Coin acceptance mechanism and method of determining an acceptable coin

A coin acceptance mechanism and a method of determining an acceptable coin includes a pair of spaced apart coils between which a coin is passed. A signal is generated in one of the coils and induced in the other coil when a coin passes between the coils. The peak amplitude of the signal induced in the other coil and the peak phase difference between the signals in the pair of coils are both compared to a range of acceptable values stored in a memory to determine if a coin is acceptable and to assign a value to the coin deemed acceptable. The coin acceptance mechanism has a program mode in which it can be programmed to recognize coins of various values and coins or tokens from various countries.

DESCRIPTION--TECHNICAL FIELD 
The present invention relates to a coin acceptance mechanism and a method 
of determining whether a coin is acceptable and more particularly to a 
method and coin acceptance mechanism which utilizes a pair of spaced apart 
coils and wherein a signal is established in one of the coils and induced 
in the other of the coils which signal changes in phase and amplitude when 
a coin passes between the pair of spaced apart coils. 
BACKGROUND OF THE INTENTION AND REFERENCE TO RELATED PATENTS 
Some known coin acceptance mechanisms include means for sensing the phase 
change of a signal established in a first coil and induced in a second 
spaced apart coil when a coin passes between the pair of coils. Others 
include means for sensing the change in amplitude of a signal established 
in a first coil and induced in a second coil when a coin passes between 
the pair of coils. Examples of such devices are disclosed in U.S. Pat. No. 
4,998,610, U.S. Pat. No. 5,056,644, and U.S. Pat. No. 5,097,934. 
It is desirable to be able to readily change the criteria for determining 
an acceptable coin to enable the coin acceptance mechanism to work with 
coins of various national governments and coins or tokens of various 
denominations. The size and metallurgical content of Canadian coins 
differs from that of United States coins and differs from that of 
Australian coins. Hence, it is desirable to have a coin mechanism in which 
the criteria for determining whether a coin or token is acceptable can be 
varied to accommodate coins of various nationalities, values, size and 
metallurgical content. 
The present invention overcomes the disadvantages associated with the prior 
art by providing a coin acceptance mechanism which can be programmed to 
determine a range of acceptable values for criteria associated with 
acceptable coins of various nationalities and values. 
SUMMARY OF THE INVENTION 
The present invention provides a new and improved coin acceptance mechanism 
which includes a coin receiving chute having a pair of sides between which 
coins are adapted to pass, first and second spaced apart coils located on 
opposite sides of the coin chute and a signal generator for generating a 
first electrical signal and directing the first signal to the first coil. 
The first coil induces a second signal in the second coil which changes in 
phase and amplitude when a coin passes between the first and second coils. 
The coin acceptance mechanism includes means for determining the phase 
difference between the first and second signals when a coin passes between 
the first and second coils and establishing a third signal indicative of 
the phase difference, means for determining the peak amplitude of the 
second signal when a coin passes between the first and second coils and 
generating a fourth signal indicative of the peak amplitude of the second 
signal, memory means for storing a range of acceptable values for the peak 
phase difference between the first and second signals and the peak 
amplitude of the second signal which are indicative of an acceptable coin, 
and microprocessor means for receiving the third signal and fourth signal 
determining the peak phase difference between said first and second 
signals and the peak amplitude of the second signal. The microprocessor is 
connected to the memory means for comparing the third and fourth signals 
with the range of acceptable values in the memory means to determine 
whether a coin passing between the coils is an acceptable coin and for 
assigning a credit value for coins which are determined to be acceptable. 
The microprocessor has a learning mode in which a plurality of sample 
acceptable coins of a single value are sequentially placed in the coin 
chute and the third and fourth signals generated by the plurality of 
sample acceptable coins are averaged to determine an acceptable range of 
values for each of the third and fourth signals which represent an 
acceptable coin of the single value. The microprocessor stores the 
determined acceptable range of values in the memory means. 
