained. The difference between the mounting positions of the red light emitting diode 2 and the infrared light emitting diode 3 is converted into the number of pulses generated by the synchronization pulse generating means 11 to correct the position so that data at substantially the same location is obtained.

  For banknote identification, numerical values such as the AD conversion value Sr of the red light emitting diode 2, the AD conversion value Sir of the infrared light emitting diode 3, and the difference Sr−Sir are obtained for a number of measurement points in the process of transporting the banknote 5. It is determined by the control means 8 whether or not the genuine bill is within a predetermined range, and comprehensive judgment is made together with the output of the magnetic sensor or the like to judge whether it is a genuine bill or a fake bill.

As prior art document information related to the invention of this application, for example, Patent Document 1 is known.
JP-A-8-7149

  However, in such a conventional bill discriminating apparatus, the analog amplitude information of the bill 5 output from the photodiode 4 is converted into logarithmic output amplitude information by the logarithmic amplifier circuit 12, and further the amplitude amplification proportional to the input by the linear amplifier circuit 13. After that, the A / D conversion means 14 converts it into a digital quantity, and compares the value of the reference value storage means 16 based on the amplitude quantity information to discriminate the banknote 5. Therefore, the amplitude amount information changes by about 20% due to a change with time of the light emitting diodes 2 and 3, adjustment of the logarithmic amplifier circuit 12, temperature change and linearity change of the linear amplifier circuit 13, and the like. There was a problem that the discrimination ability was lowered.

  The present invention solves this problem, and an object of the present invention is to provide a banknote recognition device in which the discrimination ability does not deteriorate due to the influence of a change over time or a change in humidity.

  In order to achieve this object, the bill discriminating apparatus of the present invention performs Fourier transform on the output signal from the A / D converter by a frequency analyzer and discriminates the authenticity of the bill based on the Fourier transform waveform. is there. As a result, it is possible to obtain a banknote recognition device in which the discrimination ability does not deteriorate due to the influence of changes over time and humidity.

  According to the first aspect of the present invention, there is provided a bill insertion slot, a passage connected to the insertion slot, transport means for transporting the bill inserted in the passage, and a wall surface of the passage. A provided sensor, an amplifier connected to the sensor, an A / D converter connected to the output of the amplifier, a frequency analyzer connected to the output of the A / D converter, and the frequency analysis An output of the comparator is connected to one input, a comparator to which a memory storing a reference value is connected to the other input, and a determiner to which the output of the comparator is connected, and the frequency An analyzer is a banknote discriminating device that Fourier-transforms the output signal from the A / D converter and discriminates the authenticity of the banknote based on the Fourier transform waveform, and the analog output from the sensor is converted into an A / D converter. To a digital quantity and then Fourier transform Since the amplitude information that has been input is converted into frequency information. Therefore, it becomes difficult to be influenced by amplitude information due to changes with time of the sensor and amplifier, and the discrimination ability is improved.

  In addition, since analog processing is performed instead of analog processing as in the prior art, it is less susceptible to noise and the like.

  Further, gain adjustment by the D / A conversion means of the logarithmic amplifier and a linear amplification circuit having excellent linearity are not required, and the circuit can be simplified and miniaturized.

  The invention according to claim 2 is the banknote identification device according to claim 1 which distinguishes engraving intaglio printing and dot printing with a Fourier transform waveform, and is converted into frequency information by Fourier transform. Can be reliably determined.

  Invention of Claim 3 is a banknote identification device of Claim 2 which discriminate | determines the authenticity of the banknote inserted by the characteristic of the waveform of 250 Hz to 1 KHz in a Fourier-transform waveform, Especially in this frequency band, The difference between engraving intaglio printing and dot printing appears remarkably. Therefore, it is possible to easily and reliably discriminate between genuine bills and counterfeit bills.

  Invention of Claim 4 is a banknote identification device of Claim 2 which discriminate | determines the money type of a banknote based on the Fourier-transform waveform in the specific position of a banknote, The specific position which shows the money type information of a banknote Since the denomination is discriminated based on the Fourier transform waveform in, the denomination of the banknote can be determined accurately.

