Abstract:
A coin discriminator comprises photoreceivers along a vertical drawn from an infed coin run chute whereby screening and illuminating the photoreceivers from a photoemissive source permit coin diameter identification. Two coils on either side of the chute detect the coin alloy. Coin thickness is determined using a stepshaped transversal section across the chute track where the step risers lie opposite the photoreceivers which transmit a signal word identifying the infed coin diameter and thickness. This signal word is compared with memorized words representative of acceptable coin dimensions. If the dimensions are acceptable, a combination of impedances in a bridge circuit incorporating the coils is selected in terms of the alloy corresponding to the acceptable dimensions. If the bridge balances for this combination as the coin rolls between the coils, the coin is accepted.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a multicoin (multitoken) discriminator comprising a chute having a vertically inclined track on which infed coins (tokens) roll. The coin discriminator is intended for an automatic object or service vending machine. 
     2. Description of the Prior Art 
     Multicoin discriminators as described in French patent applications 2,461,987 and 2,466,055 comprise coin dimension recognizing means in the form of two electromagnetic field producing coils on either side of the coin roll-in chute. The diameters of the coils are such that the upper tip of a coin having a minimum acceptable diameter enters only a small portion of the coil electromagnetic field; a coin having the maximum acceptable diameter enters the entire electromagnetic field. One of the coils, referred to as an oscillating coil, is connected to an oscillating circuit which delivers a high frequency signal, typically 100 kHz. The other coil, a so-called receiving coil, transmits a voltage to voltage comparison means; the voltage is proportional to the magnetic flux intensity through which the upper part of each coin passes. Reference voltages representative of the diameters of varying acceptable coin types are compared with the voltage transmitted by the receiving coil to deduce whether the coin should be accepted; if the coin is acceptable it has a diameter between the minimum and maximum diameters; otherwise the coin is refused. 
     In the foregoing patent applications, the coin alloy detecting means make use of the same voltage comparison principle. 
     Another coin discriminator, disclosed in French patent application 2,448,752, selects only one type of coin, i.e., admits only coins having a predetermined diameter and made of a predetermined alloy or material. 
     The principle behind the means for recognizing alloys resides in the description hereinabove. The alloy recognizing means also comprises two coils disposed opposite each other. One of the coils is excited by an a.c. generator. A signal induced in the other coil has an amplitude that is compared with a predetermined voltage to determine if the coin between the coils is acceptable; if the amplitude is less than the predetermined voltage the coin is acceptable. 
     The coin dimension recognizing means taught in French patent application 2,448,752 comprises two light sources and phototransistor light detecting pairs. The light detectors are spaced from each other by a distance virtually equal to the acceptable coin type diameter. Should one or both the phototransistors be excited, the infed coin does not have the required diameter and is rejected. 
     Known previous discriminators thus adopt coin diameter and alloy as the sole selection criteria. An infed coin having the acceptable diameter and alloy is therefore accepted regardless of thickness. This offers a further non-negligible opportunity of fraudulently introducing improper coins or slugs into the vending machine. Moreover, the diameter recognizing means taught in French patent application 2,466,055 permits acceptance of coins having diameters that vary over only a relatively small range. If the vending machine is to accept coins having many different diameters, the measurement device for distinguishing between the diameters require high sensitivity and very precise setting; the number of voltage comparing circuits equals the number of different diameters. The alloy recognizing means also requires a number of voltage comparing circuits equal to the number of denominations to be detected. 
     OBJECTS OF THE INVENTION 
     The main object of this invention is to provide a multicoin discriminator which discriminates infed coins in terms of the coin thickness. 
     Another object of this invention is to provide a multicoin discriminator which discriminates the infed coins in terms of the coin diameter, thickness and alloy. 
     A further object of this invention is to provide a multicoin discriminator in which the dimension recognizing means and the alloy recognizing means are unique and utilized for all coin types. 
