EP0241534A1 - Switching control apparatus for vending machine alternating current device switching - Google Patents

Abstract

Improved apparatus (1) for switching control of a number of alternating current (AC) devices (20), such as alternating current motors for prepayment machines, using a reduced number of switching elements ( 10) AC power such as relays by dividing AC devices into two groups and using a switching element (K7) to select the desired group, and using an additional number of switching elements (K1-K6) of alternating current each of which is connected to one of the alternating current devices in each of the two groups to determine which of the alternating current devices should be activated. Preferably, an additional alternating current switching element (Q1) is used to regulate the current flowing to the alternating current switching element determining the group so as to minimize the switching transients.

Description

Switching Control Apparatus For Vending Machine Alternating Current Device Switching

BACKGROUND OF THE INVENTION

1. Field of Invention This invention relates to improved switching control apparatus for reducing the number of alternating current (AC) power switching elements for controlling the activation of AC devices in vending machines, and particularly to a reduction in the number of such control elements, e.g., the relays used where a diode matrix arrangement is not practical. One example of such an arrangement in a vending machine is where a plurality of either AC motors or solenoids are employed as vending mechanisms for the delivery of products.

2. Description of the Prior Art

In simplified terms, vending machines typically include a selection mechanism which the user uses to communicate a selection or selections to the vending machine, one or more money recognition devices, such as a coin validator or a currency validator for recognizing whether inserted money is acceptable or not, a plurality of vend delivery devices or vend mechanisms for delivering a selected item to the vending machine user if adequate credit has been established and other vend conditions have been satisfied, and finally a control system for determining whether all vend conditions have been satisfied and for producing a vend signal if they .5 have been satisfied.

In older vending machines, there has generally been a one-to-one correlation between the number of vend delivery devices and the number of vend control elements used to control the activation of the delivery devices. The vend control elements took on several forms. In one known arrangement, each vend delivery motor had an associated selector switch which was used to complete the electrical circuit to one side of its associated vend motor, and 5 the money recognition system via a vend relay authorized the vend by completing the circuit to the other side of the motor under the appropriate conditions. See, for example, U.S. Patent No. 4,220,235. In another known arrangement, a separate 0 power control device is included in the control system for each vend delivery device. See, U.S. Patent No. 3,841,456. These arrangements having a one-to-one correspondence between control elements and delivery devices are operationally sound but economically 5 undesirable as they require a large number of costly control elements where a large number of dispensing devices are employed.

More recently, control systems have been developed which include matrix addressing arrangements 0 for addressing a plurality of vend delivery devices and reducing the number of control elements employed for the purpose of activating the delivery devices. See, U.S. Patent No. 4,458,187 assigned to the assignee of the present invention and U.S. Patent :5 Nos. 4,354,613 and 4,284,206. These arrangements may be described as n x m matrix arrangements where n is the number of rows in the matrix, m is the number of columns in the matrix, and n x m is the number of vend delivery devices in the apparatus. In these machines, the number of control elements is reduced to n + m or, in other words, one control element for each of the rows and columns in the vending machine. Such arrangements are particularly useful where diodes or some other simple means can be used to avoid activation of undesired vend delivery devices in the matrix. Neither diodes nor other sufficiently inexpensive means exist for preventing such undesired activation of alternating current motors or solenoids wired in a matrix array. Consequently, matrix arrays as previously known in the vending field have been inappropriate where alternating current motors or solenoids are used as delivery devices.

SUMMARY OF THE INVENTION The present invention is an improved switching control apparatus which does not require a one-to-one correspondence between AC power switching elements and AC devices, and which is suitable for use with a plurality of delivery devices such as AC motors and solenoids. Consequently, the present invention addresses the problem of reducing the number of components required to control a plurality of delivery devices in a vending machine, and avoids the problems of undesired activation which occur if AC motors or solenoids are connected in known vending delivery device matrix arrays. The invention is generally applicable to the problem of switching any AC devices in vending machines which must be switched on and off with any frequency.

