Vending machine apparatus and method to prevent fraud and minimize damage from injected fluids

An apparatus and method for reducing vandalism and minimizing damage from liquids injected into apertures of a vending machine is described. An anti-salting module, having a housing with an integral tray for collecting liquids, is connected beneath a bill validator in a vending machine A rubber fillet is connected to the rear of the bill validator and directs injected fluids to the tray. A moisture sensor integral to the tray is connected to detection and control circuitry. When moisture is detected, the detection and control circuitry operates to interrupt power and control signals to the bill validator. Other external sensors, such as a second moisture sensor and a continuity sensor for monitoring the status of other vending machine components, may also be connected to the detection and control circuitry. After moisture has been detected, vending machine power and control signals can be restored only when moisture is no longer present, and a SET switch is depressed by service personnel.

FIELD OF THE INVENTION 
The present invention relates generally to an apparatus and method for 
reducing vandalism and minimizing damage to a vending machine from 
injected fluids. This invention is concerned with means for increasing the 
ability of vending machine components, specifically bill validators, to 
handle an increased volume of injected fluids. 
BACKGROUND OF THE INVENTION 
Vandals force fluids into the bill entryway of bill validators in an 
attempt to generate false vending signals in vending machines to obtain 
free product and coins. Because of a method used by vandals to perpetrate 
the fraud, those familiar with the vending machine industry call this 
fraud practice "salting". Certain vending machine types, such as can and 
bottle machines, are particularly susceptible to such vandalism because 
they are frequently placed in exposed and unprotected locations. Thefts of 
up to 100 cans of soda and loss of coins from the coin tubes have been 
reported in some locations. Further, the cost for cleaning up bill 
validators, coin mechanisms, and other related vending machine components 
after such an attack can easily exceed three hundred dollars. 
The liquids injected into a vending machine opening can cause extensive 
damage to the component associated with that opening. In addition, the 
liquids may drip into other machine components and cause direct or 
indirect damage, increasing the cost of repair. 
Attempts have been made to design an apparatus to reduce the damage from 
such salting attacks. For example, a rainwater/anti-salting shield for 
installation in vending machines was made to reduce the ingress of liquids 
along the coin path. Such shields are frequently swamped by the volume of 
the injected fluids during a salting attack, and provide no protection for 
a bill validator. 
One company, EIC of Jenison, Mich., manufactures a "Protection Unit" for 
bill validators which mounts inside the bill validator on the line side of 
a power transformer, and includes a moisture sensor that mounts in the 
entrance of the bill validator. The moisture sensor circuitry operates to 
remove power to the validator and to provide an alarm function when 
liquids are sensed. However, the bill validator must be disassembled for 
installation of the unit, and when moisture is sensed the vend line is not 
disconnected. Further, the unit does little to reduce the collateral 
damage produced by a salting attack. In addition, the moisture sensor of 
this unit is potentially exposed to tampering. Yet further, cleanup 
requires access to the moisture sensor. 
The Mid-South Services Company of Dallas, Tex. produces the "Vender 
Defender", which is a shield-type device for limiting the amount of fluid 
injected, into the entrance of a bill validator. This unit does nothing to 
remove power or provide other protection in the case of a salting attack. 
Other means, such as using slow blow fuses and ground fault interrupters, 
have been implemented to protect vending machines and their components 
from salting attacks. While these methods provide some protection, they 
tend to act only after damage has been done to a vending machine component 
such as the bill validator. 
SUMMARY OF THE INVENTION 
The anti-salting module of the present invention provides protection to 
bill validators and other vending machine components from insertion of 
conductive fluids into vending machine apertures. The anti-salting module 
consists of two parts, the first is the module itself which includes a 
T-cable for electronic connection, and the second is a rubber fillet which 
fits in the rear of the bill validator beneath a bill stacker. The fillet 
is designed to reduce the amount of liquids retained by the bill 
validator, and acts to direct injected fluids toward a moisture sensor in 
the anti-salting module to make detection easier. 
The anti-salting module is mounted external to the bill validator without 
the need to use additional hardware or to modify the bill validator. The 
module contains tabs or fingers and clips which connect to existing 
openings located beneath the bill validator. The anti-salting module can 
be attached to the bill validator without using any tools, and remains in 
place under the influence of gravity. A T-cable electronically connects 
the module to the ends of the cables from the bill validator and the coin 
mechanism. 