  Invention of Claim 5 is a banknote identification device of Claim 1 which normalizes a Fourier-transform waveform with the passage time of a banknote, and since it has normalized with the passage time of a banknote, the error by a conveyance speed disappears. , Accurate discrimination.

  The invention according to claim 6 is the banknote identification device according to claim 1, which corrects the reference value by the output of the frequency analyzer, and can correct a change with time of a sensor or the like.

  The invention according to claim 7 uses an optical sensor and a magnetic sensor as the sensor, and discriminates a bill inserted based on signals output from the optical sensor and the magnetic sensor. Since the pattern printed on the banknote and the magnetic information are used, more accurate authenticity determination and denomination determination can be performed.

  According to an eighth aspect of the present invention, the sensor provided on the wall surface of the passage is composed of a light emitting diode and a photodiode for receiving a light emission output from the light emitting diode, and the light emitting diode is formed of only one color light emitting diode. It is the banknote identification apparatus of Claim 1 made | formed, and can identify a banknote only with the light emitting diode of 1 color by using a Fourier-transform technique. Therefore, it is possible to provide a bill recognition device that is small and inexpensive.

  In a ninth aspect of the present invention, the sensor provided on the wall surface of the passage includes a light emitting diode and a photodiode for receiving a light emission output from the light emitting diode, and the light emitting diode is formed of a red light emitting diode. It is a banknote identification device of claim | item 1, It can provide the banknote identification device which is hard to receive to the influence of the wrinkle of a banknote produced by using a banknote.

  In a tenth aspect of the present invention, the sensor provided on the wall surface of the passage includes a light emitting diode and a photodiode that receives a light emission output from the light emitting diode, and the light emitting diode includes a red light emitting diode including infrared light. The bill discriminating apparatus according to claim 1, which is formed as described above, and can use a light-emitting diode having high luminance at a low price, so that it is possible to provide a low-cost and high-performance bill discriminating apparatus.

  According to an eleventh aspect of the present invention, the sensor provided on the wall surface of the passage includes a light emitting diode and a photodiode that receives a light emission output from the light emitting diode, and the light emitting diode is formed of an infrared light emitting diode. The bill recognition device according to claim 1, wherein infrared light is used, so that not only bill recognition by infrared light but also magnetic printing can be detected, and accurate bill recognition can be performed only by a light emitting diode. It can be performed.

  According to a twelfth aspect of the present invention, the sensor provided on the wall surface of the passage includes a light emitting diode and a photodiode that receives a light emission output from the light emitting diode, and the light emitting diode is formed of a blue light emitting diode. Item 2. The banknote identification device according to Item 1, wherein the blue light-emitting diode has a short wavelength, and thus can detect a difference in transmittance due to paper quality. Therefore, not only the identification of the banknote by blue light but also the difference in transmittance due to the paper quality can be detected, and the accurate banknote identification can be performed.

  As described above, according to the present invention, the output signal from the A / D converter is Fourier-transformed by the frequency analyzer, and the bill discriminating device discriminates the authenticity of the bill based on the Fourier-transform waveform. Since the analog output from is converted into a digital quantity by an A / D converter and then subjected to Fourier transform, the input amplitude information is converted into frequency information. Therefore, it is less affected by amplitude information due to changes with time and humidity of the sensor and amplifier, and the discrimination ability is improved.

  In addition, since analog processing is performed instead of analog processing as in the prior art, it is less susceptible to noise and the like.

  Further, gain adjustment by the D / A conversion means of the logarithmic amplifier and a linear amplification circuit having excellent linearity are not required, and the circuit can be simplified and miniaturized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, reference numeral 21 denotes an insertion slot for the banknote 5, and reference numeral 22 denotes a passage for the banknote 5 provided in connection with the insertion slot 21. Reference numerals 23 and 24 denote pulleys provided on the bottom surface of the passage 22, and two conveying belts 25 are spanned between the pulleys 23 and 24 at both ends thereof. Reference numerals 26 and 27 denote rollers provided facing the pulleys 23 and 24, respectively, and conveys the bill 5 between the conveyance belt 25 and the rollers 26 and 27. The pulley 24 is a drive wheel and is connected to the motor 28. The motor 28 is driven by a signal from the control unit 30 via a motor drive circuit 29. The rotation of the motor 28 is connected to the control unit 30 via the synchronous pulse generator 31 and controlled.