Briefly, improved switching control apparatus according to the present invention uses a reduced number of AC power switching elements, such as relays, by dividing the AC devices to be activated into two groups and using one switching element to select which of the two groups is to be selected, and using an additional number of AC power switching elements each of which is connected to one of the AC devices in each of the two groups to select which one of the AC devices is to be activated. This arrangement reduces the number of AC power switching elements from the 2N required to switch 2N AC devices where there is a one-to-one correspondence, to N + 1. For example, in a prior art one-to-one arrangement for activating six AC devices, six switching elements are required.

The arrangement of the present invention employs only four AC power switching elements, such as relays, to activate six AC devices such as AC vend motors. According to the invention, the six vend motors would be divided into two groups of three in which each group of three motors shares one terminal in common. Each one of three of the relays is connected to AC neutral as well as to the other terminal of one motor, in each group so that the position of the wiper blade of each of these three relays determines which of the two associated motors has its non-common terminal connected to AC neutral. The fourth relay is connected to an AC hot line or AC power, and both the common terminals of the two groups of motors so that the position of its wiper determines whether AC power is connected to one group or the other group. This arrangement in conjunction with suitable control means for controlling the switching of the relays can be used to simply and inexpensively activate any one of the six motors. Finally, preferably, a further AC power switching element is used to control the flow of power to the group determining, AC power switching element so that switching transients can be minimized.

Further features of my invention, its nature, and various advantages will be more apparent upon consideration of the attached drawings and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified schematic diagram illustrating switching control apparatus according to the present invention in a rest state in which none of the vend mechanisms shown in the figure has been selected;

FIG. 2 is a second simplified schematic diagram illustrating switching control apparatus according to the present invention in an active state in which one of the dispensing devices has been selected; and

FIGS. 3A and 3B are a detailed circuit diagram of a control circuit for use in the preferred embodiment of the present invention, and in which the relationship of the control means of the switching control apparatus to an overall control system for a vending machine is illustrated.

While specific types of logic circuits are disclosed in connection with the embodiments described below in detail, other logic circuits can be employed to obtain equivalent results without departing from the invention.

DETAILED DESCRIPTION Figs. 1 and 2 illustrate the working of a switching control apparatus 1 having a plurality of AC power switching elements 10 and vend mechanisms or delivery devices 20 which are connected as described below. Figs. 1 and 2 illustrate the connection of AC power switching elements 10 and vend mechanisms 20 according to the present invention; however, they do not show control means for controlling the switching of the elements 10 and detailed discussion of suitable control means is postponed until the detailed discussion of Figs. 3A and 3B below.

As shown in Fig. 1, the plurality of control elements 10 include seven relays K1-K7, and a power switching device Ql which is shown as a triac, but could be some other suitable power switching device such as an additional relay. The plurality of vend mechanisms 20 includes two columns of six delivery devices VMA1-VMA6 and VMB1-VMB6 which are designated column "A" devices and column "B" devices. As shown in Fig. 1, a 115VAC line is connected to an input 11 of triac Ql. A second input 12 of the triac Ql is connected to a means for producing a control signal which is not shown in Figs. 1 and 2. When a control signal is present on the input 12, power flows through the triac Ql and from its output 13 to contact K7A of relay K7 since contact K7A is connected to output 13 of triac Ql. A second contact K7B of relay K7 is connected to one terminal of each of the column B delivery devices VMB1-VMB6. A third contact K7C of relay K7 is connected to one terminal of each of the column A delivery devices VMA1-VMA6. The position of relay K7's wiper blade K7W determines whether the output 13 of triac Ql is connected to column A or column B. As shown in Fig. 1, no current is flowing in the coil of the relay Kl, and consequently triac Ql is connected to column B. If current is caused to flow through the coil of relay K7, then wiper K7W moves to connect contact K7A to contact K7C and column A is connected to the triac Ql. Means for controlling the current in the coil of relay K7 and consequently for controlling the switching of the relay K7 is not shown in Figs. 1 and 2.

Having described the connection of one terminal of each of the twelve vend mechanisms 20 to 115 VAC, the connection of the other terminal of each of the vending mechanisms devices 20 will next be described. Each of the relays K1-K6 also has three contacts A, B and C and a wiper blade W. Each of the contacts K1B-K6B is connected to an associated one of the delivery devices VMA1-VMA6 respectively. For example, contact K1B is connected to delivery device VMA1. Similarly, each of the contacts K1C-K6C is connected to an associated one of the delivery devices VMB1-VMB6. For example, contact K1C is connected to delivery device VMB1. Finally, all the contacts

K1A-K6A are connected to a 115 VAC return line. As for relay K7, control means which are not shown in Figs. 1 and 2 are provided for controlling the current in each of the coils of the relays K1-K6. This control means determines which of the vend mechanisms are connected to the 115 VAC return path.

