Note: Descriptions are shown in the official language in which they were submitted.
1 336782
BACKGROUND OF THE INVENTION
1. Field of The Invention
The invention related to a low power apparatus for
detecting the validity and denomination of a coin.
2. Description of the Prior Art
There is believed to be a substantial need for low
power coin discriminators for use in devices such as parking
meters, telephones, and vending machines. Most prior art coin
discriminating apparatus tends to be mechanical in nature.
Only a few moderately reliable electronic devices are known.
Since most prior art electronic devices are located near a
source of power, the problem of power consumption has never
been a major concern. However, there are certain environments,
such as parking lots, where external power isn't available.
Therefore, it was necessary to search for a low power, highly
accurate and highly rugged unit. Since no prior art devices
cppeared to fit that description, it was necessary to invent
one that did.
The use of piezoelectric elements in the context of
coin discrimination is not common. However, U.S. Patent No.
3,776,338 does disclose a piezoelectric detector used for de-
tecting the presence of a coin. The use of a rudimentary strik-
ing pad to cover the surface of a piezoelectric element is
also discussed. Another discussion of the use of piezoelectric
elements is found in an article entitled "Poly(vinylidene)
Fluoride Used For Piezo Electric Coin Sensorsn. The article
was written by G. R. Crane of Bell Labs and appeared in Volume
SU 25, No. 6, (November 1978) of the IEEE Transactions on Sonics
and Ultrasonics at pages 393 - 395.
Some prior art references describe systems which
employ two or more steps to detect coins. For example, U.S.
Patent No. 4,082,099 discloses a two-step method for coin dis-
crimination. The first step is the detection of the coin by a
metal sensor. The second step employs photoelectric elements.
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Similarly, U.S. Patent No. 4,436,196 discloses another two-part
test and includes a discussion of the use of an LED and micro-
processor. Likewise, U.S. Patent No. 3,211,267 discloses a
dual test to determine the weight and diameter of the coin.
A number of prior art references discuss the use of
other photoelectric devices to detect the presence and/or areas
and/or diameters of coins. Note specifically that U.S. Patents
No. 3,978,962; 4,249,648; 4,267,916 and 4,474,281 disclose the
use of arrays of LED's to detect coin parameters such as veloc-
ity, area, diameter, etc. Other patents of interest with regard
to the photoelectric detection aspects of the present invention
are U.S. Patents 3,939,954; 4,436,103 and 4,442,850. Insofar
as understood, none of the prior art references cited above or
known to the inventor have the same structure or function as
the unique invention desc.ibed herein.
SUMMARY OF THE INVENTION
Briefly described, the invention is comprised of a
low power coin discrimination apparatus for use in parking
meters, telephones, vending machines and similar devices. The
coin discriminator includes a piezoelectric transducer for
measuring the mass of the coin and a photoelectric sensor for
sensing the area of the coin. The circuit begins in a low
power, dormant state. A coin is initially inserted into the
meter. Movement of a coin transfer handle activates a limit
switch which generates a wake-up pulse. The handle movement
also forces the coin to enter a chute causing it to fall on
the piezoelectric transducer. A cellular urethane pad covers
the piezoelectric element and serves to dampen oscillations
generated by the coin impact. If a large enough pulse is gen-
erated by the impact on the piezoelectric transducer, an infra-
red LED in the photoelectric sensor section of the circuit is
turned on by a controlling microprocessor. The photosensor
portion of the circuit preferably includes a photodiode illumi-
nated by the infrared LED. A microprocessor circuit digitally
_ ~ 3 ~ 1 336782
samples the output of the photodiode to determne the minimum
illumination (at the point of maximum eclipse) which in turn
represents the net area of the coin. Therefore the photosensor
can discriminate between invalid coins which have holds and
valid coins of the same diameter. The signal generated by the
coin impacting on the piezoelectric transducer is integrated
and then sampled by the microprocessor in order to determine
the mass of the coin. The microprocessor first uses the infor-
mation generated by the photoelectric sensor to determine if
the coin is within acceptable area limits. If it passes the
photosensor test, then the mass information from the piezo-
electric transducer is also compared to th corresponding limits
as a dual accuracy check. The discriminator a~tomatically
returns to a dormant state once it has completed the discrimi-
nation process. The invention is preferably used in a parking
meter, however, it could also be used in other contexts such
as telephones and vending machines.