  Reference numeral 32 denotes an entrance sensor. The entrance sensor 32 is provided at the entrance of the passage 22 and is connected to the control unit 30. A light emitting diode 33 is provided on the upper surface of the passage 22 and is connected to the control unit 30. A photodiode 34 is provided on the bottom surface of the passage 22 so as to face the light emitting diode 33, and is connected to the input of the amplifier 35.

  Here, a red light emitting diode is used as the light emitting diode 33 in the present embodiment. In the present invention, since the Fourier transform technology described later is used, it is possible to identify the banknote 5 sufficiently with only one color wavelength. Therefore, it is possible to provide a bill recognition device that is small and inexpensive. Moreover, since red has a long wavelength, it is possible to identify banknotes that are not easily affected by the wrinkles of banknotes caused by the use of banknotes.

  In order to increase the brightness of the red light emitting diode, a P layer or an N layer may be further added in addition to the PN junction of the light emitting diode. By doing so, the light emission luminance is improved and the bill recognition power is improved. At this time, an infrared color may be included in addition to red due to the addition of the P layer and the N layer. However, in the present invention, even if this infrared color is included, the banknote 5 can be identified by using the Fourier transform technique. That is, since a red light emitting diode including infrared light can be used as it is without using an infrared color filter or the like, low-cost and high-performance identification is possible.

  Further, as the light emitting diode 33, an infrared light emitting diode may be used. In this case, not only the banknote 5 can be identified by infrared light, but also the magnetism included in the banknote 5 can be identified. Accordingly, it is possible to accurately identify the banknote 5 including magnetic information.

  Further, as the light emitting diode 33, a blue light emitting diode may be used. Since the blue light emitting diode has a short wavelength, it is possible to detect a difference in transmittance due to the paper quality of the bill 5. Accordingly, not only the bill 5 can be identified by blue light, but also the transmittance of the bill 5 can be identified. Therefore, accurate bill 5 identification can be performed.

  As described above, the light emitting diode 33 may be an infrared light emitting diode or a blue light emitting diode in addition to red. In any case, the subsequent processing can be easily performed by using the light emitting diode 33 as a sensor. Also, a low price can be realized.

  The output of the amplifier 35 is connected to one terminal of the electronic switch 36. The electronic switch 36 can be realized by hardware or software. The common terminal of the electronic switch 36 is connected to the input of the A / D converter 37, and the output thereof is connected to the input of a Fourier transformer (used as an example of a frequency analyzer) 38. The output of the Fourier transformer 38 is connected to one input of the comparator 39 and also connected to the memory 41 via the correction circuit 40.

  The output of the memory 41 is connected to the other input of the comparator 39. The output of the comparator 39 is connected to the determiner 42, and the output is connected to the output terminal 43. A switching signal for the electronic switch 36 is output from the control unit 30.

  Reference numeral 44 denotes a magnetic sensor provided on the bottom surface of the passage 22 along with the photodiode 34, and the output of the magnetic sensor 44 is connected to the other terminal of the electronic switch 36 via the amplifier 45. The magnetic sensor 44, the photodiode 33, and the photodiode 34 form a sensor unit 46. In addition, the control unit 30, the Fourier transformer 38, the comparator 39, the correction circuit 40, the memory 41, and the determination unit 42 are configured by a microcomputer as software.

  The operation of the banknote recognition apparatus configured as described above will be described below.

  When the entrance sensor 32 detects the banknote 5, this detection signal is sent to the control unit 30. The control unit 30 rotates the motor 28 by operating the drive circuit 29 with this detection signal. As a result, the pulley 24 connected to the motor 28 rotates, and the transport belt 25 transports the banknote 5 toward the sensor unit 46. In addition, the conveyance amount of the banknote 5 at this time is detected by the synchronous pulse generator 31 and transmitted to the control unit 30. That is, the transport amount of the banknote 5 is measured by measuring the number of pulses output from the synchronous pulse generator 31 by the control unit 30.

