DE3485866T2 - DEVICE FOR DETECTING THE VALIDITY OF COINS. - Google Patents

Description

This invention relates to coin validation devices and is particularly, but not exclusively, concerned with such coin validation devices which consume very little power and which are therefore suitable for use in, for example, coin telephones.

US-A-4 124 111 discloses coin validation devices in which the outputs of inductive sensors are applied to window comparators to determine whether the peak values of the outputs are within predetermined limits. Timers are also provided to determine whether the period of time during which the sensor output exceeds a predetermined threshold level is within predetermined limits. Another embodiment disclosed in US-A-4 124 111 is intended to avoid problems due to the possibility of a counterfeit coin producing the same peak value in the sensor output as a genuine coin. In this other embodiment, a level sensor causes counting pulses to be generated during the period of time during which the sensor output exceeds a certain threshold. The sensor output is digitized and the counting pulses cause successive digitized outputs which are added up in a counter. The final counter output thus represents the integral of the sensor output level over the period in which the sensor output exceeds the threshold level.

It is therefore the objective of this embodiment to validate coins based on the total area under the curve representing the sensor output level, regardless of whether specific output level values are reached. However, it is very often desirable to perform the validation of coins based on whether a specific portion of the output level curve, particularly the peak, attains a predetermined value.

In accordance with the invention there is provided a coin validation device for determining whether an object is a genuine coin, the validation device comprising a sensing device comprising a coin validation sensor and a validation circuit coupled to an output of the sensing device for calculating a coin measurement based on the sum of values indicative of successive amplitudes of an output signal from said sensing device produced when said object moves relative to said sensor and for determining whether said measurement is suitable for a genuine coin, characterized in that the measurement is carried out based on the sum of values indicative of successive amplitudes of said output signal produced while the object is substantially in a position at which a peak level of the output signal amplitude occurs, the measurement being representative is for the mentioned top level.

Preferably, the coin measurement is based on the first n of a larger number of values read by the circuit, but not on each subsequent reading. Preferably, the measurement is based on selected initial values, wherein the means for detecting validity comprises circuitry responsive to the sensor output values for detecting when a coin leaves the sensor and for selecting the values on which the measurement is based in dependence thereon.

Preferably, a predetermined number of measurements are stored and when the most recent measurements indicate that the coin leaves the sensor, the first n of these measurements are averaged, where n is a predetermined value.

EP-A1-0 058 094 describes a device for detecting the validity of coins which provides very accurate and reliable results and which consumes very little power. Preferred aspects of the present invention are concerned with further improvements in this field and are largely aimed at reducing the cost of the device without increasing the power consumption.

It is known, for example, from EP-A1-0 058 094 to provide an arrival sensor used to measure when a coin arrives at a validation device in order to energise the parts of the validation device circuitry which are normally either switched off or run at a relatively low current level to save power.

Preferably, a coin validation device of the present invention comprises an arrival sensor for sensing the arrival of a coin at a sensing station and a processor having a first state in which it performs processing operations and operates at a relatively high power level and a second state in which it operates at a relatively low current level, and means for periodically causing the processor to enter the first state to determine, using said arrival sensor, whether a coin has arrived. Preferably, the processor is caused, in its first active state, to perform a validity checking operation in response to the arrival of the coin when detected by the arrival sensor. The processor is preferably a microprocessor.

Preferably, the arrival of a coin is determined by a periodic measurement using an arrival sensor and to determine that a coin has arrived when the measurements produce values that vary in a predetermined manner. In a preferred embodiment, the last two measurements taken from the frequency of the output of the arrival sensor are considered and if this frequency is found to have increased by more than a predetermined amount, it is determined that a coin has arrived at the sensor. This determination is made in dependence on measurements taken over a short period of time and therefore the effects of any shift occurring due to, for example, temperature changes or ageing of the components do not have any significant effect on the determination of the arrival of a coin.

The processor is preferably activated periodically only long enough to take a measurement and determine whether a coin has arrived. The processor then returns to its second state to reduce power consumption unless the arrival of a coin is detected, in which case the process of detecting validity is performed.

Preferably, circuitry is provided to automatically reset the processor after the processor has been caused to enter its active state, unless the circuitry is prevented from doing so by the processor itself. Under normal circumstances, the processor will prevent the reset circuit from operating, but if the processor "hangs", i.e., ceases to operate properly, then it will automatically reset so that proper operation of the processor can be restarted. The reset circuit may also be arranged to respond to other signals; for example, it may respond to an output of the processor and cause the reset if a signal from the output lasts longer than a predetermined interval.

In a preferred embodiment, a counter is arranged to count upon activation of the processor and to cause resetting when a predetermined count is reached. Under normal circumstances, the counter would be cleared by the processor before this predetermined count is reached. The counter may also be used to periodically cause the processor to enter its first state.