     SUMMARY OF THE INVENTION 
     To discriminate coins in terms of diameter and thickness, a multicoin discriminator in accordance with one embodiment of the invention, comprises photoemission means lodged in one of the side walls of the coin chute for selectively illuminating photoreceptive means lodged on the other side wall of the chute and in front of the photoemissive means for detecting the dimensions of the infed coins. A stair-shaped transversal cross-section between the photoemissive means and photoreceptive means positioned in the bottom of the chute has its lowest step or platform adjacent an inclined side wall of the chute against which one face of the coins rests. 
     The photoreceptive means can comprise several charge transfer devices (CTD) or several phototransistors aligned respectively opposite to risers of the stair-shaped transversal cross-section and likely to capture the preferable infrared rays emitted by the photoemissive means. 
     The stair cross-section in the track provides thickness differentiation regarding the acceptable coins. By screening the photosensitive receivers opposite the risers and other photosensitive receivers above the step, a binary word is produced which identifies the diameter thickness of each acceptable type of coin. Recognition of acceptable dimensions is achieved by means connected to the photosensitive receivers for detecting a diameter and thickness identification word for each coin fed into the chute, a memory having memorized words respectively identifying the acceptable coin dimensions and means for comparing each detected word with the memorized words in order to accept or reject the infed coin. 
     According to another aspect of the invention, the stepshaped transversal cross-section is replaced by an inclined plane cross-section making a predetermined acute angle with the inclined side wall of the chute. 
     To discriminate coins in terms of alloy, a multicoin discriminator comprises two series-connected coils on opposite sides of said chute for detecting the alloy of each infed coin, oscillator means having a predetermined-frequency, and means for memorizing words representating the alloys of acceptable coins. Two combinations of parallel impedances are respectively addressable by all said memorized words for each infed coin. An impedance bridge means excited by said oscillator means has four arms, one of which includes the two series-connected coils. Two adjacent arms respectively include the two parallel impedance combinations. A bridge means balance detection means compares the detected alloy of each infed coin with all said alloys representated by said memorized words to accept or reject said infed coin. 
     According to other aspects of the invention, a complete multicoin discriminator embodying the invention comprises the above diameter and thickness discriminating means and the above alloy discriminating means. One of these two discriminating means can accept an infed coin after the other has detected and validated the infed coin in terms of the diameter and thickness, and the alloy. 
     Other features, advantages and objects of this invention will be more clearly apparent from the following description of preferred exemplified embodiments as illustrated in the accompanying corresponding drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic longitudinal cross-section view along the coin chute of the position of the various means incorporated in a multicoin discriminator embodying the invention; 
     FIG. 2 is a side view of the chute having a step-shaped transversal cross-section; 
     FIG. 3 is a plan view of the chute track of FIG. 2; 
     FIG. 4 is a cross-sectional view along the line IV--IV in FIGS. 2 and 3; 
     FIGS. 4A and 4B are cross-sectional views of a coin chute track having an inclined plane cross-section; 
     FIG. 5 is a cross view analogous to FIG. 4 of thin and thick coin runs; 
     FIG. 6 is a schematic side view of the chute of FIG. 2 showing the positioning of the photosensitive receivers with regard to the risers of the step cross-section; 
     FIGS. 7, 8 and 9 are cross-sectional views analogous to FIG. 4 depicting the runs of two coins having different diameters and thickness and of a washer on a step; 
     FIG. 10 is a block diagram of a dimension comparing circuit; 
     FIG. 11 is a block diagram of the alloy comparing circuit; and 
     FIG. 12 is a block diagram of the dimension comparing circuit structured around a microprocessor according to another embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Schematically depicted in FIG. 1 is a discriminator for coins or tokens presenting different diameters, thickness and alloys. The discriminator includes coin C dimension recognizing means 1--2 and coin C alloy recognizng means 3--4. Each of these means comprises a coin detecting device 1, 3 that is located along chute 5 for the coin C gravity infed run and a circuit 2, 4 associated with respective detecting device 1, 3 for comparing the detected dimensions or alloy with the pre-recorded values therefor. Circuits 2 and 4 are included in a logic control unit 6 which, from the comparison results, determines whether an infed coin is to be accepted and honored or rejected and reimbursed. 