These and other features of the inventicn will be
more fully understood by reference to the following drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a block diagram of the preferred embodi-
ment of the invention;
Figure 2 is a detailed schematic diagram of the pre-
ferred embodiment of the invention illustrated in Figure l;
Figure 3 is a cross-sectional view of the coin chute
showing the manner in which the coin impinges on the piezo-
electric transducer;
Figure 4A illustrates the photo optical system for
measuring the area of a coin;
Figure 4B illustrates the manner in which a coin
eclipses the optical system shown in Figure 4A
Figure 5A illustrates the waveforms of two different
signals produced when the different coins impinge on the piezo-
electric element;
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Figure 5B illustrates the integrals of the signals
shown in Figure 5A for two different coin denominations;
Figure 5C illustrates the signal output from the
photoelectric coin area detection system of Figures 4A and 4B
for two different coin denominations;
Figure 6A is a front elevational view of an assembled
parking meter embodying the present invention;
Figure 6B is a front elevational view of the parking
meter of Figure 6A with the hood of the meter removed;
Figure 6C is a left side elevational view of the
parking meter assembly shown in Figure 6B;
Figure 6D is a top plan view of the parking meter
assembly shown in Figure 6B;
Figure 6E is a side elevational view of one of the
track plates that define the coin chute;
Figure 6F is a perspective view of the coin entrance
transfer block;
Figure 6G is a perspective view of the coin entrance
frame piece;
Figure 6H is a front elevational view of the LCD
flat assembly;
Figure 6I is a side elevational view of the LCD flag
assembly of Figure 6H;
Figure 6J is an exploded view of the coin transfer
box and lever combination;
Figure 6K is an exploded view showing how the parking
meter housing receives the interchangeable electronic modules;
Figure 7A illustrates the invention in the context
of a telephone; and,
Figure 7B illustrates the invention in the context
of a vending machine.
DETAILED DESCRIPTION OF THE INVENTION
During the course of this description like numbers
will be used to identify like elements according to the different
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views and figures which illustrate the invention.
The preferred embodiment of the invention 10 is illus-
trated in Figure 1 in block diagram form and in structural
form in Figures 3-6R. Initialy the circuit 10 is in a dormant
low power state. A user starts the meter by inserting a coin
12 into slot 81 and then moving handle 98 to the right causing
the coin transfer block 96 to impinge upon and activate limit-
type wake-up switch 44. Simultaneously the coin 12 is moved
by housing 102 to the edge of base 114 of coin entrance frame
piece 80 causing it to fall down chute 52. Wake-up switch 44
causes the circuit to enter a low power, pre-active state for
a maximum of about 500 milliseconds. During the 500 millisecond
preactive period, the microprocessor is preconditioned to look
for a signal from the piezo transducer 16. Also the 32.768kHz
internal clock 33 controlled by crystal 34 is automatically
disconnected and replaced by a faster but less accurate 400kHz
clock 35. The clock rate of the 400kHz clock is established
by the resistance/capacitance network 40 and 42 which corresponds
to resistors Rll and C4 in Figure 2. The impact of coin 12 on
piezoelectric element 14 causes the LED D4 of drive circuit 26
to turn on in advance of coin 12. If no coin impacts on piezo-
electric transducer 14 within 500 milliseconds, then the circuit
automatically turns off. The output of piezoelectric transducer
14 is integrated by amplifier and integrator circuit 16 and
fed as an output to analog-to-digital converter 18. The output
of analog-to-digital converter 18 is fed to microprocessor 20.
LED circuit 26 illuminates photosensor 28 which produces an
output that is amplified by amplifier circuit 30 and fed as a
second input to the analog-to-digital converter circuit 18.
Activation of the piezoelectric transducer 14 produces an enable
signal to voltage regulator 22 which causes the voltage VcB to
jump from a low voltage VB to a higher voltage Vc (5 volts)
which is sufficient to drive LED D4. Regulator 22 also provides
a "low battery" signal back to microprocessor 20 to indicate
if the power source is running low.
