TW201717166A - Multi-frequency signal coin identification circuit - Google Patents

Abstract

A coin identification method that uses a multi-frequency ac voltage as the primary input voltage is proposed here. Two windings are used. A fixed amplitude, square-wave voltage is inputted to the primary winding to generate an AC flux linkages. Then, the second winding is used to detect the induced ac voltage. In addition, the induced voltage of the secondary winding is varied as a coin passes through the air gap. After that, by using Fourier analysis, the proposed system can determine the coin as a "real" coin or "fake" coin based on the different characteristics of the coin. The proposed system includes several advantages. It provides reliable output signal, simple hardware, and flexible characteristic.

Description

Multi-frequency signal coin recognition circuit

The present invention relates to a coin identifying device; and more particularly to a method for coin identification using a multi-frequency AC voltage oscillating coil.

Due to the high profitability of making counterfeit coins, many counterfeit coins similar in appearance, material, color and so on are successively appeared. Coin coin acceptors with poor recognition function often cannot distinguish the authenticity of coins, resulting in the use of automatic coin charging mechanism manufacturers. Loss. In view of this, in addition to the function of currency value recognition, coin coin acceptors must strengthen the ability to identify authentic and counterfeit coins, and domestic and foreign manufacturers have also launched such related products.

A coin-operated mechanism is used to carry coins, and an electromagnetic sensor composed of an oscillating coil and an induction coil is disposed at both ends of the coin transport path to recognize the coin type and authenticity of the coin, as shown in FIG. 1 is a patent document CN102209978B.

In FIG. 1, the primary side excitation signal is a rectangular wave of an arbitrary frequency output by a pulse width modulator 1a through pulse width modulation, and a corresponding composite signal 1b is generated, and a composite signal 2 composed of three frequencies is generated. After the driver 1c increases the ability to drive the coil, the primary side oscillation coil 1d is input.

Next, the receiving coil 1e amplifies the sensed signal through the amplifier 1f, inputs it to the AD converter 1g, and then stores the converted composite signal in the memory 1h for fast Fourier. The leaf converts 1i (FFT) and expands the respective frequency signals 3a, 3b, 3c of the composite signal onto the spectrogram 3.

If the above technique is used, if the primary side excitation signal needs to change the synthesis frequency, the corresponding filter 1b must be changed with the design, and the signal sensed by the secondary side receiving coil 1e must be amplified by the amplifier 1f before the signal can be made. Subsequent processing, again, as shown in Fig. 2, this patent document uses four electromagnetic sensor coils to achieve the described function, and the circuit scale is quite large.

In view of the above problems, an object of the present invention is to solve the problems of the prior art, and to provide a coin identifying apparatus and a coin identifying method capable of performing coin identification processing quickly and with high precision by a more compact circuit.

The first aspect of the present invention provides a more compact multi-frequency signal coin identification circuit, the coin identification circuit comprising: a driver for outputting a rectangular wave of arbitrary frequency through pulse width modulation by a pulse width modulator. There is no need to set a filter. After the drive increases the ability to drive the coil, it directly inputs the oscillating coil.

A voltage is applied to the composite signal induced by the secondary side receiving coil, and there is a problem of load effect, and the effect of the voltage passing through the clamp eliminates the load effect.

A subtractor, the digital signal processor can not accept the negative voltage, so the input voltage signal must first pass the subtractor to compensate the voltage signal to above zero.

A digital signal processor, after the composite signal induced by the receiving coil passes through the voltage follower and the subtractor, is input to the digital signal processor for Fourier analysis, and can obtain the voltage peak at any frequency.

A second aspect of the present invention provides a coin identification method for distinguishing The coin type and the authenticity of the coin include the following steps: the primary side excitation signal is a rectangular wave of arbitrary frequency output by pulse width modulation by a pulse width modulator, and the square wave signal does not need a filter circuit. After increasing the ability to drive the coil via the driver circuit, the primary side oscillating coil is input.

The synthesized signal induced by the secondary side receiving coil passes through the voltage follower and the subtractor, and is input into the digital signal processor for Fourier analysis, and the voltage peak at any frequency is obtained by the software, and the specific frequency voltage peak drawn is obtained. Adding the standardization reduces the error and builds a coin identification database.

32‧‧‧ drive

33‧‧‧Oscillation coil

34‧‧‧ receiving coil

35‧‧‧Voltage follower

36‧‧‧Subtractor

37‧‧‧Digital Signal Processor

Figure 1 is a block diagram of the patent document CN102209978B.

2 is a statistical diagram of a coil used in accordance with Patent Document 102209978B.

Figure 3 is a block diagram of a multi-frequency signal coin identification circuit of the present invention.

4 is a flow chart of a method for identifying a multi-frequency signal coin of the present invention.

Figure 5 is a waveform diagram of the measured four coins of the present invention.

Fig. 6 is a bar graph of four harmonic peaks obtained by Fourier analysis of the four coin synthesis signals of the present invention.