     The multicoin discriminator is located in a known object or service vending machine. Mention is made henceforth solely of those means in this machine directly related to the multicoin discriminator. 
     As shown in FIG. 1, run chute 5 has an input 50 having a single slot into which the coins are fed, and a double output 51--52. The double output consists of a first output 51 for acceptable coins that fall into a collection box in the vending machine and a second output 52 for the rejected coins above the vending machine reimbursement receptacle. The chute output selection between the accepted and rejected coins is obtained by means of an electromagnet 60 that is controlled by unit 6 through a wire 61. Electromagnet 60 holds the bottom of the run chute open by means of a retractable hatch 62 until such time as the relative dimension or alloy comparisons are no longer negative. 
     Run chute 5 generally has a rectangular cross-section and descends along a track 53 from input 50 down to output 51--52. In the illustrated embodiment, starting from input 50, a coin first crosses dimension detecting device 1 and then crosses alloy detecting device 3. 
     In reference now to FIGS. 2 and 4, the width of chute track 53 is equal to the largest acceptable coin thickness. Track plane 53e at the input 50 end is a higher level than plane 53a of the track running from device 3 down to output 51--52. Between parallel planes 53e and 53a that have the same direction if inclination, the track is formed as a staircase having plural risers and platforms (steps) in cross-section at right angles to the rolling direction of coin C as illustrated in FIG. 4. The stepped section is illustrated as comprising three intermediate steps 54b, 54c, and 54d, located between lower step 54a and upper step 54e. Steps 54a and 54e are coplanar with the track planes 53a and 53e respectively. 
     Moreover, longitudinal side walls 550 and 551 of chute 5 are rearwardly inclined such that gravity causes all the coins to rest on lower wall 550. 
     As shown in FIG. 3, the longitudinal transitions or risers between plane 53e that is an extension of upper step 54e, and following step 54d, between steps 54d and 54c, between steps 54c and 54b and between step 54b and lower plane 53a that is an extension of step 54a, are respectively formed of rectangular inclined planes 56d, 56c, 56b and 56a. These inclined planes adjoin wall 550 against which one of the coin faces rests by gravity. Downstream of device 1 and upstream of device 3, the chute further comprises inclined planes 57d and 57a which form respective transitions between steps 54e to 54a; planes 57a-57d are adjacent upper longitudinal wall 551. As can be seen in FIG. 3, steps 54e to 53a between walls 551 and 550 form longitudinal parallel strips, each off-set with respect to the previous one down to the output. 
     The inclined planes provide a progressive descent for coins with differing thickness between upper plane 53e and lower plane 53a of the track. It goes without saying that other configurations and longitudinal lay-outs of the inclined planes may be envisioned. 
     Generally speaking, each stair in the staircase has a different height and width. 
     The distances between rear support wall 550 and the risers and other wall 551 are slightly greater than the five different acceptable coin thickness. For example, as depicted in FIG. 5, a thin coin C a  rolls from the upper track plane 53e successively over inclined planes 56d to 56a and along lower step 54a whereas a coin C e  having a thickness greater than the distance between wall 550 and the upper riser and equal at the most to the width of chute 5, runs firstly over upper step 54e and then over inclined planes 57d to 57a. 
     Semiconductor photosensitive receivers 10a to 10i respond to light energy from source 11, as blocked by token or coin C, as it rolls through device 1 to enable the coin thicknesses and diameters to be detected. The length of a region of receivers 10a to 10i that is not illuminated determines the token diameter. The length of a zone of receivers 10a to 10i between lowest step 54a and the lowest edge of token C that is illuminated indicates the coin thickness; the coin thickness is detected only while the coin diameter is detected. 
