US3152677A

US3152677A - Electronic coin detecting device

Info

Publication number: US3152677A
Application number: US142210A
Authority: US
Inventors: William C Phillips
Original assignee: STONER INVESTMENTS Inc
Current assignee: STONER INVESTMENTS Inc
Priority date: 1961-10-02
Filing date: 1961-10-02
Publication date: 1964-10-13
Anticipated expiration: 1981-10-13

Description

1964 w. c. PHILLIPS 3,152,677

ELECTRONIC com DETECTING DEVICE Filed-Oct. 2. 1961 2 Sheets-Sheet 1 vvvI I 'I'I'A INVEN TOR. WILLIAM C. PHILLIPS ATTY.

Oct. 13, 1964 Filed Oct. 2. 1961 W. C. PHILLIPS 2 Sheets-Sheet 2 E WWW? r A ;5 COIN DETECTING D cmcurr 3 5E COIN DETECTING EE- cuzcun z WMMMT cow l DETECTING gg 'i cmcun I g I; #1

INVENTOR. WILLIAM C. PHILLIPS United States Patent O r 3,152,677 ELECTRONIC COIN DETECTING DEVICE William C. Phillips, Aurora, Ill., assignor to Stoner Investments Inc., Aurora, Ill., a corporation of Illinois Filed Oct. 2, 1961, Ser. No. 142,210

9 Claims. (61. 194-100) This invention relates in general to an electronic detecting device and, in particular, to a detecting device for accepting desired objects and rejecting unwanted objects.

More specifically, the invention may be applied to coin detecting devices where it is desired to accept coins of various denominations and reject coins both foreign and domestic of other denominations. It is also desirous to reject slugs, cut-down and filed coins and the like.

A general object of this invention is to provide an improved electronic detecting device.

It is one specific object of this invention to provide an improved electronic detecting device capable of accepting desired metallic objects and rejecting other objects.

Another specific object of this invention is to provide an improved electronic detecting device capable of accepting desired objects and rejecting other objects.

A more specific object of this invention is to provide a coin detecting device that contains a single coin chute for accepting coins of various denominations and which tests the incoming coins for acceptance or rejection as the coins continuously pass through the coin chute.

Another specific object of this invention is to provide a coin detecting device that is quick in operation and can therefore accept or reject inserted coins rapidly, enabling more coins to be eflfectively fed into the device in a shorter length of time.

Another specific object of this invention is to provide a coin detecting device that can accept coins of various denominations and which utilizes the electrical properties of the inserted coins to influence appropriate tests circuits which in turn cause the inserted coins to be accepted or rejected.

Another specific object of this invention is to provide a coin detecting device that can accept coins of various denominations and which is responsive to accept the in serted coin only when the inserted coins are in a predetermined position thus eliminating a source of error that could arise when a coin of one denomination influences the test circuit like a coin of another denomination because of its space position with respect to the provided coin detecting means.

It is another specific object of this invention to provide a coin detecting device that can accept coins of various denominations and which is readily and easily converted to accept coins of other denominations including foreign coins by simple circuit adjustments.

It is yet another specific object of this invention to provide a coin detecting device that is tolerant of circuit parameter changes without reducing the sensitivity of the device itself.

Briefly, in a preferred embodiment of the invention, a coin detecting device is provided that can accept coins of various denominations. The device contains a single coin opening, a single non-conducting coin chute and a single coin sensing position. A pair of coils connected in a bridge circuit and positioned adjacent the coin chute are arranged to provide a signal whenever the inserted coin is in the coin sensing position. The inserted coins move continuously in the coin chute and are therefore only momen- 3,152,677, Patented 0st. 13, 1964 circuits are adjusted to provide a predetermined output signal when a coin corresponding to each of the coin detecting circuits is in the coin sensing position. If a coincidence of signals occurs, one from the coin positioning circuit and one from any of the coin detecting circuits, means are energized by the corresponding coin detecting circuit to accept the incoming coin. If no such coincidence of signals occur the inserted coin will pass through the coin detecting device and he therefore rejected.