The arrival sensor output can be measured by using a counter (possibly the counter mentioned above) which is caused to count the arrival sensor oscillations for a predetermined period of time to produce a count value representing a frequency. This method can also be used during the validation process to produce a measurement of a parameter (preferably the diameter) of the coin.

Preferably, the coin validation device does not normalize the speed of coins delivered to a sensing station thereof and includes means responsive to a value indicative of the speed at which a coin passes through the sensing station for generating a signal indicating that the coin cannot be accepted in response to a determination that the coin has passed through the sensing station too quickly.

Coin speed can be determined by measuring the distance between the passage of the coin through two separate sensors and/or by measuring the rate of change of an output signal from a single sensor. Such an arrangement is particularly valuable in small coin validation devices where the distance between a coin entry slot and the coin sensors is short and therefore there is a high risk that the movement of the coin by the time it reaches the sensor has not yet stabilized to a sufficient extent to ensure accurate validation results.

US-A-3 797 628 discloses a coin validation device in which token velocity is measured to determine whether a coin is acceptable. However, this deals with a different type of validation device in which the velocity of an inserted coin is normalized and then varied in accordance with the characteristics of the coins so that the velocity measurement is in effect a test of the coin rather than a check of whether the case of the coin is suitable for validation.

Arrangements embodying the invention will now be described by way of example with reference to the accompanying drawings in which:

Fig. 1 schematically shows a coin channel of a device for detecting the validity of coins in accordance with the invention,

Fig. 2 is a schematic diagram of the device for detecting the validity of coins,

Fig. 3 is a circuit diagram of an arrival sensor of the validity detection device,

Fig. 4 is a circuit diagram of a material sensor in a modified embodiment of the device for detecting validity,

Fig. 5 is a schematic diagram of the circuit of the modified embodiment, and

Figures 6A and 6B are views, respectively, of opposite sides of a printed circuit board carrying a test coil used in each embodiment of the validity detecting device.

Referring now to Figures 1 and 2, the validation device 2 comprises a main processor 4 which uses an arrival/diameter sensing circuit 6 and a material/thickness sensing circuit 8 to detect the arrival of coins, to test those coins and to provide signals indicating whether a coin is genuine and, if so, the type of coin.

The arrival/diameter sensing circuit 6 comprises a sensing coil 10 connected in an oscillator circuit to be described in more detail below.

The coil 10 is located at one side of a coil channel 7. The channel 7 is inclined and slanted so that coins, such as that shown at 9, travel down the channel 7 in the direction A with their faces in contact with the side of the channel on which the coil 10 is located. The circuit 6 is arranged so that the signal arriving at the output 12 of the circuit 6 has a frequency which changes as a coin passes the coil 10 and these peaks at a level depend predominantly on the diameter of the coin.

The material/thickness sensing circuit 8 comprises a coil 14 located on the side of the coin channel 7 opposite to the coil 10. The coil 14 is connected in an oscillator circuit and the circuit is arranged so that the signal appearing at the output terminal 16 is attenuated in response to a coin passing through the coil 14. The peak value of the attenuation is predominantly dependent on the material from which the coin is made and on the thickness of the coin. Because the coin contacts the side of the channel 7 opposite that on which the coil 14 is located, the distance of the coin from the coil will depend on the coin thickness, thus ensuring that this has a significant effect on the output of the circuit 8.

Processor 4 is a CMOS 8048 (or CMOS 8049) microprocessor. It has terminals P1, P2, P3, P4 and P5 which are respectively a count output terminal, an interrupt input terminal, a reset input terminal, an input/output terminal and a testable input terminal. There are also address/data bus terminals D. The remaining terminals, referred to below, are additional input/output terminals which, other than terminal P4 which is used as both an input and an output at different times, are only required to perform a single input or output function in the particular circuit shown. The processor 4 also includes power supply terminals, count input terminals, etc., which are not shown in Fig. 2.

The processor 4 has in its set operating instructions a HALT instruction which, when executed, causes the processor to enter a sleep state in which no process operations are performed and power consumption is significantly reduced. The processor can be switched back to an active state by a signal at the interrupt terminal P2.

The validation device is mounted in a pay phone. Under normal circumstances, the entire validation device is switched off. When the handset is raised, parts of the validation circuit are switched on together with the processor 4 and the arrival/diameter sensing circuit 6, but excluding the material/thickness sensing circuit 8.

The processor 4 then performs a routine start-up procedure, after which a HALT instruction is executed so that the processor enters an idle state.

The oscillations appearing at the output terminal 12 of the arrival/diameter sensing circuit 6 are applied through gates 18 and 20 to the count input 22 of a counter 24. The counter has output terminals C1 through C10. The counter counts the pulses until a signal appears at the count output C10. This signal is applied to the interrupt terminal P2 of the processor 4 to cause the processor to enter its active state. The processor then proceeds to apply a clear signal on line 26 which is applied to the clear terminal 28 of the counter 24. The processor also applies a signal on line 30 to close the gate 18.