     With reference to FIGS. 2 to 6, dimension detecting device 1 comprises a photoemissive source 11 and a plurality of photosensitive receivers 10a to 10i such as phototransistors. Photoemissive source 11 may emit optical energy in the visible band, but preferably is an infrared emitter to obviate any parasitic detection of light that might stem from coin input slot 50. Photoemissive source 11 includes either a lamp or a light-emitting diode (LED) or several photoemissive diodes. The photosensitive receivers can be replaced by any other electro-optical means such as charge transfer device (CTD) or camera, e.g. a bar of charged coupled devices (CCD) described in detail hereinafter. Photoemissive source 11 is fixed behind a slit 12 in upper side wall 551 of the chute and is perpendicular to chute track 53 and thus to all steps 54e to 54a. Phototransistors 10a to 10i are inserted in support wall 550 where they are also aligned with the vertical from track 53 in the transversal plane that is perpendicular to walls 550 and 551 and median to slit 12. The transversal plane follows line IV--IV in FIGS. 2 and 3 and lies in line with a step transversal section of track 53. Slit 12 can be replaced by holes formed in chute upper wall 551. One hole is provided for each of transistors 10a to 10i, so each is aligned with the vertical from chute track 53 and positioned opposite the phototransistor associated with it. 
     As illustrated in FIG. 6, lower phototransistors 10a to 10d are respectively positioned opposite the centers of the straight risers. In the drawing, phototransistors 10e to 10i are equally spaced between upper step 54e and the upper edge of wall 550. However, in practice, the number of phototransistors 10a to 10i can be greater and the phototransistors can be spaced from each other by distances associated with the various acceptable coin diameters. Last phototransistor 10i is usually slightly higher than the highest acceptable coin rolling down the step section in order to detect any improper coins or slugs having an excessive diameter. 
     As a result, depending on phototransistor screening and excitation, circuit 2 in logic unit 6 can deduce the diameter and thickness of a coin. When photoemissive source 11 excites a lower phototransistor 10a to 10d, the thickness of the coin is greater than the distance between support wall 550 and the corresponding riser. Between the highest excited lower phototransistor 10a to 10d and the lowest excited phototransistor, the other phototransistors are screened to indicate the coin diameter. 
     Three examples of coins to be detected are given in FIGS. 7 to 9. The high logic signals a to i indicate the respective excitation of phototransistors 10a to 10i whilst complementary logic signals a to i indicate the respective screening of phototransistors 10a to 10i. 
     As seen in FIG. 7, the width of an infed coin C c  lies between the distances separating wall 550 from the risers of steps 54c and 54d. Coin C c  therefore rolls along step 54c. The diameter of coin C c  is slightly greater than the distance between phototransistors 10c and 10g. As a result, phototransistors 10c to 10g are screened and phototransistors 10a, 10b, 10h and 10i are excited by source 11. In this case, a bus 13 connected to the phototransistors delivers the detected word a b c d e f g h i to circuit 2. 
     Referring now to FIG. 8, the infed coin C b  rolling along second step 54b has a diameter slightly greater than the distance between phototransistors 10b and 10h. The word detected and delivered along bus 13 is a b c d e f g h i. 
     In FIG. 9, the coin W has the same dimensions as in FIG. 8, but has a hole drilled through the center thus forming a washer. The central hole of coin W enables radiation from source 11 to be incident on and excite phototransistor 10e, thus causing the word transmitted on bus 13 to be a b c d e f g h i. Consequently, when circuit 2 recognizes at least two separate signal groups at the lower level in the logic signal derived by detectors 10a-10i, it deduces that the infed coin has a hole through it; the coin is thus unacceptable and must be rejected by retracting hatch 62 controlled by eject electromagnet 60. 
     Should a buckled coin become jammed, means (not shown) can be provided for ejecting the coin manually or electromechanically into the reimbursement receptacle by off-setting at least chute support wall 550. 