The anti-salting module has an integral tray to collect injected fluids and 
to direct them towards a drain. The drain accepts 1 inch diameter tubing 
which can be used to direct the injected liquid away from the vending 
machine components. An integral moisture sensor is located in the tray, 
and detection and control electronics are connected to the sensor. Other 
moisture sensors may be located in other parts of the vending machine and 
connect to the detection and control electronics of the module. Further, a 
continuity sensor and associated detection circuitry may be used to 
monitor status of other vending machine components. In addition, a set of 
alarm contacts are available to the vending machine owner which can be 
used to sound an alarm or siren, disable the machine dispensers, or turn 
off the vending machine entirely. 
When moisture is detected, AC power, vend and control signals from the coin 
mechanism or control system are interrupted to the bill validator by the 
anti-salting module. Thus, damage is reduced and false vends are 
prevented. The power and control signals to the bill validator are latched 
in an open state until moisture is removed and a SET switch is depressed. 
The SET switch is mounted in the anti-salting module, and can only be 
accessed by service personnel. 
After a salting attack, the tray of the anti-salting module must be cleaned 
before the bill validator can be repowered. An LED in the module, which 
lights when moisture is detected by the moisture sensor, aids in this 
cleaning operation. Once this LED is no longer on, then the unit can be 
returned to service by depressing the SET switch.

DETAILED DESCRIPTION 
FIG. 1 depicts an embodiment of the anti-salting module 1 and fillet 5 of 
the present invention. This embodiment is designed for use with a Mars 
Electronics International model VFM1 and VFM3 bill validator. It should be 
understood that other embodiments would be required for other models and 
for attachment to bill validators manufactured by other companies. 
Referring to FIG. 1, the anti-salting module 1 has a receptacle, cup or 
tray 2 for collecting fluids. The tray 2 is an integral portion of the 
module 1 and is formed into this shape when the plastic body which 
constitutes the module 1 is molded. The tray 2 contains a drain 3 and an 
integral moisture sensor 4, and is shaped so that fluids that would 
normally drip onto various vending machine components mounted beneath the 
bill validator, such as the coin mechanism, cash box, and vend switches, 
are directed over the moisture sensor 4 and to the drain 3. The moisture 
sensor 4 is comprised of two conductive strips or electrodes mounted into 
depressions in the tray 2. Detector circuitry (not shown) senses a change 
in resistance across the narrow portion of plastic between the electrodes 
when a conductive fluid is introduced. Thus, when a conductive fluid or 
moisture is detected in the tray 2, the detector circuitry acts to 
disconnect power and control signals as described below. 
The anti-salting module 1 has extensions or fingers 6 which are designed to 
slip into vertical openings between the mounting bezel and the body of a 
bill validator (shown in FIGS. 2, 3 and 4). Shaped wire clips 8, mounted 
to the rear of the module 1, are designed to slip into existing openings 
in the rear of the bill validator. When connected, the anti-salting module 
1 is secured to the bottom of a bill validator under the influence of 
gravity. 
The fillet 5 is a molded piece of rubber designed to fit into the rear of 
the bill validator beneath a bill stacker. The fillet 5 directs injected 
fluids into the tray 2, and is discussed below with reference to FIG. 4. 
The details regarding the operation of bill validators, coin mechanisms and 
other vending machine mechanisms or control circuitry are not part of the 
present invention and will not be described in detail. However, the 
present invention physically and electronically attaches to a bill 
validator of a vending machine, and therefore some details regarding 
vending machine operation are discussed below. 
FIG. 2 depicts the anti-salting module 1 attached to a partial bill 
validator assembly 101. A face plate or bezel 102 has a bill opening 104 
through which conductive fluids are injected by vandals. (Like components 
are numbered the same in the figures.) Various bill validator mechanisms, 
such as the bill transport and validation system, have been removed to 
show the various openings through which fluids would flow into the tray 2, 
and to illustrate how the anti-salting module 1 is connected. As shown, 
fingers 6 and wire clips 8 attach to existing openings of the assembly 
101. 