The processor 4 then temporarily opens the gate 18 for a predetermined period. The counter 24 is thus caused to count the pulses appearing at the output terminal 12 of the circuit 6. The last count occurring at the count terminals C1 through C8 is noted by the processor 4, which has input/output terminals connected to those count terminals, before the counter 24 is cleared by the processor.

The processor 4 has a memory into which the count is stored, the arrangement being such that the memory constantly stores the previous count measured in this way. The processor determines that a coin has arrived at the coil 10 when the second count exceeds the first by more than a predetermined number. Thus, a coin is detected in response to an increasing frequency appearing at the output terminal 12.

Assuming that no coin was detected, the processor 4 opens the gate 18 after clearing the counter 24 and executes the HALT instruction. The processor 4 will then enter its idle state until another signal appears at the counter terminal C10.

The processor is thus periodically caused to enter its active state to determine whether or not a coin has arrived, and if not the processor re-enters its idle state. This may occur at intervals of, for example, 5 milliseconds, with the processor being active for a period of less than 1 millisecond during each of these intervals. The average power consumption of the processor 4 is thus low.

Assuming that the arrival of a coin is detected, the processor 4 continues to check the frequency of the signal arriving at terminal 12. The frequency increases continuously until a peak is reached, after which the frequency decreases again until an idle level is reached, after which the coin has left the coil. The processor 4 detects and stores the peak and idle levels and then calculates the ratio of these two levels to produce a value indicative of the diameter.

At some stage, in response to detecting the arrival of a coin, the processor issues a signal on line 32 to operate a power switch 34. This causes a power supply to be connected to the material/thickness sensing circuit 8.

The processor 4 may be arranged to switch on the material/thickness sensing circuit 8 immediately after detecting the arrival of a coin to ensure that the operation of the circuit 8 has stabilized by the time the coin reaches the coil 14. For However, to save power, the processor 4 can also be arranged to switch on the circuit 8 after detecting the peak in the output frequency of the signal at the terminal 12 or possibly only when the processor 4 has detected that the frequency has dropped back to an idle level.

As a further possibility, the processor 4 can be arranged to check whether the diameter value matches a genuine coin of a value that the validation device is arranged to accept before switching on the circuit 8. In this way, the circuit 8 is only operated when the coin has an acceptable diameter and therefore the power consumption is further reduced.

When the diameter value is calculated and the circuit 8 is turned on, the processor 4 issues a signal on line 30 to close the gate 18 so that no further pulses from the circuit 6 can reach the counter 24. The counter is cleared and the processor issues a signal on line 36 to open a gate 38. This allows the gate to pass pulses from the terminal P1 through the gate 20 to the count input terminal 22 of the counter 24.

The counter 24 thus counts up at a constant, predetermined speed. The counting terminals C1 to C8 are connected via resistors R1 to R8 to respective points on a resistor series network R9 to R16, which is coupled between ground and one input 40 of a comparator 42. The other input 44 of the comparator 42 is connected to the output terminal 16 of the circuit 8.

Resistors R1 through R16 act as potential dividers in such a manner that a signal at any of the count output terminals C1 through C8 will produce a voltage at input terminal 40 of comparator 42 corresponding to the corresponding count terminal. The effect of this is to cause the voltage at terminal 40 to increase progressively in steps as the count achieved by counter 24 increases. The resistors have a close tolerance to ensure that an even distribution of voltages is produced as the count increases.

After the processor has output the signal from port P4 which opens gate 38, the port is switched so that it now behaves as an input port. As the voltage at input port 40 of comparator 42 increases, it will eventually rise above the voltage at port 44 from circuit 8. At this point, the output of comparator 42 will turn on logic levels, thus closing gate 38 and preventing further pulses from reaching counter 24. This change in logic levels is also output to port P4 of processor 4 which is detected by processor 4 and used to indicate that the count output ports C1 through C8 should be read. The count will be a digital representation of the analog voltage at port 16 of circuit 8.

The counter 24 is then cleared, the terminal P4 is switched to behave as an output terminal, and the gate 38 is again opened to allow the processor 4 to make another measurement of the output signal appearing at terminal 16 of the circuit 8.

The comparator 42 has an open collector output so that it and the terminal P4 can be connected directly to the gate 38, each being able to control the gate 38 without interfering with each other.

The processor 4 repeatedly measures the output appearing at terminal 16 and determines the blank value from these measurements. This is done before the coin reaches the sensing coil 14 and can be triggered by the circuit 6 sensing the movement of the coin away from the coil 10. Then, as the attenuation increases during the movement of the coin past the sensor, the peak value of the signal is determined. This is preferably achieved by storing successive readings. The processor detects when these values change in such a way that they indicate that the attenuation is decreasing as a result of the coin leaving the sensor. The processor then averages the stored values, preferably ignoring the more recent measurements so that the values used represent measurements taken when the coin was substantially at the midpoint of its movement past the sensor. For example, the processor may be arranged to determine the average of the first, say, four of the last twelve measurements. Of course, instead of taking an average measurement by summing a predetermined number of values and then dividing by that number to compare the resulting value with a stored value, the processor could simply sum the values without dividing the results; the stored ranges would be correspondingly larger.