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The coin chute 52 is constructed so that the coin 12
will pass between LED circuit 26 and photosensor 28 after it
has impacted upon piezoelectric transducer 14. Microcomputer
20 samples the output from analog-to-digital converter 18 at
very short intervals to determine when a coin 12 has achieved
a maximum eclipse of the iight between LED circuit 26 and photo-
sensor circuit 28.
A coin identification and time programming memory
circuit 32 is programmed to assist microprocessor 20 in the
identification of a coin 12 of unknown denomination. The out-
put from microprocessor 20 acts as an input to LCD driver cir-
cuit 36 which in turn drives the LCD and flags of circuit 38.
The circuit 10 may be inltialized by he manual operation of
clear time switch 46.
Figure 2 is a detailed schematic diagram of the pre-
ferred embodiment of the invention illustrating all of the
important specific details of the circuitry. References also
should be made to the following parts list which further identi-
fies the values and origin of the electrical components:
PARTS LIST
A. INTEGRATED CIRCUITS
Item No. Part No. Manufacturer Description
Ul TLC27M4AIM Texas Instruments Operational Amp
U2 TLC541IN Texas Instruments A/D Converter
U3 X2443PI Xicor NOVRAM
U4 COP324CN National Semicon- Microprocessor
ductor
U7 MM5483N National Semicon- LCD Driver
ductor
U9 RV4193NB Raytheon Regulator
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B. CAPACITORS
Item No. Description
Cl 100pf Polystyrene + 2.5%
C2 . luf Mono CD Bypass
C3 100pf DM Mica 5%
C4 .047uf Poly + 5%
C5 . luf Mono CD Bypass
C6 82pf DM Mica 5%
C7 470pf DM Mica 5%
C8 50pf DM Mica 5%
C9 50pf DM Mica 5%
C10 470uf, 6.3V Electrolytic
Cll 56pf DM Mica 5% .
C . RES I STORS
Item No. Description
Rl 2.4M 5% 1/4W Carbon
R2 10K 5% 1/4W Carbon
R3 20M 5% 1/4W Carbon
R4 10M 5% 1/4W Carbon
R5 10R 1% RN55D Type MF
R6 40R 1% RM55D Type ~,F
R7 lM 5% 1/4W Carbon
R8 180, 5% 1/4W Carbon
R9 4.7R 5% 1/4W Carbon
R10 4.7R 5% 1/4W Carbon
Rll lM 5% 1/4W Carbon
R12 15R 5% 1/4W Carbon
R13 lM 5% 1/4W Carbon
R14 220R 5% 1/4W Carbon
R15 20M 5% 1/4W Carbon
R16 4.7K 5% 1/4W Carbon
R17 360R 5% 1/4W Carbon
R18 51. lR 1% RN55D Type MF
Rl9 16.9R 1% RN55D Type MF
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D. MISCELLANEOUS
Item No. Part No. Description
L1 300MH Inductor, 1/4W style, molded
CR1 CXIV-32.768kHz Satek Inc., 32.768kHz, crystal
D1 IN914(lN4148) Diode
D2 HSCH 1001 Diode
D3 HSCH 1001 Diode
D4 LD242-2 LED, Siemens
D5 SFH206 Photodiode, Siemens
Q1 2N3906 Transistor
Q2 2N3906 Transistor
Q3 2N4401 Transistor
X1 16500-5A Piezo Electric Ceramic Disc,
Vernitron Piezoelectrics
Bl,B2,B3 MN1500 Alkaline Battery, Duracell
(-29C to +70C)
or
B4,B5 BR-2/3A-lP Lithium Battery, Panasonic
(-40C to +85C)
LCD1 Excelix 4320- Excel Technology, 4 Digit
RPQ-0 Display
LCD2 Excelix Flag Excel Technology, Custom LCD
LCD3 Excelix Flag Excel Technology, Custom LCD
Figure 3 shows the progress of a coin through the
coin chute 48. After the coin is introduced into the coin slot
81, it drops down the chute 52 and impacts on cellular urethane
shock absorbing material 50. The impact of coin 12 is dampened
by shock absorbing material 50 and transmitted to piezoelectric
transducer 14. The shock absorbing material 50 preferably
comprises a cellular urethane such a PORON~ No. 4701
manufactured by the Rogers Corporation. The signal produced by
the piezoelectric transducer 14 is integrated by the circuit 10
in Figure 1 to produce an output proportional to the mass of
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the coin 12. By rigidly controlling the fall of the coin 12
through a given unchangeable distance, it is possible to
accurately produce repeatable results. Therefore, a coin 12
falling through the chute 52 will always produce the same
impulse or impact on the piezoelectric transducer 14.