FIG. 3 depicts the assembly of FIG. 2 rotated 90 degrees to show the 
underside of the anti-salting module 1. An electronics compartment 10 
having a cover 11 is shown. The electronics compartment 10 holds the 
moisture detection and control circuitry in an enclosed area located below 
the tray 2. A moisture present LED 82 and a SET switch 84 are also shown, 
and are discussed in detail below. The drain 3 can accept one inch 
diameter flexible tubing to allow collected liquids to be piped into an 
area where they will do no harm. Also depicted in FIG. 3 are a 4-pin 
connector 12, and a 14-pin connector 18, which are discussed below. 
FIG. 4 is a partial cutaway side view, not drawn to scale, of a vending 
machine 200 showing a typical component layout along the vending machine 
front panel 210. FIG. 4 also shows the anti-salting module 1 and fillet 5 
connected to the bill validator 100. The anti-salting module 1 and fillet 
5 can be fitted to existing bill validators without the use of additional 
hardware, and without modifying or removing the existing validator from 
the front panel 210. The front panel 210 contains bill validator bezel 
102, a bill opening 104, exact change light 108, coin slot 152 and coin 
return chute 154, which are accessible to customers of the vending 
machine. The module 1 mounts directly beneath the bill validator 100 
inside the vending machine 200, and is accessible only to service 
personnel, not to customers using the vending machine. Plastic tubing 20 
is connected to the module 1, and is used to drain fluids collected in the 
tray 2 away from the vending machine components to a bucket or some other 
drainage means (not shown). The tubing 20 could be made of rubber, plastic 
or other materials and comprise tubing, pipe or any other type of conduit 
for channeling the liquid. A coin mechanism 150 is also shown having a 
coin slot 152, coin track 153 and a coin return chute 154, and is mounted 
above the cash box 160. An external moisture sensor 45 can be placed in 
the coin track 153, and is electronically connected to the detection 
circuitry of the module 1, as explained below. 
The fillet 5 of the present invention is inserted into the rear of the bill 
validator 100 under the bill stacker 110, as shown, to block fluid from 
flowing into the validator. The fillet 5 also directs fluids into the tray 
2 to trigger the moisture sensor 4, and for draining liquid away from 
other sensitive circuitry. 
FIG. 5 is a simplified block diagram showing the electrical connections of 
the anti-salting module 1 depicted in FIG. 4. The module 1 is connected 
via a T-cable 30 and two 9-pin connectors 32, 34 to the bill validator 100 
and the coin mechanism 150. The coin mechanism 150 is normally connected 
directly to the bill validator 100, via cables 105 and 155, to provide 
power to the validator and to permit the exchange of signals. As shown, 
the bill validator 100 and coin mechanism 150 plug directly into the 
anti-salting module 1. A power supply is integral to the anti-salting 
module 1 and is powered from AC power obtained from the coin mechanism 
cable 155. 
The electronic control circuitry for the anti-salting module is mounted in 
an electronics compartment 10 (shown in FIG. 3) located beneath the tray 
2. Both strips of metal which comprise the moisture sensor 4 are connected 
to a PC board (shown in FIG. 3) by a screw or stud (not shown) which 
passes vertically through the floor of the tray 2 and into the electronics 
compartment 10. The bottom of the tray 2 remains sealed. Thus, the PC 
board and electronic circuitry in the electronics compartment 10 of the 
anti-salting module 1 are protected from liquids (See FIGS. 1 and 3). A 
14-pin connector 18 allows for connections of the T-cable 30 to both the 
coin mechanism 150 and the bill validator 100 of FIGS. 4 and 5. A 4-pin 
connector 12 allows other functions to be added to the vending machine 200 
for added protection. For example, another moisture sensor 45 could be 
added elsewhere in the machine, or a continuity sensor 47 could be added 
to detect if any components, panels, or assemblies in the vending machine 
200 were moved or damaged in any way. 