The ratio between blank and peak is determined to produce a value that is indicative of thickness/material. The blank is measured before the peak so that the decision whether an accept/reject gate should be opened can be made very soon after the peak is reached and therefore little space is required between the coil 14 and this gate.

At the end of the thickness/material testing operation, the circuit 8 is turned off, the counter 24 is cleared, and the gate 18 is reopened to allow the pulses appearing at the output terminal 12 of the circuit 6 to reach the counter 24.

For each of the coin denominations that the validator 2 is designed to accept, the processor 4 stores information defining a diameter range and a material/thickness range. For example, the processor 4 may store upper and lower limits of the respective ranges or may also store a single value from which the processor can calculate the appropriate range using a stored or predetermined tolerance.

The processor 4 compares the two measurements, i.e. the diameter value and the thickness/material value, with the ranges for the respective coins and determines that a valid coin of a particular denomination has been received if both values fall within the appropriate ranges for that coin denomination. In this case, the processor 4 generates an ACCEPT signal on one or both of the data lines 46 and a binary signal on lines 48 indicative of the denomination of the coin.

The coin validation device 2 is intended for installation in various types of machines, for example gaming machines. In some of these it is desirable for the machine to be able to accept a first range of coins (for example 5p, 10p, 20p and 50p coins in British denominations) and in other machines a different range (for example 10p, 20p, 50p and £1 coins). In order to provide all this without having to manufacture different types of validation devices, the validation device is arranged to recognise all five coins and to generate ACCEPT signals on lines 46 in accordance with the range of coin denominations within which a received coin lies. Thus, if a coin value of a received coin falls within both ranges (for example, for 10p, 20p and 50p coins), an ACCEPT signal is generated on both lines 46 and the coin value is indicated by the data on lines 48. If the coin value is only within one range (for example, 5p), then only one of the lines 46 (corresponding to the range of coin values) will carry the ACCEPT signal, while lines 48 will carry data representing the 5p coin value. If a coin value belonging to only the other range is received (for example, a £1 coin), then the same data can be generated on lines 48, but this time the ACCEPT signal will be generated on the other of the lines 46.

Accordingly, the same device for detecting validity can be fitted in any of the above types of machines and in each case it is merely necessary to select which of the lines 46 is to be used in accordance with the range of coin denominations which the machine is intended to accept.

There is a risk that the processor 4 may "hang", i.e. it may stop operating properly, for example as a result of electrical disturbances or interference. To avoid problems caused by this erroneous operation, the validity detection device 2 comprises a reset pulse generator 50 which generates a pulse of predetermined length to reset the processor 4 in the event that one of the three conditions which provide an indication of "hang" occurs.

As mentioned above, the output of counter terminal C10 is used to provide a signal to interrupt terminal P2 of processor 4, causing the processor to provide a signal on line 26 to clear counter 24. If this does not occur due to faulty operation of processor 4, then the counter will not be cleared and will continue to count in response to pulses from circuit 6. Finally, an output signal will appear at terminal C9 of counter 24, and the simultaneous occurrence of signals at terminals C9 and C10 will be detected by gate 52 which provides an actuation signal through gate 54 to circuit 50 to cause processor 4 to be reset.

The gate 54 has two further inputs connected to respective detection circuits 56 and 58. Each of these receives a signal at its input and delays that signal, but the signal appears at the output only if the input signal lasts longer than a certain amount of time. The circuit 56 is connected to the clear terminal 28 of the counter 24, so that if after a signal to clear the counter is issued, the processor suddenly begins to behave incorrectly, the signal at the clear input terminal 28 will last longer than it should and this is detected by the circuit 56 which outputs a signal via the gate 54 to the circuit 50 to cause the processor 4 to be reset.

The circuit 58 has its input connected to line 30 which carries the signal issued by the processor 4 to close the gate 18. The longest time that the gate 18 is closed occurs when the processor is measuring the output of the circuit 8. The delay of the circuit 58 is set to be longer than this time. If the processor 4 begins to behave incorrectly during the thickness/material measurement process and the gate 18 thus remains closed, this will be detected by the circuit 58 and will cause the processor to reset.

Even if the processor 4 begins to behave incorrectly, it can nevertheless correctly execute an interrupt routine triggered by the signal applied to the P2 port. To detect this situation, the processor 4 is arranged to set a number of internal flags while executing the arrival detection routine. During the interrupt routine, the processor 4 checks to see if these flags are set. If they are not, because the main routine was not executed correctly, the processor 4 executes an instruction that causes it to be reset.