Accordingly, the integral of the impulse signal will always
produce the same result indicative of the mass of the coin.
Piezoelectric transducer 14 is preferably located at an angle
with respect to the fall of the coin 12 so as to allow the coin
to proceed on the track.
The signal output from the piezoelectric transducer
is illustrated by graphs 67 and 68 in Figure 5A. Graph 67 is
directly proportional to the impulse created by a ten cent coin
12 striking the PVC shock absorbing material 50. Without the
shock absorbing material 50, the impulse curve 67 would not be
as smooth. After coin 12 rolls away, the curve 67 returns to a
straight line. Waveform 68 represents the impact of a twenty-
five cent coin 12 for comparison purposes. The peak impulse of
voltage generated by the impact of twenty-five cent coin 12 is
approximately 8 volts. The 8 volt signal produced by transducer
14 represents the impulse, i.e. momentum of the twenty-five cent
coin 12. Signal 67 or 68 acts as an input to the integrator
subcircuit 16 formed by operational amplifier U1, resistor R4
and capacitor C1. The output of amplifier and integrator
circuit 16 is shown as waveforms 70 and 72 in Figure 5B.
Waveform 70 is the integrated output of the impulse created by
the fall of a twenty-five piece 12. Waveform 72 is the
integrated output of the impulse formed by the fall of a ten
cent piece 12. Since the integral of the impulse, i.e. momentum
of a coin is proportional to the mass, then it is clear that the
curves 70 and 72 are uniquely characteristic of the masses of
twenty-five and ten cent pieces 12, respectively.
Analog-to-digital converter 18 samples the output
waveforms 70 or 72 from amplifier and integrator circuit 16
every 100 microseconds under the control of microcomputer 20
and stores the peak voltage (P) in memory. If the peak P
exceeds a minimum threshold, indicating a possibly valid coin,
- 10 - 1336782
the microcomputer 20 prepares to turn LED circuit 26 on. How-
ever, before actually turning on the LED D4, the microcomputer
circuit 20 samples the output of the photodetector amplifier
30 and stores that value in memory as voltage a VO. Microcom-
puter 20 then turns on the current to the infrared LED D4 and
starts sampling the output voltage from the photodetector D5
as amplified by amplifier circuit 30.
After the coin 12 has passed the piezoelectric
transducer 14, it continues to roll down the chute 52 into the
vicinity of the optical path area 54. Figure 4A is a diagram-
matic representation of the coin 12 as it passes through the
optical area measurement zone 54. LED D4 produces an infrared
light beam 56 which illuminates collimating lens 58. The colli-
mated infrared beam 60 shines across the path of the coin 12.
Light 60 which is not eclipsed by coin 12 impinges on converging
lens 62 which produces a converging infrared beam 64 which in
turn impinges on photodiode D5. Center line 66 indicates the
relative alignment ~f the elements and the coin 12.
Figure 4B illustrates in cross-sectional detail
the manner in which the coin 12 eclipses the collimated light
beam 60. The coin 12 in the center o Figure 4B is shown in the
position of maximum eclipse of collimated infrared beam 60.
At that point, the maximum amount of light 60 is blocked by
coin 12 and the minimum amount of light 64 is received by photo-
diode D5. The output of photodiode D5 is sampled at very
short intervals by microprocessor 20 to determine the point of
minimal signal output which corresponds to the point of maximum
coin eclipse of the collimated beam 60.