A further provision of the present invention is to provide a new and 
improved method of determining whether a coin which passes between a pair 
of coils in a coin acceptance mechanism is an acceptable coin and 
assigning an acceptable range of values to coins deemed acceptable 
including the steps of: providing a pair of spaced apart coils through 
which coins must pass, establishing a first electrical signal in one of 
the coils which induces a second signal in the other of the coils, passing 
a plurality of sample acceptable coins of a first value between the pair 
of coils, determining the phase difference between the first electrical 
signal and the second electrical signal when each of the plurality of 
sample acceptable coins passes between the pair of coils, determining the 
peak amplitude of the second electrical signal when each of the plurality 
of sample acceptable coins passes between the pair of coils, determining 
the average peak phase difference between the first and second electrical 
signals and the average peak amplitude of the second electrical signal for 
the plurality of acceptable sample coins, using the determined average 
peak phase difference and the determined average peak amplitude to 
determine a range of acceptable values for the peak phase difference 
between the first and second signals and the peak amplitude of the second 
signal when acceptable coins of the first value are passed between the 
pair of spaced apart coils, passing a coin between the coils, determining 
the peak phase difference between the first and second signals when the 
coin passes between the pair of coils, determining the peak amplitude of 
the second signal when the coin passes between the pair of coils, and 
comparing the determined peak phase difference between the first and 
second signals and the determined peak amplitude of the second signal with 
the range of acceptable values to determine if the coin passing between 
the pair of coils is an acceptable coin and for assigning a value to a 
coin deemed acceptable.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the Figures, and more particularly to FIGS. 1 and 2, a coin 
acceptance mechanism 10 is illustrated. The coin acceptance mechanism 10 
is associated with a coin chute 12 having pair of side walls 14, 16 
between which a coin 18 is adapted to pass. A pair of spaced apart coils 
20, 22 are mounted on the side walls 14, 16 of the coin chute with the 
coil 20 disposed on side wall 16 and the coil 22 disposed on side wall 14. 
The coils 20, 22 are disposed on the side walls 14, 16 of the coin chute 
12 so that any coin passing through the coin chute 12 must pass between 
the spaced apart coils 20, 22. It should be realized that although the 
coils 20,22 are described as being mounted "on" side walls 14, 16, the 
coils could be mounted in or behind side walls 14, 16 depending on the 
construction of side walls 14, 16. The coils 20, 22 are energized by the 
coin acceptance mechanism 10 as will be discussed more fully hereinafter. 
A solenoid 24 is connected to an output 38 of the coin acceptance mechanism 
10 and is adapted to be energized to direct coins passing through the coin 
chute 12 to a coin box 28 or a coin return chute 30. An arm or door 26 is 
connected to the solenoid 24 to direct coins which are deemed acceptable 
to the coin box 28 and coins which are deemed unacceptable to the coin 
return chute 30. When solenoid 24 is energized door 26 is moved to its 
phantom line position, illustrated in FIG. 1, and coins passing through 
coin chute 12 drop into coin box 28. When solenoid 24 is not energized the 
door 26 is "closed" and coins in chute 12 pass to the coin return chute 
30. A sensor 32 is connected to the coin acceptance mechanism 10 for 
establishing a coin received signal when an acceptable coin passes from 
the coin chute 12 into the coin box 28. The coin acceptance mechanism 10 
is adapted to direct a signal to a vending apparatus 34 when an acceptable 
coin activates sensor 32 and passes into the coin box 28. The coin 
acceptance mechanism 10 establishes the signal to the vending apparatus 34 
which is indicative of the value of the acceptable coin which passes into 
the coin box 28. The vending apparatus 34 can be one of several known 
vending apparatus for vending bottles, fluid or snacks. In the preferred 
embodiment, the vending apparatus 34 is a manually operated car wash and 
the vending apparatus 34 controls the wash time or items to be dispensed. 