The device for detecting validity is preferably designed in such a way that the coin measurements which are made provide well predictable results for given coin values, so that the parameter ranges, stored by the processor 4 need not be specifically worked out for each validity detector. However, to accommodate minor variations between validity detectors, as well as changes in a particular validity detector due to aging or drift, the sensing circuits 6 and 8 can be adjusted in frequency and/or gain to modify their outputs.

To facilitate adjustments, the processor 4 can be placed in a test mode by connecting a connecting line 59 between a power supply rail and the testable input terminal P5, which terminal is normally held at a low potential by a resistor R17 connected to ground. At the same time, the operator connects a device to the data lines D to display the potentials on these lines.

After switching the validator to the test mode, the operator inserts a coin of a particular denomination (e.g. 10p) and determines which signals are generated on data lines 46 and 48 in response thereto. The coin inserted is preferably specifically selected so that its characteristics are an average of the normal variations expected in coins of that denomination.

The processor 4 operates as described up to and including the input of the digital values representing the measurements made by the sensing circuits 6 and 8. At this time, the processor checks the terminal P5 and If it turns out to be high, the processor performs a test routine instead of continuing with the validity detection procedures described above.

In the test routine, the values derived from the sensing circuits 6 and 8 are compared with a special set of "test ranges" rather than the normal acceptance ranges. These test ranges correspond to those ranges used to determine whether an acceptable coin of the specific coin value (e.g. 10p) has been received, except that they are narrower than the acceptance ranges.

In the test mode, the output of the processor on data lines 46 and 48 is in a different format and has a different meaning than the outputs in the normal validation process. In the test mode, if both measured characteristics are within their respective test ranges as a result of the coin insertion, a high level logic signal is applied to all output lines 46 and 48. If the value derived from sensing circuit 6 exceeds or falls below the corresponding range, then lines 46 are caused to carry a binary value of "10" or "01" respectively. Similarly, if the value derived from sensing circuit 8 exceeds or falls below its corresponding test range, then the value produced on lines 48 is "10" or "01" respectively. An output value "0000" on lines 46 and 48 is reserved for those situations in which the sensing circuits 6 and 8 produce incorrect values which are clearly not merely due to poor adjustment (for example, values resulting from two coins being simultaneously subjected to detection a bad coin flight path, etc.) so that the operator will be able to take appropriate action.

Referring now to Fig. 3, the arrival/diameter sensing circuit 6 comprises the coil 10 connected in a Colpitt oscillator circuit. In the specific embodiment used here, an amplifier formed by a transistor 60 has a feedback loop comprising the coil 10 connected between its collector and base. The coil 10 is connected in series with an adjustment circuit comprising a variable resistor 61 connected in parallel with an inductor 63. Capacitors 62 and 64 are each connected between, on the one hand, a respective end of the circuit formed by the components 10, 61 and 63 and, on the other hand, ground. The variable resistor 61 is used for the adjustment made during the test mode.

Resistors 66, 68 and 70 are provided to bias the transistor 60 into conduction. The load on the transistor 60 is distributed between a collector impedance (formed by a resistor RL and an inductor LL) and the resonant circuit formed by components 10, 61, 62, 63 and 64.

Thus, the output voltage appearing across capacitor 62 depends to a large extent on the fixed impedance RL and LL. Thus, although the passage of a coin near coil 10 will cause some attenuation of this voltage, the amount of attenuation will be relatively small because the load impedance does not change, compared with a circuit such as that described in the above-mentioned British Patent Specification No. 2 093 620 is used, in which the coil is connected to the collector current path and therefore has a very significant effect on the output voltage. The inclusion of the inductor LL increases the stability of the output voltage with changes in frequency.

Accordingly, the circuit 6 can be arranged so that it normally consumes only a low level of current, but will nevertheless provide an output signal which does not disappear even when a coin is in close proximity to the coil 10. This makes the circuit particularly suitable for use in an arrival sensing circuit. In order to reduce cost and power consumption, the circuit is also used for measuring purposes, as mentioned above. It has been found that if the coil 10 is arranged in the manner appropriate for diameter measurement and the frequency of the output rather than the amplitude is used for measuring purposes, a good discrimination can be achieved with the same low operating current as is used for measuring arrival.

A modified version of the above embodiment will now be described with particular reference to Figures 4 and 5. This embodiment operates in a similar manner to that described above, and like reference numerals are used for like parts, except for those points set out below.