Two typical optically generated waveforms 74 and
76 are shown in Figure 5C. Waveform 74 corresponds to the
voltage signal generated by the passage of a twenty-five cent
piece 12 whereas waveform 76 represents the signal generated
by the passage of a ten cent piece 12. Since the twenty-five
cent piece 12 is larger in diameter than the ten cent pice 12,
1 336782
-- 11 --
it stands to reason that the twenty-five cent piece 12 blocks
off more light than the smaller ten cent piece 12. Therefore,
the peak of the twenty-five cent piece waveform 74 is greater
than the peak of the ten cent waveform 76 since the twenty-five
cent waveform 74 represents the eclipse of more light and,
therefore, produces a greater voltage change across the output
of amplifier circuit 30. The output of circuit 30 is also
sampled by A/D converter circuit 18 under the control of micro-
computer circuit 20 which stores the maximum voltage Vp and
the minimum voltage VM in memory. Microcomputer 20 then com-
putes the following ratio:
A = VM - VO
Vp -- V
The ratio A is representative of the surface area
of the coin 12, and is invarient with respect to changes in
the LED intensity of diode D4, the photodiodie offset current,
or the velocity of the coin 12 as it passes through the lens
system 58 and 62. The ratio A and the output Peak voltage P
from the piezo amplifier and integrator circuit 16 are com-
pared against the stored acceptable range of values in the
coin identification and time programming memory circuit 32.
If a match is found within reasonably small tolerance values,
the coin 12 is identified and accepted as valid. If a match
is not found, the coin is identified as invalid. According to
the preferred embodiment of the invention, the coin 12, whether
valid or invalid, drops into a coin box. However, according
to alternative embodiments, the invalid coin could be rejected
and returned to the user.
The microcomputer 20 and the associated electronic
circuitry is normally in the dorrl~ant state during which the
device 10 draws a minimal amount of current VB from the battery.
VB is sufficient to drive the LCD and flag display 38 but not
sufficient to drive the LED D4. In the dormant state, microcom-
puter 20 is controlled by the 32.768kHz crystal controlled
clock 34. The 32.768kHz clock- rate is internally divided by
microcomputer 20 to provide precision timing pulses for the
.
.
~ - 12 - 1 336782
internal circuitry. During the dormant state, the remaining
time on the meter is displayed by circuit 38, the details of
which are illustrated in Figures 6H and 6I. The digital output
of the apparatus 10 is updated every minute until time has
expired as determined by the number of coins inserted into the
meter 10. A liquid crystal red flag 120 is energized to indi-
cate the "time expired" situation. The yellow flag 122 is
preferably used as an overtime feature on some meters to indi-
cate when the device 10 has timed down to zero time on the
meter. The red flag 120 is then used to indicate the end of
over-time limit (e.g. -2 hours). The preferred embodiment is
capable of counting up to minus 9 hours and 59 minutes. In
meters with no overtime feature, the yellow flag 122 will only
go on instantaneously as the circuit 10 passes through zero
minutes then the red flag 120 goes on and the LCD display 124
will count the time in minus numbers. The foregoing operation
would be typical of the use of the invention in the ~nited
States of America. However, in certain foreign countries,
such as Great Britain, it is contemplated that the yellow flag
122 will be on between zero time on the meter and the overtime
limit. After the overtime limit is reached, the red flag 120
will be on indicating a more serious violation. Since the
device 10 is capable of measuring up to minus 9 hours and 59
minutes of overtime with LCD display panel 124, it would be
possible to issue parking tickets in direct proportion to the
amount of overtime actually accrued.
The internal and external mechanical portions of
the invention are shown in detail in Figures 6A through 6I. A
parking meter housing 78 encloses all of the mechanical and
electrical elements. Coin entrance piece 80 is the first me-
chanical element encountered by the customer as he inserts a
coin 12 into the device 10. Coin slot opening 81 communicates
with coin chute 52 such as illustrated in Figure 3. Chute 52
is formed by a pair of mirror image frame pieces 82. Frame
pieces 82 are formed from outer track sections 85 and 87. An
~ - 13 ~ 1 336782
aperture 84 in the frame pieces 82 is positioned at right angles
across the path of chute 52. The chute comprises two regions,
namely the piezoelectric transducer region 52 and the photo-
sensor area region 54. An internal housing 86 for the photo-
diode section 28 and anohter internal housing 88 for the LED
electronic section 26 are located on opposite sides of aper-
ture 84 so as to scan the path of the coin 12 as it progresses
down the photosensor region of chute 54. A piezoelectric
holding bracket 94 is positioned up-stream of aperture 84 and
located so as to accommodate the piezoelectric transducer 14
and the cellular urethane impact pad 50. A track damper 93
shown in Figure 6C is used to minimize the bounce and jump of
the coin as it rolls down the chute 52 and 54. Attached to
main frame 97 is a bracket for supporting the piezoelectric
transducer 14 and damping pad 50. A rate plate bracket 95 is
also attached to the main frame 97 and serves to support a
conventional rate card. The rate card is not illustraed be-
cause it does not help to further understand the invention. A
return spring 99 attached to the coin translation box 90 re-
turns the flange 109 to its home position. Spring 99 also
serves to keep the translation box 90 away from wake-up limit
switch 44 unless the translation handle 98 has been manipu-
lated. A bracket 101 attached to main frame 97 serves to sup-
port tracks 85 and 87. A circuit board bracket 18 attaches
the electronics circuit board 107 to the back of the apparatus.