FIG. 6 is a block diagram of an embodiment of the circuitry of the 
anti-salting module 1. A power supply 50 supplies 12 volts of power 
through a transformer (shown in FIG. 7A), and isolates the electronics 
from AC power so that power leakage will not occur in the presence of 
liquids. A moisture detector 40 is connected to the electrodes of the 
moisture sensor 4 mounted in the bottom of the tray 2. The output of the 
moisture detector 40 goes high if moisture or a conductive liquid is 
sensed. An external moisture sensor 45 can also be connected to the 
moisture detector 40 to monitor for moisture in another part of the 
vending machine. A continuity alarm 43 can also activate the moisture 
detector 40 if an external continuity device 47 in the vending machine 200 
senses a change in state of another part of the vending machine, such as 
damage to a front door assembly. This can be used to ensure integrity of 
other vending machine functions that may suffer from tampering. 
Reset circuitry 60 accepts the output of the moisture detector 40 and 
generates a single 20 ms or greater pulse when this level goes from a low, 
approximately one volt or lower, to high, typically 10 volts or higher. 
This pulse is delivered via line 62 to the reset coils of three latching 
relays (shown in FIG. 7A) in latching relays block 70, whose set and reset 
coils are connected in parallel. Each relay will latch in one position and 
remain there even in the absence of power, remembering the state into 
which they were last driven. When moisture is detected the reset coils of 
the latching relays are powered momentarily, latching them in the reset 
position. Five of six sets of latching relay contacts are used to remove 
AC power and control lines from the validator. The sixth set of contacts 
can be used to inhibit machine operation, to disable the coin mechanism 
from paying out coins, to operate an alarm or timed siren, to remove power 
from the entire vending machine, or a combination of these. The latched 
unpowered state can render the entire machine inoperable. This allows the 
operator to become aware of the contaminated state of the machine and 
initiate remedial action so as to reduce the corrosion to the bill 
validator, coin mechanism and the vending machine. 
When power is removed from the bill validator 100 due to moisture, the 
alarm contacts of the relays are set in the active position. This is 
called the reset or unpowered state. This is particularly important since 
having AC power connected to the bill validator in the presence of a 
conducting liquid is very destructive. Shorts and conduction paths are 
created both across the AC line and to low voltage circuitry which may 
cause extensive damage and makes repair very difficult. Removal of power 
prevents the bill acceptor motor from running and spreading the conductive 
liquid up into the electronics and bill stacker assembly. Further, the 
vend relay line is broken (opened by a latching relay), so that no 
spurious bend pulses can be generated by the bill validator. Thus, the 
cause of multiple phantom vends are removed which normally result in coins 
and product being paid out by the vending machine during a salting attack. 
Additionally, two AC line related signals associated with enabling and 
inhibiting are required to support some bill validator interfaces. These 
lines are also opened by use of a latching relay. All of these lines, five 
in number, are broken and then latched in the open state (no AC power, no 
vend, no control lines) so that removal of AC line power from the vending 
machine at the wall outlet, and then reapplication of AC line power, 
cannot cause these contacts to be closed and return the validator to 
operation. This prevents later damage to the bill validator, perhaps 
during service and cleanup, as well as preventing the vandal from 
re-powering the vending machine to obtain product or money. 
The output of the moisture detector 40 also drives the Set block 80. The 
Set block 80 turns on a moisture present LED 82 when moisture is detected. 
In addition, it provides the output pulse to drive the set coils of 
latching relays into the Set or Operate condition when a Set switch 84 is 
depressed. This pushbutton is integral to the module. When the SET switch 
84 is depressed, the contacts of the relays in the unit move to their set 
position and return normal functionality to the validator only if the 
moisture detector determines that moisture is no longer present. This 
ensures that the affected unit is serviced and not just repowered. This 
can result in a timely repair which will reduce damage to the unit. The 
moisture present LED 82 aids the service technician in the cleaning of the 
unit. 
Power Up/Down detect circuitry 90 inhibits the Reset circuitry 60 so that 
the status of the latching relays does not change when AC power is applied 
or removed from the bill validator, or from the vending machine. This 
prevents false triggering of the reset coils of the latching relays when 
Ac power is changing. 
MOISTURE DETECTION 
Moisture is detected when fluids connect the two electrodes of the moisture 
sensor 4 which changes the resistance across the electrodes. This occurs 
because the resistivity value of water and other fluids is much smaller 
than that of the plastic insulation and air that separates the two 
electrodes. 