  Accordingly, by driving the motor 28 by the drive circuit 29 while monitoring the signal output from the synchronization pulse generator 31, the specific position of the banknote 5 shown in FIG. Further, the bill 5 is normalized based on the output of the synchronization pulse generator 31. That is, since the conveyance speed of the banknote 5 by the drive circuit 29 is normalized, an error due to the conveyance speed can be reduced.

  When the bill 5 reaches the sensor unit 46, the light from the light emitting diode 33 passes through the bill 5 and is input to the photodiode 34. In this way, a signal that changes according to the pattern of the bill 5 is input to the photodiode 34. This signal is amplified by the amplifier 35. A signal that changes in accordance with the magnetism of the bill 5 is amplified by the amplifier 45 from the magnetic sensor 44. The signal from the photodiode 34 output from the amplifier 35 and the signal from the magnetic sensor 43 output from the amplifier 45 are appropriately selected by the electronic switch 36 and output to the next A / D converter 37. . Then, this A / D converter 37 converts it into a digital quantity. The signal converted into the digital quantity is subjected to Fourier series expansion by the next Fourier transformer 38 and converted into frequency information. That is, an arbitrary function f (x) can be expressed in the form of a sum of trigonometric functions by expanding the Fourier series as shown in (Equation 1). That is, amplitude information on the time axis can be converted into amplitude information on the frequency axis.

  FIG. 3 shows magnetic information at a specific position of the bill 5. In FIG. 3, the horizontal axis 51 is time, and the vertical axis 52 is amplitude. FIG. 4 shows the result of Fourier series expansion of the character information 53 in FIG. 3 by the Fourier transformer 38. In FIG. 4, the horizontal axis 54 is frequency and the vertical axis 55 is amplitude. Reference numeral 56 denotes a Fourier series expansion characteristic of the character information 53. By performing Fourier series expansion in this way, the time axis is converted to the frequency axis.

  FIG. 5 is a characteristic diagram of the characteristic 57 (shown by a dotted line) of the genuine note 70 and the characteristic 58 (shown by a solid line) of the counterfeit note 71 at a specific position of the banknote 5. In FIG. 5, the horizontal axis 59 is frequency and the vertical axis 60 is amplitude. By using 61, 62, and 63 where the difference between the characteristic 57 and the characteristic 58 is large, the genuine note 70 and the counterfeit note 71 can be discriminated.

  FIG. 6 is a characteristic diagram showing the difference between the average value 73 of the genuine note 70 and the counterfeit note 71. In FIG. 6, the horizontal axis 74 is frequency and the vertical axis 75 is amplitude. This is a relatively light portion of the banknote 5 and well represents the characteristics of the counterfeit note 71. That is, since the genuine note 70 is engraving intaglio printing, but uses a printer (inkjet color printer, laser printer, etc.) that forms a false ticket 71, the dot feature 76 is from 250 Hz to 350 Hz. Appear in. Therefore, by detecting this feature 76, the genuine note 70 and the counterfeit note 71 can be clearly distinguished. In the present embodiment, the feature appears up to about 350 Hz, but this comes from the restriction of the sensor unit 46 including the light emitting diode 33, and in fact, the feature of the dot appears up to about 1 KHz. it is conceivable that.

  FIG. 7 is a characteristic diagram in which the characteristics of the character portions of the genuine note 70 and the counterfeit note 71 are normalized at 100 Hz. In FIG. 7, the horizontal axis 81 is frequency, and the vertical axis 82 is amplitude. This is a characteristic comparison of the character portion of the banknote 5. 83 is a characteristic of the genuine note 70, and 84 is a characteristic of the counterfeit note 71. Thus, in the character portion, the features of the genuine note 70 and the counterfeit note 71 appear at 150 Hz or higher. The reason for selecting the normalization frequency as 100 Hz is that the frequency around this point is stable and that the difference due to the denomination information is difficult to enter.