Further objects and features of the present invention will become more apparent if the following is taken in view of the accompanying drawings of which:

FIG. 1 is a diagrammatic illustration of the geometric positioning of the electromagnetic coils utilized in the illustrated embodiment of the invention;

FIG. 2 is another diagrammatic illustration as in FIG. 1 but from substantially the front view;

FIG. 3 is a portion of the schematic drawing illustrating an embodiment of the invention; and

FIG. 4 is the remainder of the schematic drawing illustrating an embodiment of the invention.

The general sensing scheme utilized in the invention is to arrange electromagnetic coils having an input signal frequency much higher than the line voltage in proximity to a coin chute of a coin detecting device. The presence of a coin in the coin chute will change the apparent impedance of these coils and the amount of change depends on the type of material, size, shape, temperature, and position of the particular coin in the coin chute. The change in impedance of the electromagnetic coils is utilized to provide electrical signals which, under the proper circumstances, accepts the coin.

Because of the fact that the change in impedance of the coils varies with so many factors it is possible that a small coin in one position in the coin chute would appear as a big coin would in a second position in the coin chute and much confusion and resultant error will occur. Therefore, the coin detecting device is arranged to only accept an. incoming coin if that coin changes the impedance of the coils a predetermined amount when in a specific and predetermined position.

Referring now to the drawings, there is illustrated an alternating current generating circuit 10, a coin position indicating circuit 20 and a plurality of

coin detecting circuits

30, 40 and 50. The coin position indicating circuit 20 performs the function of generating a signal, which in the illustrated embodiment of the invention is a null voltage, whenever an inserted coin passes through a coin sensing position in the coin chute. The alternating current generating circuit 10 in the illustrated embodiment of the invention, generates a signal of approximately 50,000 cycles per second and delivers this signal to both the coin position indicating circuit 20 and the plurality of

coin detecting circuits

30, 40 and 50. The plurality of

coin detecting circuits

30, 40 and 50 perform the function of generating a signal, which in the illustrated embodiment of the invention is a null voltage, whenever a coin corresponding to the particular coin detecting circuit is in the coin sensing position and to also activate coin acceptance means when the coincidence of a null voltage from the coin position indicating circuit 20 and the particular coin detecting circuit occurs.

The coin position indicating circuit 20 comprises a four terminal bridge circuit 201, a first amplifier stage 202, a second amplifier stage 203 and a portion of a peak detector circuit 204, as will be seen.

The bridge circuit 201 comprises a pair of oppositely wound electromagnetic coils L4 and L5 and a pair of

equal value resistors

205 and 206. Equal valued and oppositely polarized signals from the alternating current generating circuit 10 are coupled to the coils L4 and L5 as will be described later. Therefore, whenever the apparent imr 3 pedance of the coils L4 and L5 are equal, there is no output signal across the terminals a and b. After a coin is inserted into the coin chute 60 it has some effect on the impedance of the coils L4 and L5 and this effect is not equal on both these coils and therefore a signal appears at the terminals a and b of the bridge cricuit 201.

As an inserted coin passes down the coin chute 60 it goes through a position where it is symmetrically positioned between the coils L4 and L5 and when in this position there is no output signal provided across the terminals a and b of the bridge circuit 201. When an inserted coin produces this absence of signal or null voltage, the coin is said to be in the coin sensing position in the coin chute 60. When the coin is in the coin sensing position the coin detecting circuits test to determine whether the coin corresponds to the denominations to which they are set and if the coin does so correspond, means are activated to retain the coin in the coin detecting device as will be seen.

later.