     Each acceptable coin is characterized by a word identifying the coin diameter and the thickness. In the embodiment illustrated in FIG. 10, dimension comparing circuit 2 comprises a read-only memory (ROM) 20 having predetermined addresses containing nine-bit words respectively identifying the dimensions of all coin types the vending machine is supposed to accept. The memory 20 is preferably reprogrammable (REPROM) thus allowing the company managing the machine to select the acceptable coins in terms of the service or object vending cost. 
     Circuit 2 further comprises, in the embodiment illustrated, a buffer shift register 21 with at least nine stages, a time base 22, a read addressing circuit 23 for read-only memory 20 and a logic comparing circuit 24 having input buses 240, 241 connected to the parallel outputs of memory 20 and register 21. Bus 13 transmits the parallel bits of the dimension identifying binary words to time base 22. 
     Time base 22 periodically reads the words in bus 13 and includes means for successively comparing these words two by two in order to select and retain only that word having the greatest number of bits with the low logic level between two predetermined instants closely corresponding to a coin passing between slit 12 and phototransistors 10a to 10i. The selected word corresponds to the diametral section of the coin passing through the chute. Time base 22 then orders the following cycle. 
     The selected identification word is recorded in buffer register 21 via a bus 220. Next, via a lead 221, the time base simultaneously controls the reading of register 21 and the reading of a first acceptable coin dimension identifying word in memory 20 to addressing circuit 23. Comparing circuit 24 transmits the comparison result via output lead 242 thereof to time base 22. Until such time as the comparison result is no longer negative, the time base orders other acceptable coin identifying words memorized in read-only memory 20 to be read in order to compare them with the word detected and recorded in register 21. 
     Should no comparison be positive, time base 22 sends orders via wire 61 for the infed coin to be rejected by opening hatch 62. For a positive comparison, the memory 20 reading cycle is halted and an address is transmitted via bus 200 from memory 20 to an alloy memory 40 incorporated in alloy comparing circuit 4. Each coin dimension identifying word stored in memory 20 is stored with an address word from memory 40 which characterizes the alloy of that coin having acceptable dimensions corresponding to the identification word that is detected in the time base 22 and stored in the register 21 of circuit 2. 
     When the multicoin discriminator embodiment does not comprise device 3 and circuit 4, the address words for memory 40 go unused. 
     According to another embodiment illustrated in FIGS. 4A and 4B, the photoreceptive receiving means included in the dimension detecting device 1 includes a charge coupled device (CCD) bar. The N cells 14 1  to 14 N  of the CCD bar replace the phototransistors 10a to 10i. In practice, the integer N is higher than the number of phototransistors because of the integrated structure of the bar. The vertical definition with a CCD bar may reach at least a tenth of a millimeter. The CCD bar is lodged in the support side wall 550 and is perpendicular to the track 53 of the run chute 5 and opposite the slit 12. 
     As shown in FIGS. 4A and 4B, the steps 54a and 54d are replaced by an inclined plane 58 making a predetermined acute angle α with respect to the lower support wall 550. When an infed coin C rolls down chute 5, gravity causes one of its faces to rest against wall 550; the edge of its opposite face rolls on inclined plane 58 that is provided between upper track 53e and lower track 53a. As previously, the screened CCD cells, such as above cell 14 3  for a thin coin C f  having a thickness Δt f  (FIG. 4A), or above cell 14 5  for a thick coin C g  having a thickness Δt g  (FIG. 4B), give the diameter of the coin. The excited lower cells, such as cells 14 1  and 14 2  for coin C f  or cells 14 1  to 14 4  for coin C g , directly define the thickness Δt of the coin according to the formula: 
     
         Δt=Δl·t.sub.g α 
    
     where Δl is the distance between the lower portion of the coin and the apex of angle α, i.e. the length along which the lower cells are excited. Preferably, α is equal to π/4 to simplify the calculation since Δt=Δl for this case. 