Fig. 7A is a line diagram of the same coin value (50 yuan) of the present invention but different coins.

Fig. 7B is a line diagram of the same currency of the present invention (50 yuan) but different coins are added to the standard.

The present invention will be further understood by those skilled in the art to which the present invention pertains, and the present invention will be described in detail below with reference to the accompanying drawings. The content of the Ming and the effect it wants to achieve.

3 is a block diagram of a multi-frequency signal coin identification circuit of the present invention. In FIG. 2, the multi-frequency signal coin identification circuit includes a driver 32, an oscillating coil 33, a receiving coil 34, a voltage snubber 35, and a A subtractor 36 and a digital signal processor 37.

In the present embodiment, the excitation signal applied by the oscillating coil 33 is a rectangular wave of arbitrary frequency outputted by the pulse width modulator through pulse width modulation, and does not need to be filtered by the filter 1b into a composite signal composed of a specific frequency, and is directly excited. Rectangular wave, because in the concept of Fourier analysis, the rectangular wave can be equivalent to a composite waveform composed of many sine waves of different frequencies, which can save the process and hardware cost of the specially designed filter 1b circuit.

Further, in the selection of the coil, the primary side oscillation coil 33 and the secondary side receiving coil 34 are not two identical coils, and the secondary side receiving coil 34 is provided with a coil slightly larger than the primary side oscillation coil 33. The purpose is to achieve the effect of magnetic flux amplification for the primary side and the secondary measuring coil, thereby amplifying the combined signal sensed by the secondary side receiving coil 34 without externally applying the amplifier 1f circuit, and the aforementioned Chinese patent 102209978B This saves the hardware cost of the amplifier 1f and makes the circuit more streamlined.

Referring again to FIG. 3, the composite signal induced by the receiving coil 34 is subjected to voltage cancellation by the voltage counter 35 and the subtractor 36 compensates the voltage to above zero, and is input to the digital signal processor 37, which is used for digital signal processing in this embodiment. Device 37 is a TMS320F2808 produced by Texas Instruments. It can be used with the light-blocking device attached to the coin-operated mechanism to judge whether the coin is put into the coin-operating mechanism and judge the size of the coin. These functions can be achieved without adding any software. The hardware circuit simplifies the scale of the coin identification circuit.

As shown in FIG. 4, this is the flow of the method for identifying the multi-frequency signal coin of the present embodiment. In the figure, the photointerrupter attached by the coin-operating mechanism is used as a basis for judging whether or not the coin is put in. When the coin is put into the trigger photointerrupter S41, then the secondary side receiving coil 34 is waited for the composite signal to be sensed, and the secondary side receives the coin. The composite signal sensed by the coil and the rectangular wave excited by the primary side oscillation coil are completely in the same direction, so the excitation signal is used as one of the trigger conditions for triggering the AD converter to start the conversion, when the photointerrupter S41 and When the excitation signal S42 is simultaneously triggered, the AD converter starts to convert the synthesized signal induced by the secondary side receiving coil of S43, converts the analog signal into a digital signal, inputs the digital signal processor, performs Fourier analysis, and uses the software to extract the synthesized signal. The voltage peak S44 of any frequency can be arbitrarily selected to establish a coin identification database S45 by using voltage peaks of several different frequencies. In this embodiment, voltage peaks of three different frequencies are used to identify the currency type of the coin, and the judgment is true coin S46. Still fake currency S47.

After the multi-frequency signal coin identification circuit and method are set according to the above implementation method, the coin identification database S45 can be established. In this embodiment, the four common coins of the Republic of China are established using the voltage peaks S44 of three different frequencies, respectively, 50 yuan, 10 yuan, 1 yuan and 5 yuan.

As shown in FIG. 5, the primary side oscillation coil 33 excites a rectangular wave, and measures the wave of the composite signal induced by the secondary side receiving coil 34 when the coinless, 50 yuan, 10 yuan, 1 yuan, and 5 yuan are input into the coin-operating mechanism, respectively. The pattern can be seen from the above five cases. The voltage peak of the composite signal changes quite clearly, and it can indeed distinguish four coins of different currency values.

Figure 6 is a bar graph of the voltage peaks of three different frequencies after Fourier analysis of the quadratic composite signals of the four coins of 50 yuan, 10 yuan, 1 yuan and 5 yuan, followed by the 3rd harmonic (6kHz) ), 5th harmonic (10kHz) and 9th harmonic (18kHz). Through the comparison of the bar graphs, it can be seen that the difference in voltage peak values of the four different coins is very obvious. This embodiment takes three different Frequency peak voltage to establish a coin identification database of 4 kinds of coins, which can be accurately judged The currency type and authenticity of the four coins.