The

amplifier stages

202 and 203 amplify the signal which appears across the terminals a and b of the bridge circuit 201 and can be of any standard type of arrangement and for that reason, and so as not to obliterate the inventive concept, are not described. The output signal from the second stage amplifier 203, which is an AC. signal inasmuch as the input to the bridge circuit 201 is an AC. signal, is transmitted to the peak detector circuit 204 through the AC. coupling capacitor 207. The peak detector circuit 204 is connected to all three

coin detecting circuits

30, 40 and 50 and shares a

common storage capacitor

210, 210 and 210 with each of the

coin detecting circuits

30, 40 and 50, respectively. The values of the resistors 20%, 211, 211 and 211" and the

capacitors

210, 210' and 210 along with the input impedances of the

transistors

212, 212 and 212" are all selected to enable the rectifier 209 to cause a voltage equal to what would be the envelope of the AC. output signals from the second amplifier stage 203 to appear across the

capacitors

210, 210' and 210 and the base-emitter circuits of the

transistors

212, 212' and 212". The detailed operation of a peak detector circuit is well known and can be readily found by consulting any good textbook.

The frequency generating circuit comprises an oscillator circuit 101 and an isolating cathode follower circuit 102. The oscillator circuit 101 can be of any well known type and can, for example, be of the type disclosed in Transistors in Radio & Television by M. S. Kiver, on or about page 296, and the frequency of oscillation can be adjusted by adjusting the variable inductor L1. It may be found that, depending upon the material composition of the coins to be accepted, the oscillator frequency must'be changed to provide optimum results. Good results have been found when the oscillator circuit 101 is adjusted to provide an output of approximately 50,000 cycles per second, in the disclosed embodiment of the invention. The cathode follower circuit 102 can be of any standard type and will not be explained in detail here and it serves the function of impedance isolating the output of the oscillator circuit 101 from variations in impedance caused by the

coin detecting circuits

30, 40 and 50 as will be seen later. The output of the cathode follower circuit at A is represented in the drawings and is a 50,000 cycle sine wave and is connected to each of the

coin detecting circuits

30, 40 and 50 as above shown and is magnetically coupled to the coin positioning circuit as will be explained. l

The

coin detecting circuits

30, 40 and 50 in the illustrated embodiment of the invention can, for example, correspond to dimes, nickles and quarters, respectively, and each circuit is designed to provide a null voltage or minimum output when a coin corresponding to its pre-assigned denomination is present in the coin sensing position previously described in the coin chute 60.

It should be noted that if a coin appears to one of the coin detecting circuits as the coin to which it is assigned when the coin is in any position but the coin sensing position in the coin chute 60, no effect will occur inasmuch as there must be a coincidence of a coin in the coin sensing position plus the recognition of the coin by the coin detecting circuits before the coin can be accepted as will be explained more fully later.

Each of the

coin detecting circuits

30, 40 and 50 are provided with a

bridge circuit

301, 401 and 501, respectively. The electromagnetic coil L3 and the

resistors

302 and 303 are common to each of the

bridge circuits

301, 401 and 501. The electromagnetic coil L3 has the output voltage from the signal generating circuit 10 applied thereto as can be seen in the drawings. The coil L3 is symmetrically positioned on the opposite side of the coin chute 60 as can be seen in FIGS. 1 and 2. The coin chute 60 is formed of some non-conducting materal such as plastic so that the coil L3 will be magnetically coupled to coils L4 and L5, thus supplying voltage to the coin positioning circuit 20 as previously mentioned. Coil L3 feeds equal voltages to both coils L4 and L5 but coil L5 is wound oppositely to coil L4 and therefore equal and opposite voltages appear across coils L4 and L5.