The coin acceptance mechanism 10, more fully illustrated in FIG. 3, 
includes a signal generator 46 which generates a first electrical signal 
which is directed along conductor 40 to the coil 20. The first signal in 
coil 20 induces a second signal in coil 22 which is spaced apart from coil 
20 in a well-known manner. When a coin passes between coils 20 and 22, the 
second signal induced in coil 22 by the first signal in coil 20, changes 
in both phase and amplitude dependent upon the size of the coin 18 and the 
metallurgical content of the coin. The coin acceptance mechanism 10 
utilizes the sensed phase difference between the signals in coils 20 and 
22 and the amplitude of the signal induced in coil 22 to determine whether 
a coin which passes between the coils 20, 22 is an acceptable or 
unacceptable coin. 
The coin acceptance mechanism 10 includes a microprocessor 50 and a 
non-volatile memory 52 which is connected to the microprocessor 50. The 
memory 52 includes information stored therein which is indicative of 
ranges of acceptable values for the peak phase difference between the 
signal in the coil 20 and the signal in coil 22 and acceptable ranges for 
the peak amplitude of the second signal induced in coil 22 when an 
acceptable coin passes between the coils 20 and 22. 
The output of coil 22 is directed along line 42 through a rectifier 54 and 
filter circuit 55 to the analog input 56 of the microprocessor 50. The 
input on line 56 to microprocessor 50 is a fourth signal which is an 
analog voltage indicative of the amplitude of the second electrical signal 
induced in coil 22 when a coin passes between the spaced apart coils 20, 
22. The microprocessor 50 receives the fourth signal and determines the 
peak amplitude of the second electrical signal. The output of coil 22 is 
also directed along line 42 to an input 41 of phase difference circuit 60. 
An output from the first coil 20 is directed along line 40 to an analog 
input 43 of the phase difference circuit 60. The phase difference circuit 
60 is operable to direct a third signal through a filter circuit 140 to 
the input 62 of the microprocessor 50 which is an analog voltage 
indicative of the phase difference between the signals in coil 20 and coil 
22 when a coin passes between the coils. The microprocessor 50 receives 
the third signal and determines the peak phase difference between the 
signals in coils 20 and 22. 
When a coin passes between coils 20, 22, the microprocessor 50 receives the 
fourth signal on analog input 56 which is indicative of the peak amplitude 
of the second signal in coil 22 and the third signal at input 62 which is 
indicative of the phase difference between the first and second signals in 
coils 20 and 22 when a coin passes between the coils 20 and 22. The 
microprocessor 50 determines the peak phase difference between the first 
and second signals and the peak amplitude of the second signal and 
compares the signals on lines 56 and 62 with the information stored in the 
memory means 52 to determine if the coin passing between the coils 20 and 
22 is an acceptable coin or an unacceptable coin. If a coin is deemed an 
acceptable coin, i.e., the peak phase difference between the first and 
second signals and the peak amplitude of the second signal are both within 
the range of acceptable values in memory means 52, the microprocessor 50 
energizes solenoid 24 to move arm 26 into its phantom line position 
illustrated in FIG. 1 to direct the acceptable coin passing through the 
coin chute 12 to the coin box 28. If a coin is not acceptable, the 
solenoid 24 is not energized and the arm 26 remains in its full line 
position illustrated in FIG. 1 in which coins are directed to the coin 
return chute 30. If a coin is deemed acceptable and is directed to the 
coin box 28, the coin passes sensor 32 which establishes a signal on the 
input 64 of the microprocessor 50. Upon receipt of the signal at input 64 
from sensor 32, the microprocessor 50 establishes a credit output on line 
66 to a vending apparatus 34 indicative of receipt of an acceptable coin 
and the value of the acceptable coin. 