An embodiment of the moisture sensor 4 of the present invention comprises 
two metal electrodes, each 54 mm long, separated by about 2 mm of the 
plastic tray material. The plastic has a bulk resistivity of approximately 
1.4 to 1.5.times.10.sup.14 ohm/cm. Thus, the resistance across the 
electrodes without any liquid present is about 4.times.10.sup.11 ohms. So, 
with a 2 mm separation and a 1 mm conduction path for the liquids, the 
resistance R is approximately as follows: 
R=4.times.10.sup.11 ohms for no liquid; 
R=2.times.10.sup.4 ohms for ordinary water; and 
R=2.times.10.sup.3 ohms for sea water. 
In practice, although some leakage through the electrodes occurs, the 
conduction path for liquids is wider, resulting in even lower resistance 
values across the electrodes when a liquid is present. Consequently, the 
presence of liquids produces a dramatic change in resistivity which is 
easily sensed. 
CIRCUIT DESCRIPTION 
FIGS. 7A and 7B depict an embodiment of the moisture detection and control 
circuitry of the present invention. Referring to FIG. 7A, the power supply 
circuitry 50 receives 117VAC power from the coin mechanism 150 via the 
T-cable 30 which is plugged into the 14-pin connector 18 or P1 on the PC 
board. AC power enters on pins 6 and 7 of P1 and is used to drive the 
input side of transformer T1. AC power leaves P1 via pins 13 and 14 to the 
bill validator 100 if the relay K2 is in its normal set position. 
Transformer T1 steps down the AC line voltage and isolates the circuitry 
from the AC line. The AC voltage at the secondary of T1 is rectified by 
the diode bridge D1. Capacitor C3 filters the pulsating DC appearing at 
the input of the voltage regulator U1. Capacitors C1 and C2, located on 
the primary and secondary sides of T1, are used to lower line noise. 
Capacitors C4 and C5 provide filtering of the output of the 12 V linear 
voltage regulator U1. 
For purposes of the following discussion, the range sensitivity jumper, 
shown in FIG. 7B, is in the normal (JP1) position and jumper JP3 is in 
place. Thus, the moisture detection and control circuitry is set to 
function with normal sensitivity and without a continuity sensor. The 
function of jumpers JP1, JP2 and JP3 is discussed in detail below. 
The moisture detector circuitry 40 uses two sections of a quad LM224 
operational amplifier integrated circuit, U2B and U2A. U2B is used as a 
high impedance voltage follower while U2A is used as a comparator. One of 
the terminals of the moisture sensor electrodes 4, which is integral to 
the tray 2, is connected at the junction of resistors R9 and R10. The 
second terminal of the integral moisture sensor 4 is connected to ground. 
Thus the moisture detector forms a voltage divider as a third resistor to 
ground which is in series with R8 and R9. This is the point that is 
presented to the noninverting input of U2B via resistor R10. If there is 
no moisture present across the terminals of the electrodes in the tray 2, 
the resistance across these terminals will be many megohms in value. This 
may range from 10 to many hundreds of megohms. This is a measurement of 
the leakage of the plastic which is used to mount and separate the 
moisture sensor electrodes. The input impedance of the voltage follower 
U2B will be 40 megohms or greater. Thus, the voltage at the junction of R9 
and R10 will be an appreciable fraction of the 12 volt supply, since the 
impedance at the top of capacitor C8 looking up towards the 12 volt supply 
is only 1.32 megohms while that looking down towards ground will be many 
megohms. If the resistance of the sensor in parallel with the input 
impedance of U2B is 11 times that of the sum of R8 and R9, then the 
resistance is approximately 14.5 megohms. This means that the voltage at 
C8 will be about 11 volts. Since very little current flows into the 
noninverting input of U2B, then the voltage at the noninverting input (pin 
5) will be nearly 11 volts as well. 