As shown in FIG. 7A, it can be found that in the case of the same currency value (50 yuan), if different coins are input, an error value exists, and the multi-frequency signal coin identification method proposed by the present invention is to make the coin identification database. More accurate in identifying coins, in the embodiment, the voltage peaks of the three different frequencies captured are proportional to each other, that is, the 3rd harmonic is divided by the 5th harmonic, and the 3rd harmonic is divided by the 9th harmonic. Wave, 5th harmonic divided by 9th harmonic, can be obtained in Figure 7B. It can be seen from the comparison of Figure 7A and Figure 7B that in the case of the same currency value (50 yuan), different coins are put into this embodiment. The error value between the coins is significantly reduced, and the accuracy is relatively improved for the resolution of the coin type and the identification of the authenticity. In other embodiments, the application of the proportional relationship is slightly modified, and the The voltage peaks of the three different frequencies are proportional to the fundamental frequency voltage peak, that is, the third harmonic (6 kHz) divided by the fundamental frequency wave (2 kHz), the fifth harmonic (15 kHz) divided by the fundamental frequency wave (2 kHz), The 9th harmonic is divided by the fundamental frequency wave (2kHz), which is similar to the application method of the standardization. Error value between coins significantly reduced, greatly enhance the coin denomination and authenticity of the identification accuracy of the method used in the present invention.

The invention provides a multi-frequency signal coin identification circuit and a method, the advantages of which provide a relatively simple coin identification circuit, that is, the primary side rectangular wave excitation signal does not need to pass through a specially designed filter 1b circuit, and the secondary side receiving coil senses The synthesized signal is designed to have a magnetic flux amplification effect due to the design of the primary side and the secondary side turns ratio, so that the synthesized signal induced by the secondary side does not need to pass through the amplifier 1f circuit, and can be input to the digital signal processor 37 for subsequent operation. The Fourier analysis process can greatly reduce the scale and cost of the hardware circuit. In addition, in addition to freely extracting the voltage peak of any frequency in the synthesized signal, it also adds a standardization to reduce the error value and make the coin identification established. The accuracy of the database has increased dramatically.

The present invention has been described above with reference to the preferred embodiments and the accompanying drawings, and should not be considered as limiting. Various modifications, omissions and changes may be made without departing from the scope of the invention.

31‧‧‧ Pulse width modulator

32‧‧‧Drive circuit

33‧‧‧Oscillation coil

34‧‧‧ receiving coil

35‧‧‧Voltage follower

36‧‧‧Subtractor

37‧‧‧Digital Signal Processor

Claims (4)

A multi-frequency signal coin identification circuit provides a more compact multi-frequency signal coin identification circuit, the coin identification circuit comprising: a driver for outputting a rectangular wave of arbitrary frequency through a pulse width modulation by a pulse width modulator, without The filter circuit is set, and after the driver increases the ability to drive the coil, the oscillation coil is directly input. A voltage is applied to the composite signal induced by the secondary side receiving coil, and there is a problem of load effect, and the effect of the voltage passing through the clamp eliminates the load effect. A subtractor, the digital signal processor can not accept the negative voltage, so the input voltage signal must first pass the subtractor to compensate the voltage signal to above zero. A digital signal processor, after the composite signal induced by the receiving coil passes through the voltage follower and the subtractor, is input into the digital signal processor for Fourier analysis, and can obtain the voltage peak at any frequency. The coin identification circuit of claim 1, wherein the digital signal processor comprises: a pulse width modulator capable of outputting a rectangular wave of an arbitrary frequency for exciting the oscillation coil as a multi-frequency signal and As one of the trigger conditions for the AD converter to start converting the secondary side composite signal. An AD converter, when the coin is put into the coin-operated device, triggers the photointerrupter signal. In this case, if the rectangular wave outputted by the pulse width modulator starts to excite the oscillation coil once, both conditions are simultaneously established. The AD converter will start to convert the composite signal induced by the secondary side receiving coil, and after converting the analog signal into a digital signal, perform Fourier analysis to obtain a voltage peak at an arbitrary frequency. A multi-frequency signal coin identification method for identifying a coin type and authenticity, the coin identification method comprising the following steps: the primary side excitation signal is a rectangular wave of arbitrary frequency output by a pulse width modulation device through pulse width modulation. This square wave signal does not require a filter circuit, and after adding the ability to drive the coil via the driver circuit, the primary side oscillation coil is input. The synthesized signal induced by the secondary side receiving coil passes through the voltage follower and the subtractor, and is input into the digital signal processor for Fourier analysis, and the voltage peak at any frequency is obtained by the software, and the specific frequency voltage peak drawn is obtained. Adding the standardization reduces the error and builds a coin identification database. The coin identification method of claim 3, wherein the primary side oscillating coil and the secondary side receiving coil are not two identical coils, and the secondary side receiving coil is set to be slightly larger than the primary side oscillating coil turns ratio The purpose of the coil is to achieve the effect of magnetic flux amplification on the primary side and the secondary measuring coil, thereby amplifying the composite signal induced by the secondary side receiving coil without using an external amplifier circuit, and the aforementioned Chinese patent 102209978B This saves the hardware cost of the amplifier and makes the circuit more streamlined.