The

bridge circuits

301, 401 and 501 are each tuned by, for example, placing and holding a coin of a preselected denomination in the coin sensing position in the coin chute 60 and then tuning the variable inductance LZ'and variable resistor R until the bridge circuit 301 provides no output voltage across the terminals 0, d. Next a coin of a second pro-selected denomination can be placed and held in the coin sensing position in the coin chute 60 and then the variable inductance L2 and variable resistor R can be varied until the bridge circuit 401 provides no output voltage across the terminals 0, c. This same process can be repeated for coin detecting circuit 50 with the variable inductance L2" and variable resistor R" being tuned for a null across terminals c, 1 when a third coin of a pre-assigned denomination is placed in the coin sensing position in the coin chute 60. As can be readily seen additional circuits can be added to the

coin detecting circuits

30, 40 and 50 to accommodate additional coin denominations.

With the exception of the

bridge circuits

301, 401 and 501, the coin detecting circuits are substantially identical. Therefore, only one of these coin detecting circuits will be explained in detail. Coin detecting circuit 30, for example, is provided with a first amplifier stage 306 which can be of any standard type known in the art. The amplifier stage 306 is provided with the parallel series combination of resistor 307 and capacitor 308 to prevent undesired feedback to the amplifier stage 306 and similarly positioned components in the remainder of the circuits perform the same function. Following the amplifier stage 306 is the peak clipping circuit 309 which functions to clip the positive and negative peaks of the output voltage from the first amplifier stage 306 whenever the peak value of this output voltage exceeds a predetermined value. The provision of the clipping circuit 309 determines the sensitivity of the coin detecting circuit as will be explained later. The peak clipping circuit 309 can be of any well known type and can, for example, be of the type disclosed in Electronics magazine, October 7, 1960, page 72.

Following the output of the peak clipping circuit 309 of the coin detecting circuit 30 is the second amplifier stage 310 which again can be of any standard type and therefore need not be treated in detail. The second amplifier' stage 310 amplifies the output of the peak clipping circuit 309 and feeds its output voltage to its associated peak detector circuit 311. The peak detector circuit 311 takes the envelope of the output waveform from the second amplifier 310 and applies it to the input of the transistor 212. The peak detector circuit 311 comprises resistor 313, the rectifier 312 and the capacitor 210. The peak detector circuit 311 shares the capacitor 210 in common with the peak detector circuit 204 of the coin position indicating circuit 20. The peak detector circuit 311 can be chosen from those known in the art and the details thereof are not a part of this invention.

The transistor 212 which comprises what may be termed a form of switching circuit is normally cut-off. Cut-off voltage is applied to the input circuit of transistor 212 from the peak detector circuit 204 except when a coin is in the coin sensing position in the chute 60. When a coin is in the coin sensing position in the coin chute 60, a null voltage is created in the coin position indicating circuit 20 and consequently no output is provided by the peak detector circuit 204. Cut-otf voltage is normally applied to the input circuit of transistor 212 from the peak detector circuit 311 except when the coin in the chute changes the apparent impedance of the coil L3 to such a degree as to correspond with the denomination coin to which the coin detecting circuit is assigned. When both the coin position indicating circuit 20 and the coin detecting circuit as for example 30 provide null output voltages then the transistor 212 will not be back biased and will conduct. Only under these aforementioned conditions will transistor 212 con duct and at all other times transistor 212 will be cut-01f.

A direct current amplifier 315 is connected directly to the collector of the transistor 212 and the direct current amplifier 315, which can be of any standard type, amplifies the output of transistor 212 whenever that occurs and feeds a monostable vibrator type circuit 316. The mono-stable vibrator type circuit 316 comprises a pair of transistors 330 and 331 and their associated components and an output relay K1. Normally, transistor 330 is conducting and transistor 331 is cut-off and consequently relay K1 is de-energized. Whenever a pulse is delivered to transistor 330 that cuts-oflf transistor 330, transistor 331 is turned on for a predetermined period of time to energize relay K1 to cause the coin passing through the coin sensing position in the coin chute to be accepted. Any appropriate well known mono-stable circuit can be utilized as, for example, one of the type disclosed in Transistor Circuits & Applications by J. M. Carrol, Assoc. Editor, page 72.