     The dimension comparing circuit according to this embodiment enables the coin diameter to be determined, as above mentioned. The dimension comparing circuit further enables the coin thickness to be directly determined in terms of the formula Δt=Δl by comparing the word that is delivered from the lower excited CCD cells, with a memorized thickness identifying word for the corresponding diameter of an acceptable coin. 
     The multicoin discriminator according to this embodiment is suitable for all the acceptable coin types without mechanical modifications; on the contrary, the width of each step according to the first embodiment corresponds to a predetermined coin thickness. These modifications are only obtained by programming the acceptable coin thickness and diameter table that is stored in the reprogrammable memory (REPROM) in the circuit 2. 
     In reference now to FIG. 11, a description follows of alloy recognizing means 3-4. 
     Alloy detecting device 3 comprises, as is known, two electromagnetically coupled coaxial coils 30 and 31 opposite one another. Coils 30 and 31 are respectively inserted in longitudinal side walls 550 and 551 of run chute 5 above lower plane 53a. The common axis of coils 30 and 31 is perpendicular to walls 550 and 551 and preferably lies in line with the average center of the coins rolling along plane 53a, in line, for example, with that of upper step 54e. 
     Beside the already mentioned alloy identifying word memory 40, circuit 4 comprises a Wheatstone bridge circuit 41, an amplifying circuit 42, an integrating circuit 43 and a threshold comparing circuit 44. 
     Terminal 410, common to two adjacent arms in impedance bridge circuit 41, is connected via input resistor 421 to direct input 420 +   of an operational amplifier 420 that is included in amplifying circuit 42. Each of these two arms has a plurality of parallel-connected circuits 451-461 to 454-464, 455-465 to 458-468, numbering in this four, for instance. Each of these circuits comprises a complex impedance 451 to 458 (that may be adjustable) and an analog switching circuit 461 to 468 of the relay-controlled contact type, resistor type or the RCA CD4066 &#34;analog switch&#34; type for example. The first of the foregoing arms (the upper one in FIG. 11) comprises, in series with four parallel-connected circuits 451-461 to 454-464, two series-connected coils 30 and 31 together with a complex impedance 411 that may include a thermistor. The second foregoing arm (the lower one in FIG. 11) comprises two impedances 413 and 414 that are respectively and preferably resistive and capacitive and are connected in series with the other four parallel-connected circuits 455-465 to 458-468. 
     Applied to the other terminals 415-416 of the foregoing arms of bridge circuit 41 is the voltage from a.c. generator 417 having a predetermined-frequency suitable for discriminating between coin alloys. Between terminals 415 and 416 are the third and fourth arms Wheatstone bridge circuit 41, respectively comprising impedances 418 and 419, that are preferably resistive and capacitive and are connected to ground. 
     In analog amplifying circuit 42, inverse input terminal 420 -   of amplifier 420 is connected to grounded resistor 422, and a feedback resistor 423 that is connected to output 424 of amplifier 420. 
     Integrated circuit 43 comprises two resistors 430 and 431 having a common terminal connected to a grounded capacitor 432. The other terminal of resistor 431 is connected to one of inputs of the voltage comparator 411 which is included in circuit 44. 
     Threshold comparing circuit 44, between the positive supply terminal and ground, further includes a resistor 442 and a potentiometer 443, having a common terminal connected to a resistor 444. The other terminal of resistor 444 is connected to a common terminal of grounded capacitor 445 and input 446 of comparator 441. The output of comparator 441 is connected via controlling wire 61 to electromagnet 60 for ejecting refused coins. Potentiometer 443 is set such that the voltage across comparator terminal 446 is equal to the bridge circuit 41 balance voltage applied to terminal 440 via circuits 42 and 43. 