Fig. 1 illustrates a situation in which none of the vend mechanisms 20 is activated. In this state, the triac Ql is preferably off. In connection with Fig. 2, the activation of delivery device VMA2 and operation of the present invention will be illustrated.

To activate delivery device VMA2, control currents are produced so that the wiper blades of the relays Kl through K7 take the position shown in Fig. 2. In other words, wiper blade K7W connects contacts K7A and K7C, wiper blades K1W, and K3W-K6W connect contacts KIA, and K3A-K6A to contacts KIA, and K3C-K6C respectively. Further, wiper blade K2W connects contacts K2A and K2B. In a preferred arrangement, a suitable time after these control currents are produced, triac Ql is turned on by a control signal at its input 12 and power flows through delivery device VMA2 thereby activating it and causing a vend to occur so long as the delivery device VMA2 is in proper working order. After vending is completed, triac Ql is turned off and power is removed. For additional details concerning the preferred timing for switching power to the triac Ql and the relays K1-K7 see the disclosure of U.S. Application Serial No. 659,385 filed October 10, 1984 and assigned to the assignee of the present invention.

From the above discussion of Figs. 1 and 2, it can be seen that, rather than controlling a total of 2N delivery devices with 2N control elements, the present invention allows 2N delivery devices to be controlled using N+2 AC power switching control elements, or if the triac Ql is eliminated N + 1 control elements. Further, it is apparent that the present switching arrangement does not suffer from deleterious activation of delivery devices which have not been selected. As a result, substantial component cost savings are achieved. Additional details of suitable control means for controlling the switching of the AC power switching elements and of the preferred.embodiment are discussed below in the context of the discussion detailed circuit diagrams of Figs. 3A and 3B.

Figs. 3A and 3B illustrate a control circuit 100 for controlling the operation of a vending machine (not shown) having a coin mechanism (not shown) , a display (not shown) , twelve selection switches (not shown) , twelve vend motors (not shown) , twelve sold out switches (not shown) , a cash counter (not shown) and several machine function switches 170. While the typical components of a vending machine are not shown in Figs. 3A and 3B, their proper connection to control circuit 100 is readily apparent from these figures. A vending machine with control circuit 100 may have either one of two different coin mechanisms and may optionally include a dollar bill validator. Control circuit 100 includes a dual coin mechanism interface 110 and a dollar bill validator interface 150 for this purpose. Control circuit 100 also includes the necessary drive circuitry 120 to drive the triac Ql and the relays K1-K7 shown in Figs. 1 and 2 as well as Figs. 3A and 3B.

Central to control circuit 100 is a programmed microprocessor 130 which may suitably be an Intel 8049 chip. Connected to microprocessor 130 are the dual coin mechanism interface 110, a display interface 140, the dollar bill validator interface 150, a cash counter interface 160, the plurality of machine function switches 170, a soldout switch interface 180, a selection switch interface 190, a vend complete switch interface 200, the triac Ql and the relays K1-K7. Each of the interfaces listed above includes the appropriate circuitry necessary for connecting its associated element, for example, a coin me^'chanism, to the microprocessor 130. The particular dual coin mechanism interface