Operation Initially, the

coin detecting circuits

30, 40 and 50 are set as previously described. A coin to which, for example, coin detecting circuit 30 is assigned is placed and held in the mentioned coin sensing position symmetrically between the coils L4 and L5 and the variable inductor L2 is adjusted for'a null output on the bridge circuit 301 all as previously described. The

coin detecting circuits

40 and 50 are similarly set and then the coin detecting device is ready for service. It should be apparent that it is a comparatively simple matter to assign any desired coin, foreign or domestic, or for that matter any object, to any of the provided

coin detecting circuits

30, 40 and 50 and that re-assignment can be readily made on the scene even by one not expert in the maintenance of coin detecting devices.

1 It is desirable, although not absolutely necessary, to have the coins passing through the coin chute 60 to take the same path as-for example against one wall of the coin chute 60. This may be accomplished by inclining the coinchute-60 at the proper angle or by anyalternative measures.

Assume that a coin corresponding to the coin assigned to coin detecting circuit 30 is inserted into the coin chute 60. The effect that this coin has on each of the

coin detecting circuits

30, 40 and 50 is diagrammatically illustrated in the drawings at B, C, D and E.

When the coin first enters the coin chute 60 it has relatively no elfect on the impedance of the coin detecting coil L3 positioned adjacent the coin chute 60 as indicated in FIGS. 1 and 2, Consequently all of the

bridge circuits

301, 401 and 501 of the

coin detecting circuits

30, 40 and 50 are unbalanced and therefore their associated coin acceptance relays K K and K respectively, are not energized. The output voltage from each of the bridge circuits such as, for example, the bridge circuit 301 is first delivered to its first amplifier stage 306 where it is promptly amplified and appears as at B. Next the output of the first amplifier stage 306 is delivered to the peak clipper circuit 309 where the peak of the input waveform is clipped if the peak exceeds a predetermined amount. Next the output of the peak clipper circuit 309 is delivered to and amplified by the second amplifier stage 310 and the resultant Waveform can be seen at C. The output of the second amplifier stage 310 is delivered to the peak detector circuit 311 which provided an output waveform corresponding to the en velope of the incoming waveform and in essence takes an amplitude varying AC. input and provides a corresponding amplitude varying DC. output. The output from the peak detector circuit 311 is stored across the capacitor 210 and back biases the transistor 212. The peak detector circuit 204 in the coin position indicating circuit 20 also stores its output across capacitor 210 and also back biases the transistor 212. Therefore, before the transistor 212 can conduct an absence of signal from both the peak detector circuit 311 and the peak detector circuit 204 must occur. At this time, with the bridge circuit 301 unbalanced, transistor 212 is cut-off consequently cutting 011 the DC. amplifier stage 315. The absence of an output from the D.C. amplifier stage 315 maintains the output stage of the mono-stable multivibrator circuit 316 cut-off and consequently the coin acceptance relay K de-energized. Substantially the identical situation occurs in both the

coin detecting circuits

40 and 50 at this time and their respective coin acceptance relays K and K are also de-energized.

As the coin approaches the coin detecting coil L3, the eliect on each of the

bridge circuits

301, 401 and 501 is different. The output of the bridge circuit 301 gradually decreases until a null is provided. This null occurs just at the time that the coin is positioned directly in front of coil L3 symmetrically between the coils L4 and L5 and this is what is known as the coin sensing position. The resulting null or balance of the bridge circuit 301 and the bridge circuit 201 causes the transistor 212 to turn on and to consequently turn on the DC. amplifier stage 315. The DC. amplifier stage 315 sends a pulse to the mono-stable multi-vibrator circuit 316 that causes the multi-vibrator circuit to turn on to provide an output pulse to the coin acceptance relay K as illustrated at E. The variable resistor 211 in the peak detector circuit 204 is used to prevent overloading of the following stages. The multi-vibrator 316 is adjusted to fire or to turn on when the null is reached and that is when the output of the transistor 212 as shown at D and consequently the output of the DO. amplifier 315 is at its greatest. The energization of the coin acceptance relay K causes the coin passing through the coin chute 60 to be retained in the coin detecting device by means not shown and not forming a part of this invention.