The circuit board 107 includes most of the active elements of
the invention 10 including the microprocessor 20. The LCD
board 38 is connected to the apparatus by a spacer 105.
A molded coin entrance transfer block 96 is shown
in detail in Figure 6F. Transfer block 96 includes a handle
section 98, a flange 109, an extension 100 and a pair of plates
forming a box-like section 102 for translating the coin 12.
Flange 109 serves to block the chute after a coin has been
inserted and is being translated. The translation section 102
` ~ - 14 - I 336782
starts the coin 12 on its journey down chute 52 in response to
manipulation of handle 98.
The coin entrance frame piece 80 is shown in greater
detail in Figure 6G. Handle slot 106 is adapted to receive
the extension section 100 of the coin transfer block 66. Move-
ment of the coin transfer block 96 along the length of slot
106 causes the translation box section 102 to move from the
slot entrance 81 to the point where it releases the coin down
chute 52. The coin entrance piece 80 includes a weather cap
section 108 which shields the coin slot 81 and the translation
handle 98 from rain, snow and other elements. The tapered
base 114 of the entrance piece 80 is shaped to center the coin
12 prior to its fall ~nto chute 52. Parallel grid openings
112 in the base 114 allow moisture to pass through the en-
trance piece 80 withcut damaging the chute 52. It also serves
to improve the resistance of the invention 10 from vandals who
might employ liquids to gum up the internal works, and prevent
entry into the coin measu:ing area of wires, etc.
In summary, the operation of the preferred parking
meter embodiment 10 of the invention proceeds as follows.
Initially, it is assumed that there is no time on the meter
and, therefore, the meter starts in the low power, dormant
state. The red flag 120 would be illuminated under such
circumstances. Starting with the foregoing assumptions, the
meter user first places a coin 12 in coin entrance slot 81.
The coin 12 is then held captive by the coin translation box
section 102 of transfer block 96. Next the meter user pushes
the transfer handle 96 along the length of slot 106 causing
the coin 12 to fall off of the ledge formed by tapered base
114 and to start down chute 52. The movement of the handle 98
also causes the transfer block to activate wake-up switch 44
causing the circuitry 10 to change from its low power dormant
state to its pre-active state. In the pre-active state, the
microprocessor 20 switches from the slow 32.768 kHz clock 33
1 336782
-- 15 --
to the higher frequency 400 kHz clock 35. The circuit 10 stays
in the pre-active state for 500 milliseconds and returns to
the dormant condition unless a signal is generated by the piezo-
electric transducer 14. Coin 12 next impinges upon the PVC
impact pad 50 which covers piezoelectric transducer 14. The
impact of coin 12 on piezoelectric transducer 14 produces im-
pulse waveforms similar to plots 67 and 68 shown in Figure 5A.