Since U2B is a voltage follower, the output of U2B (pin 7), will equal its 
input or be 11 volts. Diode D8 will charge capacitor C9 until the voltage 
across D8 and C9 plus that at the junction of R15, R16 and C10 is equal to 
11 volts. The voltage at the junction of resistors R15 and R16 is about 
1.3 volts. Since after some initial charging, very little current flows 
through D8 (5 microamps through R13 and R14 plus a few microamps or less 
of leakage through C9) the voltage drop across this diode will be 0.5 
volts or less. This means that capacitor C9 will have about 9.2 volts 
across it. The divider R13 and R14 will divide this in half so that the 
voltage at the noninverting input of the comparator U2A will be 
approximately 5.9 volts. Since the voltage at the inverting input of U2A 
is 11 volts, and the inverting input voltage is much greater than the 
noninverting input, the output of U2A will remain low. 
If a conductive fluid is now placed across the terminals of the moisture 
sensor, the impedance across C8 will drop to less than 10K ohms. The exact 
amount the impedance drops depends upon various factors including how much 
liquid is present, how conductive it is, the area of the sensor involved, 
and the type and temperature of the liquid. Assuming that the resistance 
drops to 10 K ohms, since resistors R8 and R9 form a voltage divider with 
the sensor, the voltage across C8 will now be under 100 mv. Thus, the 
input of U2B will drop to under 100 mv, and the output of U2B will go to 
under 100 mv. Diode D8 prevents the charge on capacitor C9 from changing 
rapidly since now its only discharge path is through R13 and R14. Hence 
the noninverting input of U2A will remain at the same value as earlier, 
about 5.9 volts. Since the voltage at the inverting terminal is about 90 
mv, the output of U2A will swing high, driving current into the base of 
transistor Q5 of set block 80 and causing collector current to flow to 
turn on the moisture present LED 82. 
The positive going edge from U2A will also be coupled through capacitor C11 
and resistor R17 of reset block 60 to ground. This differentiated signal 
from the output swing of U2A, approximately 10 V, will produce a spike of 
about the same size, but decreasing in time by the RC action of C11 and 
R17. A portion of this spike presented via resistor R18 of reset block 60 
to the noninverting input of U2C will be greater than the voltage present 
at the inverting input, so the output of U2C will go high. As capacitor 
C11 charges, the voltage at pin 10 of U2C will drop below that at pin 9, 
and the output of U2C will go low again. For as long as the output of U2C 
is high, transistor Q4 will receive base drive and pull low the reset line 
of the three latching relays K1, K2 and K3 of FIG. 7A. Current flows 
through the reset coils of these devices, latching them in the reset 
position to remove power to the validator and to assert the alarm contacts 
that go to 14-pin connector 18 pins 1 and 2. In the reset circuitry 60, 
capacitor C12 provides a filter for the reference voltage at the junction 
of resistor R19 and R20, and resistor R18 at the noninverting input of U2C 
is used to suppress operation of the Reset circuitry during power up and 
down, which is described in detail below. 
Referring to FIG. 7A, diode D9 in the latching relay block 70 limits the 
inductive kick from the coils when transistor Q4 in the reset block 60 
turns off. It should be noted that no further signal is needed to keep the 
relays in the reset position to hold the validator unpowered, and that the 
relays retain this state even if 12 V power is removed. 
Referring to FIG. 7B, the arrangement of diode D8, capacitor C9, resistors 
R13 and R14, and the comparator U2A in the moisture detection block 40, 
form an adaptive comparator that looks only for the signal to change to 
some fraction of a quiescent, prior value. With the values as shown in 
FIG. 7B, the threshold is such that the value of the signal must change to 
approximately 50% (ignoring the effect of R15 and R16) of its quiescent 
value. Thus, if leakages cause the output of U2B to rest at 8 volts, 
operation of the moisture detector circuitry is unimpaired when moisture 
is detected and the output of U2B changes to under 4 volts. If 
consideration is given to the presence of the bias network of R15 and R16, 
then the 8 volts signal at the output of U2A must change to below about 
4.4 volts. The amount of change required can be controlled by changing the 
ratio of resistor R13 to R14. The addition of the bias network supplied by 
resistors R15 and R16 adds a low limit threshold that causes operation of 
the comparator U2A if the output of U2B drops below about 1.3 volts, 
independent of its prior state. These two techniques combat the problem of 
leakage through the moisture sensor, which may impair the correct 
operation of the moisture detector circuitry, that may occur with age, use 
and environment. 