The effect of the chin approaching and leaving the coin sensing position previously described on the

coin detecting circuits

40 and 50 is quite different. The approach of the coin diminishes the output of the bridge circuit 401 of the coin detecting circuit 40 but not enough for a null and even above the clipping level so that no efiect whatsoever is present after the clipping stage, as can be seen at C in the coin detecting circuit 40.

The bridge circuit 501 of the coin detecting circuit 50 behaves entirely different again. The approach of the coin influences the bridge circuit 501 so radically as to balance the bridge circuit 501 before the coin reaches the coin sensing position thus having no etfect'because of the absence of the coincidence of nulls necessary as previously discussed. The bridge circuit 501 then becomes unbalanced again as the coin approaches the coin sensing position so that when the coin position indicating circuit provides a null the output from the coin detecting circuit 50 prevents the coin acceptance relay 50 from energizing. The bridge circuit 5131 again goes to a null after the coin has passed the coin sensing position but as can be readily understood this will have no effect on the coin acceptance relay K Because of the bridge type impedance detection employed in this invention the signal generating circuit 19 can vary in frequency to some degree without effecting the operation of the coin detecting device.

What has been described is what is considered to be the preferred embodiment of the invention and many alterations and modifications can be made without departing from the inventive concept of the invention.

What is claimed in the United States Letters Patent is:

1. In a coin detecting device a coin position indicating circuit providing a first recognition signal when a coin passes through a coin sensing position, a plurality of coin detecting circuits for detecting coins pre-assigned to said coin detecting circuits and each coin detecting circuit providing a coin detecting recognition signal whenever a coin is present that electrically corresponds to any of their pre-assigned coins, and coincidence means in each of said coin detecting circuits responsive to the presence of said first recognition signal and the presence of its own coin detecting recognition signal for registering the presence of any of said pre-assigned coins.

2. In a coin detecting device a coin position indicating circuit providing a first recognition signal when a coin passes through a coin sensing position, said coin position indicating circuit comprising, a pair of electromagnetic coils operably positioned in said coin detecting device so as to be equally aifected by an incoming coin only when said coin is in a predetermined position, and means responsive to the equal etfect provided by said pair of coils for providing said first recognition signal, a plurality of coin detecting circuits for detecting coins pre-assigned to said detecting circuits and each coin detecting circuit providing a coin detecting recognition signal whenever a coin is present that electrically corresponds to any of their pre-assigned coins, and coincidence means in each of said coin detecting circuits responsive to the presence of said first recognition signal and the presence of its own coin detecting recognition signal for registering the presence of any of said pre-assigned coins.

3. In a coin detecting device a coin position indicating circuit providing a first recognition signal when a coin passes through a coin sensing position, a plurality of coin detecting circuits for detecting coins pre-assigned to said coin detecting circuits and each coin detecting circuit providing an additional coin detecting recognition signal whenever a coin is present that electrically corresponds to any of their pre-assigned coins, said plurality of coin detecting circuits each having in common a single electromagnetic coil operably positioned so as to be aliected by the electrical characteristics of a coin present in said coin detecting device, means in each of said coin detecting circuits responsive to the changes in said single coil to provide any one of said additional coin detecting recognition signals whenever said changes correspond to the changes that occur when a coin corresponding to any one of the pre-assigned coins of the coin detecting circuits is present, and coincidence means responsive to the presence of said first recognition signal and one of said additional recognition signals for registering the presence of the respective pre-assigned coin.