The range of acceptable values stored in the non-volatile memory 52 can 
preferably be a plurality of ranges of acceptable values wherein each 
range is indicative of an acceptable range for a coin of a predetermined 
value. For example, if quarters are directed through the coin chute 12, 
the acceptable ranges for the peak amplitude of the induced second signal 
in coil 22 and the peak phase difference between the first and second 
signals in coils 20 and 22 will be a first set of acceptable ranges. If 
the acceptable coin is a dime, the acceptable ranges stored in memory 52 
will include a second acceptable range of the peak amplitude of the second 
signal induced in coil 22 and a second acceptable range for the peak phase 
difference between the first and second signals in coil 20 and coil 22. 
The peak amplitude of the second signal induced in coil 22 and the peak 
phase difference between the signals in coils 20 and 22 is sufficiently 
different for coins of different values due to the size and metal content 
of the various coins so that accurate distinct acceptable ranges can be 
set in the memory means 52. 
The coin acceptance mechanism 10 includes a learning mode wherein sample 
acceptable coins of a single first predetermined value are sequentially 
placed in the coin chute 12 and the peak amplitude of the second signal 
induced in coil 22 and the peak phase difference between the signals in 
coils 20 and 22 is recorded for each of the sample acceptable coins of a 
predetermined value by the microprocessor 50. The microprocessor 50 then 
calculates the average peak amplitude for the second signal induced in 
coil 22 and the average peak phase difference between the signals in coils 
20 and 22 for the signals generated when the sample acceptable coins of a 
single first value are passed through the coin acceptance mechanism 10. 
The average value of the peak amplitude of the second signal induced in 
coil 22 and the average value of the peak phase difference between the 
signals in coil 20 and 22 for the sample acceptable coins is then utilized 
to establish in the microprocessor 50 a range of acceptable values for the 
peak amplitude and peak phase difference associated with acceptable coins. 
The range of calculated acceptable values for the amplitude and phase 
difference is then stored by the microprocessor 50 in the memory 52. 
The range of acceptable values can be calculated by the microprocessor 50 
using two methods. In the first method, the microprocessor takes the 
average value of the peak amplitude of the second signal at coil 22 and 
the average value of the peak phase difference between the signals in coil 
20 and 22 and adds a fixed predetermined plus and minus value to each of 
the determined average values to determine a range of acceptable values 
for the peak amplitude and peak phase difference of an acceptable coin. In 
the second method, the microprocessor 50 determines an acceptable 
percentage deviation, plus or minus, from the determined average value of 
the peak amplitude of the signal in coil 22 and the peak phase difference 
between the signals in coil 20 and 22 to determine a range of acceptable 
values for the peak amplitude and peak phase difference associated with 
acceptable coins of a predetermined value. 
It should be appreciated that the microprocessor 50 can set a plurality of 
ranges of acceptable values which are indicative of the acceptable ranges 
for the signals of a plurality of acceptable coins having different 
values. For example, a first range of values can be stored in memory 52 
indicative of the acceptable range of the peak amplitude determined at 
coil 22 for the second signal and the peak phase difference sensed between 
coils 20 and 22 which is indicative of the acceptable range of values for 
quarters, and a second range of acceptable ranges could be stored in 
memory 52 which is indicative of an acceptable coin of a different value, 
for example, a dime, passing between coils 20 and 22. 
Referring more particularly to FIGS. 4a and b, the circuitry of the coin 
acceptance mechanism 10 is illustrated in more detail. The signal 
generator 46, includes an L.C. oscillator formed by transistors 72, 74, 
amplifier 76, inductor 90 and capacitors 88 and 89 which establishes an 
output on line 80 which is directed through an amplifier 92 to the coil 20 
to establish the first signal in coil 20. Capacitor 82 is connected across 
coil 20 and capacitor 84 is connected across coil 22. The capacitors 82,84 
establish a resonant circuit with coils 20,22 to provide a clean 
sinusoidal signal across both coils 20,22. Coil 20 induces the second 
electrical signal in coil 22 which is directed along line 42 to the 
rectifier circuit 54 which includes amplifiers 98 and 104 and their 
associated electrical components. The output of coil 20 is normally 
quiescent, i.e. a sinusoidal wave having a relatively small amplitude is 
established in coil 22, but when a coin 18 passes between coils 20,22 an 
increase in the sinusoidal amplitude, schematically illustrated at 42a, is 
established in coil 22 which is sensed by the coin acceptance mechanism. 