Sensitivity of operation of the detector circuitry may be changed by using 
a jumper across either JP1 or JP2. Thus, the sensitivity of the moisture 
sensor may be decreased to handle humid locations or situations. With a 
jumper across JP2, resistor R9 is shorted out and thus larger leakages can 
be handled across the moisture sensor elements without triggering the 
reset condition of the relays. Sensor resistance of 100K ohms or less can 
be accommodated without loss of functionality. The jumper plug is stored 
on the two pins associated with JP1 when it is not used at position JP2, 
and there is no ohmic connections to the pins of JP1. 
An external moisture sensor (outside the tray) could be mounted at some 
other place in the vending machine, such as on or in or under the coin 
track that leads from the coin slot on the front of the machine to the 
coin cup at the entrance of the coin mechanism. The sensor could consist 
of two electrodes on an insulator, a piece of flexible PC board material, 
or contacts to two screw heads mounted on a plastic or insulating 
substrate. Fluid injected into the coin slot could thus be detected by the 
external sensor along this path which would trigger the moisture detector 
circuitry 40 and force the latching relays into their reset position. 
Thus, power would be removed from the bill validator and the set of alarm 
contacts (upper set of contacts of relay K1) would be moved to the active 
state, which could directly or indirectly remove power to the coin 
mechanism or the vending machine as well as activate an alarm or siren. 
Referring to the latching relays block 70, fuse Fl is used to limit 
current through the alarm contacts used by the owners to protect their 
vending machines. 
Resistor R26 and capacitor C8 are connected to pin 4 of the 4-pin connector 
12, and are used as a filter to reduce noise that might result from use of 
an external moisture sensor. Resistor R10 and diodes D5 and D6 protect the 
input of the voltage follower U2B, and capacitor C10 filters the voltage 
reference provided by resistors R15 and R16. 
Referring to FIG. 7A, relays K1, K2 and K3 of latching relay block 70 
remain latched in the reset position when tripped, removing power and 
signals from the validator until the set coils of the relays are 
activated. The relays can be set to return power and functionality to the 
bill validator only by depressing the SET pushbutton 84 in set circuitry 
80 (see FIG. 7B) with no moisture present at the sensor. If moisture is 
present at the sensor, such that the output of U2B is less than the 
voltage at the junction of R15 and R16, then the output of U2A will remain 
high. This keeps transistor Q5 active and keeps the LED 82 illuminated to 
indicate that moisture is present. Hence, because the collector voltage of 
Q5 is low, depression of the SET switch 84 will not cause transistor Q6 to 
turn on to set relays K1, K2 and K3. The moisture sensor 4 must be cleaned 
and dried so that the output of U2A is low before setting of the latching 
relays can take place. The presence of the LED 82 provides a guide as to 
the effectiveness of the cleaning of the moisture sensor 4. When the LED 
82 is off, this indicates that the output of U2A is now low and setting of 
the latching relays K1, K2 and K3 is possible. 
When the LED 82 is no longer illuminated, the collector of Q5 is high. 
Thus, depression of the SET switch 84 now provides base drive to 
transistor Q6 via the path resistor R23, LED 82, and resistor R25. 
Transistor Q6 forces current through the set coils of the latching relays 
K1, K2 and K3, and moves them to the set position. This action returns 
power to the bill validator, connects signals to and from the bill 
validator to the rest of the vending machine, and moves the alarm contacts 
from their active to their passive position. Diode D10 at the collector of 
Q6 is used to suppress the turn off transient signal associated with these 
coils. Resistor R24 is used to lower the input impedance of the base of 
transistor Q6 when SET switch 84 is open so that noise cannot trigger 
transistor Q6 into conduction. When the moisture sensor is clean and the 
SET switch 84 is depressed, the LED 82 will illuminate for as long as the 
switch is depressed, indicating that setting of the latching relays is 
taking place. 
During application and removal of AC power, information received from the 
integral moisture sensor and other sensors may not be reliable. To 
suppress these transient effects, the Reset circuitry 60 is inhibited 
during these times. To suppress undesirable behavior during the time when 
AC power has just been applied, power up detection circuitry 90 (see FIG. 