110 shown in Fig. 3A is for providing the vending machine operator with the option of connecting either the Mars MC5000 or the Coinco C300 coin mechanisms sold by Mars Electronics and Coinco respectively. The particular display interface 140 is for a three digit alphanumeric LED display which is used to display information such as the customer credit. The machine function switches 170 preferably include a door switch for monitoring the opening and closing of the vending machine, a free vend switch, coin dispense switches, and motor or solenoid selection switches. The dollar bill validator interface 150 shown in Fig. 3A is suitable for connection with a dollar bill validator sold by Mars Electronics. The cash counter interface 160 is suitable for connection with a 24 volt electromechanical cash counter. Finally, the particular control circuit 100 shown in Fig. 3A has interfaces 180, 190 and 200 for connection with 12 selection switches, 12 vend complete switches and 12 sold out switches whose function and connection are well known. The operation of the above elements and control circuit 100 with the exception of how they operate in conjunction to the control switching of the triac Ql and relays K1-K7 in order to activate the appropriate vend motor selected when a customer makes a selection using one of the selection switches is well known and does not constitute the subject of present invention. While Figs. 3A and 3B show one particular control circuit 100 for a particular vending machine with various features and options, other variations could be made and other options could readily be provided. For example, the dual coin mechanism interface 110 could be redesigned for other coin mechanisms, or for a single coin mechanism and microprocessor 130 could be readily reprogrammed. Other machine function switches than the switches 170 shown could be employed, and greater or lesser numbers of vend motors and consequently different numbers of selection, sold out and vend complete switches might be employed. Turning to the details of the microprocessor

130 and its control of the triac Ql and relays K1-K7, it is seen that microprocessor 130 has an output pin P24 which controls the gate current applied to the triac Ql through the connection of a buffer-driver U9 and optical-isolator U8 as well as connecting resistors and capacitors shown within the triac drive circuit block 120 in Fig. 3A. When triac Ql is turned on, power flows from a 115 AC Hot connection to contact A of relay K7. The notation [F] is used for convenience in drawing Figs. 3A and 3B and indicates a common point in the two figures. This correlation is also true for notations [A] , [B] , [C] , [D] and any other common notations.

Prior to turning on triac Ql, the microprocessor 130 must determine that a vend selection has been made by a customer, that vending conditions have been satisfied, and it must set up the relays K1-K7 properly so that the appropriate vend motor will vend when power is turned on. Initially, microprocessor 130 monitors the states of all the switches connected to the interfaces 180, 190 and 200. It does this by cyclically outputting scan pulses via pins P20-22, a serial in/parallel out shift register U10 such as a National Semiconductor 4094 chip and a 4-to-16 decoder U13 such as a National Semiconductor 74LS154 chip. When a switch is closed, the microprocessor 130 receives a return signal on the return lines 135 connected to pins Tl, Pl-0, and Pl-1 of microprocessor 130. In greater detail, switch scanning is accomplished as follows. Microprocessor 130 first causes via the serial in/parallel out shift register U10 the input pins 20, 21, 22 and 23 of the 4-to-16 decoder U13, to be all low (input pins all low 0000=code 00) . When its inputs are all low, output 0 of the 4-to-16 decoder U13 will be low and all other outputs 1-15 will be high. The low output 0 of decoder U13 is connected through diodes Dl, D13 and D25 to the first of the sold out, selection and vend complete switches respectively which are connected to interfaces 180, 190 and 200. These switches it will be recalled are located off the circuit board which contains the control circuit 100. The low signal will be returned to the circuit board, if one of said switches is closed, via the sold out switch input (SO-Input) , the selection switch input (SEL-Input) or the vend complete switch input (VC-Input) respectively. These three inputs are connected via appropriate circuitry including the three inverters, 132-134, and the return lines 135 to pins Tl, Pl-0 and Pl-1 of microprocessor 130. If by way of example, the first sold out switch is closed, input pin 1 of inverter 132 is low, its output pin 2 is high, and the microprocessor 130 interprets this high at its Tl input as an indication that the first sold out switch is closed. If the first sold out switch is not closed, input pin 1 of inverter 132 is high or approximately 5 volts as a result of its connection through the resistor network 136 to +5V DC. Consequently, its output pin 2 is low, and microprocessor 130 interprets the low at its Tl input as an indication that the first sold out switch is not closed, or, in other words, that it is open and has not been operated. The detection of whether the first selection switch and the first vend complete switch are closed or open occurs in a similar manner.

Once microprocessor 130 has determined whether any of the first group of three switches is closed or open, it then causes all but one of the inputs to the 4-to-16 decoder U13 to be low and one to be high (input pins 0001=code 01) thereby causing output 1 of 4-to-16 decoder U13 to go low and all its other outputs to go high. Microprocessor 130 now receives inputs on pins Tl, Pl-0 and Pl-1 which indicate whether the second switch in each of the three groups of switches is closed or open. This process continues until all input values 0 through 15 (codes==00 through 15) have been tried and then the cycle repeats. It should be noted that outputs 12-15 of 4-to-16 decoder U13 are used for other purposes than scanning the three groups of switches. For example, these outputs are used to determine the status of a dollar bill validator connected to the interface 150 and the machine function switches 170.