The peak value of the amplitude at the output of coil 22 is recorded and 
the phase difference between the sinusoidal signals in coils 20 and 22 is 
sensed. Line 42 is connected to the input of an amplifier 96 whose output 
is directed through a rectifier circuit 54 including amplifier 98, diode 
100 and resister 102 which are connected to the input of amplifier 104. 
The rectifier circuit 54 rectifies the output of the coil 22 and 
establishes the rectified wave form schematically illustrated at 104a, at 
the output of the amplifier 104. Amplifier 104 directs the rectified 
signal through filter circuitry 103 including amplifier 106, capacitors 
108 and 109 and resisters 110 and 111, along line 112 to another amplifier 
circuit 55 which includes amplifier 114, resisters 116 and 118 and 
capacitor 120. The output from the amplifier 114, schematically 
illustrated at 114a, is a pulse which represents the envelope of the 
rectified sinusoidal signal established in coil 22 by the passage of the 
coin between coils 20,22. The pulse is directed to the analog input 56 of 
microprocessor 50 and is an analog signal indicative of the amplitude of 
the envelope of the second signal induced in coil 22 when a coin of a 
predetermined value passes between coils 20 and 22. Microprocessor 50 
records the peak value of the pulse at analog input 56. 
The phase difference circuit 60 includes a pair of comparators 126 and 128 
whose outputs are summed at 129 and directed through gates 130, 132, 
connected as inverters, to buffer the output signal. The comparator 126 
has an input 43 connected via line 144 to line 40 which is connected to 
the first coil 20 and establishes a signal which is indicative of the 
signal in the coil 20 at the input to comparator 126. An input 41 to the 
comparator 128 is connected via line 146 to line 42 which is connected to 
coil 22 and establishes a signal which is indicative of the signal in coil 
22 at the input of comparator 128. The outputs of the comparators 126 and 
128 are connected together at 129 and establish a rectangular pulse having 
a width or duration which is representative of the phase difference 
between the signal in coil 20 and the signal induced in coil 22. The 
output of comparators 126,128 are directed through buffer gates 130 and 
132 to a filter circuit including capacitors 136 and 138 and an amplifier 
134. The output of amplifier 134 is connected through a filter circuit 140 
including amplifier 142, capacitors 144 and 145 and resistors 146 and 147 
to the analog input 62 of the microprocessor 50. The input at terminal 62 
is the third signal which is an analog signal indicative of the phase 
difference between the first signal in coil 20 and the second signal 
induced in coil 22. 
The sensor 32 in the preferred embodiment as is illustrated in FIG. 4a, 
includes a light-emitting diode 150 which is coupled to a photo-receptive 
transistor 152. The sensor 132 is located in a position in which a coin 18 
which passes into coin box 28 will pass between the light-emitting diode 
150 and the photo-receptive transistor 152, breaking the stream of 
radiation in a well-known manner and initiating an output signal from the 
photo-transistor 152 which is directed to an amplifier 154. The output of 
amplifier 154 is directed to the digital input terminal 64 of 
microprocessor 50. Sensor 32 is thus operable to establish a signal at the 
input 64 of microprocessor 50 which indicates receipt of a coin from the 
coin chute 12 to the coin box 28. Sensor 32 prevents tampering and insures 
that a coin is received in the coin box 28. 