7A) comprising U2D and its associated circuitry is used. When AC power is 
applied, capacitor C7 is discharged. When the voltage begins climbing from 
zero to 12 volts, capacitor C7 begins charging through R4 slowly. The 
voltage at the noninverting input of U2D is produced by resistors R19 and 
R20 along with capacitor C12 of Reset block 60, which climbs quickly 
because of the short time constant associate with these components. Since 
the voltage at the inverting input is less than the voltage at the 
noninverting input of U2D, the output of U2D goes high turning on the 
transistor Q2. When Q2 turns on, it forces the noninverting input of U2C 
of Reset block 60 to nearly ground. This effectively inhibits the 
functioning of the Reset circuitry 60. As C7 charges, its terminal voltage 
passes through the voltage level generated by R19 and R20, at which point 
the output of U2D goes to the normal low state. When this occurs, 
transistor Q2 is no longer conducting and normal operation of U2C is 
allowed. Diode D4 and resistor R4 act to discharge C7 when power is 
removed. 
When AC power is removed, the power up detection circuitry 90 suppresses 
any operations during this time. Capacitor C6 is charged to about 10 volts 
at this time, and this charge cannot be changed instantaneously. 
Transistor Q1 is thus held on by current flowing through resistors R1 and 
R2. As the 12 volt supply begins to drop, the junction of C6, R1 and R2 is 
forced towards ground and finally lower than ground, so that transistor Q1 
no longer receives base drive and turns off. The collector of Q1 goes high 
and acts as a source of current via R3 for resistor R6 to turn transistor 
Q2 on and thus to hold the reset circuitry 60 inoperative. Diode D2 and 
resistor R1 provide a discharge path for C6, as do resistor R2 and diode 
D3. The primary function of diode D3, however, is to protect the base of 
transistor Q1 from reverse voltage breakdown by the action of C6. 
To allow for the inclusion of an open alarm where continuity is assumed 
normal and an open is abnormal, the continuity detection circuitry 43 of 
FIG. 7B is used. For example, a conductive foil strip might be attached to 
the rear of the Exact Change light to monitor its status. If the Exact 
Change light is disturbed, the conductive foil would be ruptured and cause 
an open circuit to occur. If jumper JP3 is removed then a continuity 
sensor is being used. If an external short is present in the machine from 
pins 2 to 1 of 4-pin connector 12, the External Sensors connector, then 
current will flow from resistor R11 through the external short and back to 
ground. Hence, the voltage at the junction of R11 and R12 will be very 
low. This will rob transistor Q3 of its base drive and keep it turned off. 
If an interruption of the conduction path between pins 2 and 1 occurs, 
then the voltage at the junction of R11 and R12 will climb and transistor 
Q3 will turn on. This will pull the noninverting input of U2B to ground 
and trigger the Reset condition to remove power and signal from the bill 
validator and generate the alarm condition. Diode D7 is a clamp to prevent 
the base of Q3 from going more than a diode drop below ground. Continuity 
sensors can be provided by other means such as switches, reed switches and 
magnets, or actual wires. 
An alarm can be added to the anti-salting module 1 to provide an acoustical 
indication of the resent state. Further, either an integral or external 
delay can be added to provide drive for an alarm, horn or siren. In 
addition, the techniques described above can be used to remove power from 
the coin mechanism, the bill validator, the vending machine dispensers, or 
other portions of the vending machine. 
In summary, the present invention provides a method and apparatus for 
preventing fraud and minimizing damage to a vending machine from injected 
liquids. The anti-salting module 1 attaches to existing bill validators 
without requiring their disassembly, and without the need for special 
hardware. Further, the cables from the coin mechanism and bill validators 
connect directly to the module without requiring any modification. The 
design of the module 1 prevents tampering with the moisture sensor 4, and 
provides for easy clean-up and resetting of the vending machine after a 
salting attack occurs. Fraud is prevented by using latching relays to 
disconnect power, which relays continue to interrupt the power and control 
signals until service personnel clean the tray of moisture and depress a 
SET switch which is integral to the module. Damage to vending machine 
components is minimized by collecting fluid in the tray, and draining it 
away from the components. 
While the present invention has been described in connection with a 
preferred embodiment, it should be understood that other embodiments may 
fall within the spirit and scope of the invention.