In the embodiment described above, the sensor circuit 8 produced an output whose amplitude was measured to provide an indication of the material and thickness of the coin. In the embodiment of Figs. 4 and 5, the sensor is used to provide an output which is predominantly dependent on the material of the coin and somewhat less dependent on thickness. In this case, two coils 14 and 14' (the latter is shown in phantom in Fig. 1) are provided on respective sides of the coin channel. As in the previous embodiment, the amplitude of the output of the sensing circuit 8 is used for measurement purposes; in the present embodiment, however, the frequency of the output is used as an additional measurement. In total, therefore, there are three measurements which are compared with respective stored ranges and, as a result, the rejection of non-genuine coins has become even more reliable.

Fig. 4 shows the circuit 8, which is also suitable for use in the first described embodiment. The circuit has a standard oscillator design using a transistor 100. The two coils 14 and 14', which are arranged in a field-supporting arrangement, are connected in series with one another and with a variable induction element 102. The induction elements are connected in the collector path of the transistor 100. The emitter path comprises a variable resistor 104.

The output of circuit 8 is displayed at point 106 and is taken from the collector of transistor 100. When a coin passes between sensors 14 and 14', both the frequency and amplitude of the output signal change.

These parameters can be adjusted using the variable inductor 102 and the variable resistor 104. Preferably, the frequency is adjusted first using the variable inductor 102 as this will also have an effect on the amplitude.

Referring now to Fig. 5, in this embodiment the microprocessor 4 is a member of the Motorola 6805 family. It has a number of ports which can be used as input or output ports. In the arrangement shown the ports I1 to I3 are used as input ports and the ports O1 to O11 are used as output ports.

The microprocessor has an internal counter which can be made to emit pulses at regular intervals so as to act as a timer whose operation can be started or stopped by the application of a signal to terminal T1. The counter can also be used to count pulses appearing at terminal T1. This internal counter is used in place of counter 24 of Fig. 2.

The microprocessor 4 can operate a switch 150 which selectively supplies the output pulses of the sensing circuit 6 to a divide-by-four circuit 152 formed of two flip-flops. The output of the circuit 152 is supplied to the terminal T1. The internal counter can thus be used to count pulses from the circuit 6 and thus measure the frequency of the output. The states of the flip-flops in the circuit 152 are determined on input lines I2 and I3 so that two additional bits of resolution can be obtained. When the counting operation is started, the circuit 152 is released from its set state by changing the signal appearing at the output terminal O5. After the measuring operation, the circuit 152 is maintained in a set state which allows the input terminal T1 to receive other signals as will be described.

In particular, the output of the sensing circuit 8 is fed to the terminal T1 via another microprocessor-controlled switch 154 so that the frequency of this output can be measured. In this case, the divide-by-four circuit 152 is not required since the coils 14, 14' are driven at a much lower frequency than the coil 10.

The output of the sensing circuit 8 is also supplied to a comparator 158 via a rectifying circuit 156. Another input of the comparator 158 is connected to a junction between a constant current charging circuit 160 and a capacitor 162. The charging circuit 160 can be turned on or off by an output terminal O2 of the microprocessor 4.

In operation, to measure the amplitude of the output of the sensing circuit 8, the microprocessor turns on the charging circuit 160 and at substantially the same time starts the internal counter operating in its timer mode. This causes the voltage on capacitor 162 to increase linearly. When this voltage is equal to that from the rectifying circuit 156, the output of the comparator 158 switches polarity, which is sensed at input terminal I1. The microprocessor senses this and determines the count reached by the internal timer, which is the digital representation of the amplitude of the output of the sensing circuit 8.

The output of comparator 158 is fed to the timer terminal T1 through a microprocessor controlled switch 164. This is to ensure that the operation of the timer is stopped immediately after the output of comparator 158 changes state; this avoids problems caused by the delay in the microprocessor which first detects the change in the state at terminal I1 and then stops the timer.

Thus, the internal counter measures (a) the frequency of the output of the sensing circuit 6, (b) the frequency of the output of the sensing circuit 8, and (c) the amplitude of the output of the sensing circuit 8.

The circuit operates essentially as described with reference to Fig. 2. However, after the coin begins to leave the coil 10, the microprocessor 4 first measures the amplitude of the output of the sensing circuit 8, then measures its frequency, and then measures the amplitude again. The two amplitude measurements are averaged to obtain the blank amplitude value. The frequency measurement takes place over a sufficiently long time so that any slight fluctuations in the frequency do not affect the result.

Subsequently, the amplitude measurements are taken repeatedly. When a coin enters the space between coils 14 and 14', the amplitude begins to decrease. Successive amplitude measurements are compared and when the amplitude stops decreasing, a frequency measurement is taken. Subsequently, a series of further amplitude measurements are taken and when they indicate that the coin is just leaving coils 14, 14', a number of these measurements (preferably excluding the most recent measurements) are averaged to obtain the peak amplitude value.

This operation gives rise to three measurements, each comprising the ratio of a blank value to the peak value, which are compared with respective ranges to determine determine whether the coin is valid and, if so, to determine the coin value of the coin.

If the coin is valid, an ACCEPT signal is output to the output terminal 07 and the coin value of the coin is indicated by signals on lines 08 and 09.