  Moreover, about the discrimination | determination of the money type of the banknote 5, based on the Fourier series expansion | deployment of the specific position which shows the money type etc. of the banknote 5, the money type is discriminate | determined from the difference in the waveform.

  In this way, the change in amplitude on the frequency axis is compared with the value of the memory 41 in which the reference value is stored by the comparator 39. Then, the authenticator 70, the counterfeit note 71, and the denomination are determined by the determiner 42 based on the comparison amount. Then, the output is output from the output terminal 43. Note that the Fourier-transformed signal at this time is normalized by the conveyance speed of the banknote 5 output from the synchronization pulse generator 31. Therefore, the difference due to the banknote conveyance speed is corrected.

  Since the banknote discriminating apparatus according to the present invention has a stable discrimination capability, it can be applied to various automatic service devices such as vending machines and ticket vending machines.

The block diagram of the bill identification device in one embodiment of the present invention. Top view of banknote The time characteristic waveform figure of the characteristic part of the bill in one embodiment of the present invention Same as above, frequency characteristics waveform diagram of banknote features The first characteristic diagram that distinguishes genuine and counterfeit bills Same as above, second characteristic diagram for distinguishing genuine and counterfeit bills Same as above, the third characteristic chart that distinguishes genuine and counterfeit Block diagram of a conventional banknote recognition device

Explanation of symbols

5 bill 21 insertion slot 22 passage 23 pulley 24 pulley 25 transport belt 26 roller 27 roller 33 light emitting diode 34 photodiode 35 amplifier 37 A / D converter 38 Fourier transformer 39 comparator 41 memory 42 determination unit 44 magnetic sensor 45 amplifier 46 Sensor part

Claims (12)

A bill insertion port, a passage connected to the insertion port, a transport means for transporting a bill inserted in the passage, a sensor provided on the wall surface of the passage, and a sensor connected to the sensor An amplifier, an A / D converter connected to the output of the amplifier, a frequency analyzer connected to the output of the A / D converter, and an output of the frequency analyzer connected to one input A comparator connected to a memory storing a reference value at the other input, and a determiner connected to the output of the comparator, and an output from the A / D converter in the frequency analyzer A bill discriminating apparatus that Fourier-transforms a signal and discriminates the authenticity of a bill based on the Fourier transform waveform. The banknote identification device according to claim 1, wherein engraving intaglio printing and dot printing are distinguished by a Fourier transform waveform. The banknote identification device according to claim 2, wherein in a Fourier transform waveform, the authenticity of a banknote inserted with a waveform characteristic of 250 Hz to 1 KHz is determined. The banknote identification device according to claim 2, wherein the denomination of the banknote is determined based on a Fourier transform waveform at a specific position of the banknote. The banknote identification apparatus of Claim 1 which normalizes a Fourier-transform waveform with the passage time of a banknote. The banknote identification device according to claim 1, wherein the reference value is corrected by the output of the frequency analyzer. The bill identifying apparatus according to claim 1, wherein an optical sensor and a magnetic sensor are used as sensors, and a bill inserted is discriminated based on a signal output from the optical sensor and the magnetic sensor. The banknote according to claim 1, wherein the sensor provided on the wall surface of the passage includes a light emitting diode and a photodiode for receiving a light emission output from the light emitting diode, and the light emitting diode is formed of only one color light emitting diode. Identification device. The banknote identification device according to claim 1, wherein the sensor provided on the wall surface of the passage includes a light emitting diode and a photodiode that receives a light emission output from the light emitting diode, and the light emitting diode is formed of a red light emitting diode. The sensor provided on the wall surface of the passage includes a light emitting diode and a photodiode that receives a light emission output from the light emitting diode, and the light emitting diode is formed of a red light emitting diode including infrared light. Banknote identification device. The banknote identification according to claim 1, wherein the sensor provided on the wall surface of the passage comprises a light emitting diode and a photodiode for receiving a light output from the light emitting diode, and the light emitting diode is formed of an infrared light emitting diode. apparatus. The banknote identification device according to claim 1, wherein the sensor provided on the wall surface of the passage includes a light emitting diode and a photodiode that receives light output from the light emitting diode, and the light emitting diode is formed of a blue light emitting diode.

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