The impulse waveforms 67 or 68 are integrated by amplifier and
integrator circuit 16 and sampled by analog-to-digital converter
circuit 18. The maximum value of the integrated waveform (such
as 70 or 72 on Figure 5B) is stored in memory by microcomputer
unit 20 as a voltage P. The integrated signal produced by the
impact of coin 12 on piezoelectric transducer 14 is directly
proportional to the mass of the coin. If the voltage P is
larger than a minimum, threshold, the microcomputer brings the
circuitry to a fully active state. Next the coin passes through
the collimated light beam 60 producing an output signal similar
to waveforms 74 and 76 in Figure 5C. The troughs in the optical
waveforms 74 and 76 represent the net cross-sectional area of
the coin. Therefore, a coin such as a dime with a hole in it,
would generate a different waveform than a dime without a hole
in it. The output from photodiode D5 in detector section 28
is sampled by analog-to-digital converter 18 and that minimum
is also stored by computer 20. The stored value of the mini-
mum is converted to a ratio A previously described as follows:
VM ~ VO
A =
Vp - VO
The light area ratio A, being characteristic of
the net cross-sectional area of coin 12, is compared to accept-
able ratios A stored in the coin identi~ication and time program-
ming memory circuit 32. If the ratio A is unacceptable, the
coin is rejected either by sending it to the coin box or by
sending it through a reject chute. However, if the ratio A is
acceptable, then the microcomputer 20 next compares ths signal
- - 16 - 1 3 3 6 7 8 2
P which is representative of the maximum excursion of the inte-
grated waveform 70 or 72 shown in Figure SB. If the integrated
signal P is within the acceptable ranges stored in the coin
identification and time programming memory unit 32, then the
coin 32 is ultimately considered valid and forwarded to the
coin box. If the coin fails the integral test, then it is
either forwarded to the coin box and kept or forwarded to a
reject coin chute and returned to the meter user. Presuming
that the coin 12 has passed both the area ratio test A and the
integral test P, the microprocessor 20 will then direct the
LCD driver circuit 36 to cause the LCD readout section 124 to
digitally display the amount of time available on the meter.
The introduction of additional valid coins 12 into the device
10 will cause the microcomputer 20 to register more time on
the LCD readout 124. As the meter section 10 times out under
the control of the second clock 35, which operates at the clock
rate of 32.768 Hz, the time displayed on readout 124 decreases.
If the display reaches a certain minimum point, for example,
zero, the yellow flag 122 might be activated. As the meter
continues to time past zero then the red flag segmaent 120
will be activated when the overtime limit is reached. The
preferred device has the capability of keeping track of over-
time up to 9 hours and 59 minutes. On the average, it takes
about 300 milliseconds from the time that the coin 12 impacts
on the piezoelectric transducer 14 to the time the circuit 10
returns to its dormant state.
The preferred embodiment of the invention 10 com-
prehends use in the context of a parking meter. ~owever, the
basic coin discriminator 10 could also be used in other con-
texts. Note, for example, the use of the coin discriminator in
the context of a public telephone 126 as shown in Figure 7A.
Alternatively, the coin discriminator is shown being employed
in a conventional vending machine 128 as shown in Figure 7B.
The coin discriminator 10 just described in detail
has several major advantages over the prior art. First of
all, the device uses a small amount of power since it is only
17 1 33 67 8 2
in the high power active state for a short period of time.
Second, by eliminating many of the mechanical parts
associated with conventional parking meters and the like,
it is possible to substantially increase the reliability of
the parking meter due to the fact that the fewer parts wear
out. Third, since many of the parts are formed from
integratable electronic elements, it is possible to achieve
substantial reductions in cost due to increased economies
of scale. Fourth, the device is highly accurate because it
is controlled by a very reliable frequency standard. Fifth
and last, the device is capable of discriminating with
great precision between valid and invalid coins. The power
of coin discrimination is believed to be substantially
greater than that of conventional mechanical coin
discriminators.
There are certain features of the invention that
can be modified according to the teachings of the
invention. For example, while the preferred embodiment of
the invention comprehends the use of a wake-up switch 44 to
cause the device to change from the dormant state to the
active state, it is possible that the wake-up switch 44
could be eliminated and the impulse signal created on the
piezoelectric element 14 used as the wake-up signal. In
other words, the impulse signal generated by the coin 12
could serve the dual function of waking up the
microprocessor 20 and providing an electrical measurement
of the impact of the coin on the piezoelectric element 14
as well as turning on LED D4. The invention 10 could also
be associated with a coin reject chute which operates in
the conventional ~ashion to return a non-accepted coin to
the meter user.
Although various preferred embodiments of the
present invention have been described herein in detail, it
will be appreciated by those skilled in the art, that
variations may be made thereto without departing from the
spirit of the invention or the scope of the appended claims.