The microprocessor 4 also time-divides the interval between the coin arriving at the coil 10 and when it leaves the coils 14, 14'. If this interval is less than a certain value, then this is an indication of a coin moving too fast for accurate measurement and the coin is therefore rejected. The microprocessor also checks the successive frequency values of the sensing circuit 6 and successive amplitude values of the sensing circuit 8 and if any of these change too quickly, the coin is rejected on the basis that it is either moving too fast or in an unstable manner.

When an operator wishes to test the operation of the validator, he operates a switch or connects a connection to provide a pulse to an interrupt terminal INT of the microprocessor 4 (instead of using a test terminal T1 as in Fig. 2). This causes the microprocessor to perform an interrupt routine which results in signals being produced on a serial data output line 010 in response to a coin passing through the coils 10, 14, 14'. The operator inserts a coin with known characteristics, such as a coin of a particular denomination selected to have substantially exactly average characteristics. The microprocessor compares the three measurements produced by this coin with specific ranges, which are narrower than those normally used for that denomination of coin, and as a result the data on output line 010 indicates what adjustments must be made to sensing circuits 6 and 8.

The operator has a test device that is connected to receive the data from output port 010 and the count pulses from output port 011. The device includes a logic circuit that decodes the data to provide an indication that indicates whether and how any of the components 61 (Fig. 3), 102 and 104 (Fig. 4) require adjustment.

The switches 150, 154 and 164 of Figure 5 may simply be logic gates, such as NAND gates.

Referring now to Figures 6A and 6B in conjunction with Figure 1, a preferred form of coil 10 will now be described. The coil is formed by a printed circuit etched on both sides of a two-sided printed circuit board 80. Figure 6A shows the side 82 of the board 80 which, in use, is in closer proximity to the coin path and Figure 6B shows the opposite side 84. The board 82 is placed in a plane parallel to the side walls of the channel 7.

On each side, the printed circuit board has been etched to form a spiral conductive pattern, with an overall essentially circular configuration.

Referring now to Fig. 6A, side 82 carries two terminal portions 86 and 88. The conductive path starts from terminal portion 86 and then spirals inward to an inner contact portion 94.

The terminal sections 86 and 88 are located directly opposite corresponding terminal sections on side 84, designated 86' and 88' respectively, and may, if desired, be connected thereby by appropriately plated through-holes. The inner contact section 94 is connected by a plated through-hole to a corresponding contact section 94' on side 84. From here the printed circuit pattern spirals outward to the terminal section 88'.

Thus, the terminal portions 86 and 88' form the opposite ends of the coil 10. In use, the field generated by the portion of the coil 10 on side 82 will extend in the same direction as the field generated by the part of the coil on side 84.

The respective parts of the coil 10 on the opposite sides of the plate 80 can be positioned very precisely with respect to the coin path so that there is good consistency in the measurements made by the coil 10 from one validator to another. Thus, only minor adjustments are required using the variable resistor 61 of Fig. 3.

The lower edge of the coil 10 is located at the bottom of the coin path or preferably slightly below it so that when a coin passing through the coil 10 attempts to jump, it has little or no effect on the coil area covered by the coin and hence on the measured value.

The term "coin" has been used here to cover not only genuine coins, but also non-genuine coins or other objects that can be picked up by the device for detecting validity.

Claims (26)