     Each group of analog switches 461 to 464, 465 to 468 is controlled by a 4-lead output bus 401, 402 from alloy identifying word memory 40. Prior to any utilization of the device, adjustable impedances 451 to 458 are set such that for certain open and closed combinations of switches 461 to 468, i.e. predetermined impedance 451 to 458 combinations, each of the alloys or materials characterizing all the acceptable coins introduced between coils 30 and 31 indicates the bridge circuit balance status; the bridge balance status is indicated by a high logic level output signal on wire 61. An alloy identifying word in reprogrammable read-only memory 40 (REPROM) corresponds to each switch open/close or impedance combination for each predetermined alloy. 
     Subsequent to time base 22 (FIG. 10) enabling the diameter and thickness dimension for an infed coin in response to recognition of a dimension identifying word transmitted along bus 13 and stored in memory 20, memory 20 delivers to bus 200 the alloy identifying word address that is memorized in the memory 40 and which corresponds to the alloy of an acceptable coin with the detected dimensions; bus 200 is supplied with the alloy word after a lapse of time corresponding to the time the coin takes to run between devices 1 and 3. Switches 461 to 468 are controlled via buses 401 and 402 and positioned to enable the corresponding alloy to be detected. If the infed coin causes bridge circuit 41 to be balanced upon running between coils 30 and 31, comparator 441 activates ejection electromagnet 60 (FIG. 1) to close hatch 62 over which the coin rolls towards the output 51 and the collection box. In the opposite case, if the coin has the appropriate dimensions, but bridge 41 is not balanced since the coin composition does not correspond to the required alloy for such dimensions, the low level signal on wire 61 holds hatch 62 open and the coin is returned to the user. 
     In the embodiment wherein the multicoin discriminator comprises only means for recognizing alloys 3-4, circuit 4 fulfills functions analogous to circuit 2. In this case, circuit 4 comprises a time base 22 which successively readouts addresses of the alloy identifying words in memory 40 until the time base detects a low level signal at the output of comparator 441; the low level output enables the infed coin. Alternatively, if the output of comparator 441 indicates no balance of bridge circuit 41 for all the close/open combinations of analog switches 461 to 468 stored in memory 40, hatch 62 stays open to reject the unacceptable coin. 
     In a further embodiment, alloy detecting device 3 can be located upstream of dimension detecting device 1 along the chute 5 coin track. In this case, the relative control functions of circuits 2 and 4 are reversed. Circuit 4 comprises a time base 22 which cyclically reads memory 40 until bridge circuit 41 is detected as balanced. In response to this balance, memory 40 addresses memory 20 so comparator 24 can compare the word on bus 13 with that addressed in memory 20. As previously, if the bridge circuit is balanced and if, for this balance, the comparison result in comparator 24 is positive, hatch 62 is activated to close the chute track. 
     Lastly, in a more integrated embodiment, dimension recognizing circuit 2 is structured around a microprocessor 25, as shown in FIG. 12. The microprocessor 25 comprises a random access memory (RAM) that is utilized for successive two-by-two comparisons of the words coupled to bus 13 as the coin rolls through the chute. Circuit 2 further comprises a reprogrammable memory 26 and an input/output interface 27. Pre-recorded in memory 26 are the acceptable coin dimension identifying words and the orders corresponding to the comparison cycle, as described herein with reference to FIG. 10. Circuits 25, 26 and 27 are interconnected conventionally via a unidirectional bus 28 for the addresses leaving microprocessor 25 and via a bidirectional bus 29 for the orders and data. Interface 27 is linked to bus 13, connected to photoemissive means 10a to 10i (FIG. 5) or 14 1  to 14 N  (FIGS. 4A and 4B); bus 200, serving alloy identifying word memory 40 (FIG. 11), controls wire 61 of electromagnet 60 that controls retractable hatch 62 (FIG. 1), and directly, in this case, to respond to the output of voltage comparator 44 (FIG. 11). Bus 270 can connect interface 27 to other equipment, such as a display means. In this microprocessor embodiment, memory 40 (FIG. 11) can also take the form of a microprocessor.