4. A coin detecting device comprising a coin passageway,

a pair of mutually spaced coils located adjacent said passageway, a third coil intermediate said pair of coils, oscillator means for applying a sinusoidal signal to said coils, coin position circuit means connected to said pair of coils for transmitting said signal with a predetermined modulation in response to the attainment by a coin of a predetermined position,

a plurality of coin detecting circuit means each connected to said third coil for transmitting said signal with a predetermined modulation in response to the presence of a coin of pre-assigned electrical characteristics,

means for selectively adjusting each of said coin detecting circuit means so as to pre-assign the electrical characteristics to which each detecting circuit means will respond,

and means for registering the presence of a coin of preassigned electrical characteristics in response to the simultaneous transmission of said signal With said predetermined modulations by said coin position circuit means and by one of said coin detecting circuit means.

5. A coin detecting device comprising oscillator means for generating a sinusoidal signal,

coin position circuit means for transmitting said signal with a predetermined modulation in response to the attainment by a coin of a predetermined position,

a plurality of coin detecting circuit means for transmitting said signal with a predetermined modulation in response to the presence of a coin of preassigned electrical characteristics,

means for selectively adjusting each of said coin detecting circuit means to pre-assign the electrical characteristics to which each detecting circuit means will respond,

and means for registering the presence of a coin of pre-assigned electrical characteristics in response to the transmissions of said signal with said predetermined modulations by said coin position circuit means and by one of said coin detecting circuit means.

6. A coin detecting device comprising a coin passageway,

a pair of mutually spaced coils located adjacent said passageway,

a third coil intermediate said pair of coils,

oscillator means for applying an electrical signal to said coils,

coin position circuit means connected to said pair of coils for transmitting said signal with a predetermined modulation in response to the attainment by a coin of a predetermined position,

and means for registering the presence of a coin of pre-assigned electrical characteristics in response to the transmission of said signal with said predetermined modulations by said coin position circuit means and by one of said coin detecting circuit means.

7. A coin detecting device comprising oscillator means for generating an electrical signal,

a plurality of coin detecting circuit means each for transmitting said signal with a predetermined modulation in response to the presence of a coin of respective pre-assigned electrical characteristics,

and means for registering the presence of a coin of pre-assigned electrical characteristics in response to the simultaneous transmissions of said signal with said predetermined modulations by said coin position circuit means and by one of said coin detecting circuit means.

8. A coin detecting device comprising a coin passageway,

a pair of mutually spaced coils located adjacent said passageway,

a third coil intermediate said pair of coils,

oscillator means for applying a sinusoidal signal to said coils,

coin position circuit means connected to said pair of coils for transmitting said signal and including a bridge circuit for nulling said transmitted signal in response to the attainment by a coin of a predetermined position,

a plurality of coin detecting circuit means each connected to said third coil for transmitting said signal and including a bridge circuit for nulling said transmitted signal in response to the presence of a coin of pre-assigned electrical characteristics,

means for selectively adjusting each of said coin detecting circuit means so as to pre-assign the electrical characteristics to which each detecting bridge circuit will respond by nulling the transmitted signal,

and means for registering the presence of a coin of preassigned electrical characteristics in response to the simultaneous nulling of said transmitted signals by said coin position bridge circuit and by one of said coin detecting bridge circuits.

9. A coin detecting device comprising oscillator means for generating a sinusoidal signal,

coin position circuit means for transmitting said signal and including a bridge circuit for nulling said transmitted signal in response to the attainment by a coin of a predetermined position,

a plurality of coin detecting circuit means for transmitting said signal and including a bridge circuit for nulling said transmitted signal in response to the presence of a coin of pre-assigned electrical characteristics,

and means for registering the presence of a coin of preassigned electrical characteristics in response to the nulling of said transmitted signals by said coin position bridge circuit and by one of said coin detecting bridge circuits.

References Cited in the file of this patent UNITED STATES PATENTS 2,504,731 Rose Apr. 18, 1950 2,849,115 Tooker Aug. 26, 1958 2,992,731 Edclman July 18, 1961 FOREIGN PATENTS 765,071 Great Britain Jan. 2, 1957