1. A coin validation device for determining whether an object is a genuine coin, the validation device comprising a sensing device (8, 14; 8, 14, 14') comprising a coin test sensor (14; 14, 14') and a validation circuit (4) coupled to an output (16) of the sensing device (8, 14; 8, 14, 14') for calculating a coin measurement based on the sum of values indicative of successive amplitudes of an output signal from the sensing device (8, 14; 8, 14, 14') generated when the object moves relative to the sensor (14; 14, 14') and for determining whether the measurement of a genuine coin is appropriate. is, characterized in that the measurement is made on the basis of the sum of values representing successive amplitudes of said output signal generated while the object is substantially in a position in which a peak level of the output signal amplitude occurs, the measurement being representative of the peak level. 2. A validity detecting device according to claim 1, wherein the validity detecting circuit (4) is operable to derive values indicative of successive attenuations of the output signal produced by the sensor (14; 14, 14') as said object moves relative to said sensor (14; 14, 14'), and to perform said calculation (when successive values change in such a way that the attenuation is said to be decreasing) on the basis of the sum of the first n of a larger number of values derived from said circuit (4). 3. A validation device according to claim 1, wherein the validation circuit (4) is responsive to derived values indicative of successive amplitudes of the output signal produced by said sensor (14; 14, 14') as said object moves relative to said sensor, to detect when a coin leaves the sensor (14; 14, 14') and to select the values on which the measurement is based in dependence thereon. 4. A device for detecting validity according to claim 2, wherein the circuit (4) for detecting validity is responsive to the derived values to detect when a coin leaves the sensor (14; 14, 14') and to select, in dependence thereon, those values on which the measurement is based. 5. A validation device according to claim 2 or claim 4, wherein said validation circuit (4) is arranged to read and store a predetermined number of values and to perform said calculation on the basis of the first n of these values, where n is less than the predetermined number. 6. A validation device according to any preceding claim, wherein the sensor is an inductive coin test sensor (14, 14') and the validation circuit is arranged to determine whether both amplitude and frequency changes produced by a coin in the vicinity of the sensor (14, 14') are representative of a valid coin. 7. A validity detecting device according to claim 6, wherein the validity detecting circuit (4) comprises means for alternately measuring the frequency and the amplitude of the output of the sensor. 8. A validity detecting device according to claim 6 or claim 7, wherein the validity detecting circuit (4) comprises means responsive to changes in the amplitude of the output of the sensor (14, 14') for determining when the frequency is to be sensed. 9. A validity detection device according to any one of claims 6 to 8, comprising a counter to provide an indication of changes in the output of said sensor (14, 14'). 10. A validity detection device according to claim 9, wherein the counter is used to count pulses from the sensor (14, 14') to provide an indication of their frequency and forms part of an analogue to digital converter to determine the amplitude of the output of said sensor (14, 14'). 11. A validation device according to any preceding claim, further comprising an arrival sensor (6, 10) for energizing at least part of the circuitry of the validation device in response to sensing the arrival of a coin at a sensing station of the validation device. 12. A device for detecting validity according to claim 11, comprising a processor (4) having a first state in which it performs processing operations and operates at a relatively high power level, and a second state in which it operates at a relatively low power level, and means (24) for periodically causing the processor to enter the first state to determine whether a coin has arrived using said arrival sensor (6, 10). 13. A validation device according to claim 12, wherein the processor (4) is arranged to perform, in its first state, a validation check operation in dependence on the arrival of a coin when sensed by the arrival sensor (6, 10). 14. A validation device according to claim 12 or 13, wherein the arrival sensor (6, 10) is an oscillator having an inductor (10), the frequency of the oscillator (6, 10) depends on the value of the inductor (10) and the validation device further comprises means responsive to a change in the frequency of the oscillator (6, 10) caused by a coin coming into proximity of the inductor (10) to provide a signal indicating the arrival of the coin. 15. A validation device according to claim 14, wherein the inductor (10) is coupled to an amplifier to generate the oscillator (6, 10), wherein at least a substantial part of the load of the amplifier (6) is independent of the presence of the coin. 16. A validation device according to claim 14 or 15, wherein the validation device is operable to determine whether the altered frequency caused by the proximity of the coin to the induction member (10) indicates that the coin is genuine. 17. Device for detecting validity according to claim 16, wherein the changed frequency of the oscillator (6, 10) predominantly provides information about the diameter of the coin. 18. A validity detection device according to claim 17, wherein the induction member (10) of the oscillator (6, 10) 10 comprises a coil having a height substantially equal to its width. 19. A validation device according to any one of claims 16 to 18, wherein the oscillator (6, 10) is arranged to apply a current to the inductor (10) for changes in the frequency of the oscillator (6, 10) caused by the proximity of the coin to be sensed to cause said energization, and wherein the changed frequency used in determining whether or not the coin is genuine is detected without applying the increased current. 20. A validation device according to any one of claims 15 to 19, comprising a counting device (24) coupled to the output of the oscillator (6, 10) to provide an indication of the frequency of the oscillator (6, 10). 21. A validity detection device according to claim 20, wherein the counting means (24) is also arranged to periodically cause the processor to enter its first state. 22. A device for detecting validity according to any one of claims 12 to 19, wherein the means (24) for causing the processor (4) to periodically enter the first state, comprising a counting device (24) operable to perform a count in response to an output of the arrival sensor (6, 10) and to cause the processor (4) to enter the first state when a predetermined count value is reached. 23. A validity detection device according to claim 20, 21 or 22, wherein the counting means (24) is operable while the processor (4) is in its first state to repeatedly perform a count and cause the processor (4) to be reset upon reaching a predetermined count value, the processor (4) being programmed to clear the counter before the predetermined count value is reached. 24. A validation device according to any preceding claim, comprising means (4) responsive to a value indicative of the speed at which a coin passes through a sensing station for providing a signal indicative of the coin being unacceptable in response to a determination that the coin has passed through the sensing station too quickly. 25. A device for detecting validity according to claim 24, wherein the signal-providing device (4) is operable in dependence on a value which provides information about the total transit time through the sensing station. 26. A device for detecting validity according to claim 24 or 25, wherein the signal-providing device (4) is operable in dependence on a value which is indicative of the rate of change of a signal which is generated in response to a coin coming close to a coin validation sensor (14, 14').