When a coin 18 is received in the coin chute 12, it passes between coils 20 
and 22 and the amplitude of the second signal induced in coil 22 is sensed 
and a fourth signal is established at the analog input 56 of the 
microprocessor 50 indicative of the peak amplitude of the second signal 
induced in coil 22. The phase of the signals in coil 20 and coil 22 are 
compared in the phase difference circuit 60 and a third signal indicative 
of the phase difference between the signal in coil 20 and the signal in 
coil 22 is established at analog input 62 of the microprocessor 50. The 
microprocessor 50 then compares the peak of the fourth signal at input 56 
and the peak of the third signal at input 62 with the range of acceptable 
values stored in memory 52 which preferably is a non-volatile memory. If 
the fourth signal at input 56, indicative of the peak amplitude of the 
second signal in coil 22, and the signal at input 62, indicative of the 
peak phase difference, are both within the acceptable range within memory 
52, the microprocessor 50 will determine that the coin passing between the 
coils 20 and 22 is an acceptable coin and the solenoid 24 will be 
momentarily energized by microprocessor 50 to move arm 26 to its phantom 
line position illustrated in FIG. 1 to direct the coin deemed acceptable 
to the coin box 28. When the coin passes sensor 32 on its way to the coin 
box 28, sensor 32 will signal microprocessor 50 at digital input 64 and 
the microprocessor will establish a credit output on terminal 66. 
Preferably the credit output can be in the form of a series of pulses 
which are indicative of the value of the coin which has been deemed 
acceptable and passed to the coin box 28. For example, if a quarter is 
sensed, five pulses can be generated and if a dime is sensed two pulses 
can be generated. However, other types of coded signals could be generated 
and still come within the scope of the present invention. 
The microprocessor 50 can be programmed to program memory 52 with a 
plurality of acceptable ranges for the amplitude of the signal in coil 22 
and the phase difference between the signals in coil 20 and 22 when coins 
of an acceptable value are received in the coin chute 12. To program the 
microprocessor a button 156 is pushed to put the microprocessor 50 in its 
program mode. A LED 158 lights to indicate the microprocessor 50 is in its 
program mode. The operator then sequentially feeds 15 sample acceptable 
coins of a single value one by one through the coin chute 12 and the 
microprocessor 50 measures and records the phase difference and peak 
amplitude of each of signals generated by the sample coins. After 15 coins 
are dropped into the chute 12 the programming is complete, LED 158 turns 
off, and the microprocessor determines the average peak amplitude value 
and the average peak phase difference and establishes a range of 
acceptable values for the peak amplitude and peak phase difference which 
is stored in the memory 51. While the programming mode has been disclosed 
as using 15 sample coins, more or less sample coins could be used without 
departing from the scope of the present invention. 
When the microprocessor is placed in its program mode, a plurality of 
sample acceptable coins of a single value can be sequentially dropped into 
the coin chute 12 and sequentially pass between coils 20 and 22. As each 
sample acceptable coin passes between the coils 20 and 22, the peak 
amplitude of the second signal induced in coil 22 and the peak phase 
difference between the first and second signals in coils 20 and 22 are 
determined and stored in the microprocessor 50. The microprocessor 50 then 
averages the peak signals received from the sample acceptable coins to 
determine an average peak amplitude and an average peak phase difference 
value. The microprocessor then determines an acceptable range for the peak 
amplitude and the peak phase difference using the determined average peak 
amplitude and peak phase difference. The microprocessor 50 then downloads 
the determined acceptable range of values for the peak amplitude and peak 
phase difference into the memory 52. The program mode is repeated using a 
plurality of sample acceptable coins of a different value. In this manner, 
the coin acceptance mechanism 10 can be programmed to accept nickels, 
dimes, quarters, etc. in United States currency and coins or tokens of 
various denominations in other currencies such as Canadian coins, 
Australian coins, Mexican coins, etc. The coin acceptance mechanism 10 is 
operable to determine whether the coins which pass between coils 20 and 22 
are acceptable coins and to set a range of values for coins deemed 
acceptable. The microprocessor 50, when comparing the received peak 
amplitude and peak phase difference signals with the range of acceptable 
values stored in the memory 52, also determines which of the plurality of 
ranges stored in memory 52 in which the received signals fit to enable the 
microprocessor 50 to determine the value of a coin deemed acceptable. 
From the foregoing, it should be apparent that a new and improved coin 
acceptance mechanism 10 has been disclosed. The coin acceptance mechanism 
includes a coin receiving chute 12 having a pair of sides 14, 16 between 
which coins 18 are adapted to pass. First and second spaced apart coils 
20, 22 are located on opposite sides of the coin chute 12 in a location in 
which a coin 18 received in the chute 12 passes between the first and 
second spaced apart coils 20, 22. A signal generator 46 is provided for 
generating a first electrical signal and directing the first signal to the 
first coil 20. The first coil 20 induces a second signal in the second 
coil 22 which signal changes in phase and amplitude when a coin passes 
between the first and second coils 20, 22. A phase difference circuit 60 
is provided for measuring the phase difference between the first and 
second signals when a coin passes between the first and second coils 20, 
22 and generates a third signal at input 62 indicative of the phase 
difference. Means are provided for measuring the peak amplitude of the 
second signal induced in coil 22 and generating a fourth signal at 
terminal 56 which is indicative of the peak amplitude of the second 
signal. A memory 52 is provided having stored therein a range of 
acceptable values for the peak phase difference between the first and 
second signals and the amplitude of the second signal which are indicative 
of an acceptable coin passing between the first and second coils 20, 22. A 
microprocessor 50 is provided for receiving the third signal at input 62 
and the fourth signal at input 56 and connected to the memory means 52 for 
comparing the third and fourth signals with the range of acceptable values 
in the memory 52 to determined if a coin passing between the coils 20, 22 
is an acceptable coin and for assigning a credit value for coins which are 
deemed to be acceptable. The microprocessor 50 has a learning mode in 
which sample acceptable coins can be used to program the range of 
acceptable values in the memory means 52. 
In addition, a method has been disclosed for determining whether a coin 
which passes between a pair of coils 20, 22 in a coin acceptance mechanism 
10 is an acceptable coin and assigning a value to a coin which is deemed 
acceptable including the steps of: a) providing a pair of spaced apart 
coils 20, 22 between which coins 18 must pass when received in the coin 
acceptance mechanism 10; b) establishing a first electrical signal with 
signal generator 46 in coil 20 which induces a second electrical signal in 
coil 22 which second signal changes in phase and amplitude when a coin 
passes between the pair of spaced apart coils 20 and 22; c) sequentially 
passing a plurality of sample acceptable coins of a single value between 
the pair of coils 20, 22 in the coin acceptance mechanism 10; d) 
determining the phase difference with phase difference circuit 60 between 
the first electrical signal in coil 20 and the second electrical signal 
induced in coil 22 when each of the plurality of sample acceptable coins 
passes between the pair of coils 20, 22; e) determining the amplitude of 
the second electrical signal in the coil 22 when each of the plurality of 
sample acceptable coins passes between the pair of coils 20, 22; f) 
determining in the microprocessor 50 the average peak phase difference 
between the first and second electrical signals for the plurality of 
sample acceptable coins and the average peak amplitude of the second 
electrical signal for the plurality of sample acceptable coins; g) using 
in the microprocessor 50 the determined average peak phase difference to 
set in the memory means 52 a range of acceptable values for the peak phase 
difference between the first and second signals when acceptable coins of 
the single value are passed between the pair of spaced apart coils 20, 22; 
and h) using in the microprocessor 50 the determined average peak 
amplitude of the second electrical signal to set in the memory means 52 a 
range of acceptable values for the peak amplitude of the second electrical 
signal when acceptable coins of the single value are passed between the 
pair of spaced apart coils 20, 22. After the coin acceptance mechanism 10 
has been programmed, a coin can be passed between the pair of coils 20, 22 
and the phase difference between the first and second signals in the pair 
of coils 20,22 can be sensed along with the peak amplitude of the second 
signal to determine whether the coin is an acceptable coin.