Turning to the activation of the twelve vend mechanisms connected to vend mechanism interfaces VEND MOTORS FRONT and VEND MOTORS REAR shown in Fig. 3B, it is important to note that the same 4 lines 131 that are the inputs to the 4-to-16 decoder U13 also feed vend mechanism decode circuit 210 shown in Fig. 3B. Decode circuit 210 includes a 3-to-8 decoder U7, four NAND gates U18, 2 inverters U14, and six

Exclusive-Or gates U16 and U17, which are connected to control the activation of relays K1-K7. In order to prevent the vend mechanism drive relays K1-K7 from being activated during the scanning process, an enable line ENABLE is provided. During scanning, the enable line ENABLE is kept high and the vend mechanism decode circuit 210 is disabled thereby preventing activation of the drive relays K1-K7.

Once a closed selection switch has been detected, the scan stops at the code for that selection (1st switch corresponds to code 00, 2nd switch corresponds to code 01 etc.) If the code 02 is detected for the third selection switch and all the vend conditions have been satisfied, microprocessor 130 causes enable line ENABLE to go low enabling the decoder 210. With the enable line low, the vend mechanism decoder 210 will decode the code 02 to select the proper relay switch configuration to activate the vend mechanism corresponding to the closed third selection switch. Control circuit 100 as explained above is used with a vending machine having 12 vend mechanisms. These 12 vend mechanisms can be divided into two groups of six which may be considered as being in first and second columns VEND MOTORS FRONT and VEND MOTORS REAR respectively. For purposes of continuing the discussion of the operation when the third selection switch is closed, it will be assumed that its associated vend mechanism, as well as those for the other of the first six selection motor switches are in the second column VEND MOTORS REAR, and the remaining six motors are in the first column VEND MOTORS FRONT.

The four NAND gates U18 are connected so that if the scan code is less than six a low output at pin 8 is produced. If the scan code is greater than or equal to 06, the NAND gates U18 produce a high output at pin 8. Since for the third selection switch, the scan code is 02 which is less than 06, the output at pin 8 will be low, the input to the inverter U14 connected to pin 8 will be low, the output of inverter U14 will be high, the relay driver U9 connected to U14 will prevent current from flowing through the coi,l of column select relay K7 and the wiper of relay K7 will connect contact K7A to contact K7B of relay K7 as shown in Fig. 3B. As a result, the rear column of vend motors VEND MOTORS REAR are connected to the point labeled F. When triac Ql conducts, point F and the rear vend motors are connected through the triac Ql to 115VAC Hot. Note, that for a scan code greater than 06, pin 8 of decoder U18 will produce a high output, inverter U14 will have a low output, current flows through the coil of column select relay K7, its wiper connects its contacts K7 and K7C, and the front vend motors are selected. Also, the six Exclusive-Or gates U16 and U17 operate to complement the signals from the 3 to 8 decoder U7 when the code is greater than 06 as discussed below. Since this particular circuit addresses the problem of activating two groups of six vend mechanisms, the 3-to-8 decoder U7 is connected as a 3-to-6 decoder. For input codes 00-05, outputs at lines Y0-Y5 are produced and relays K1-K6 are respectively selected. In conjunction with the operation of relay K7, the rear vend mechanisms are thereby selected. Codes greater than or equal to 06, select the front mechanisms. Code 06 produces an output at Y6 which is diode ORed back to the output Y4 so that only relay K5 is not activated as discussed further below. Code 07 produces an output at Y7 which is similarly diode ORed back to the output Y5 so that only relay K6 is not activated. Codes 08-11 result in outputs at Y0-Y3 so that relays K1-K4 are respectively not activated.

Returning to the discussion of the activation of the vend motor associated with the third selection switch, the code 02 is also decoded by 3-to-8 decoder

U7 which may suitably be a National Semiconductor

74LS138 chip so that its output pin Y2 produces a low

^■ output and its remaining output pins Y0, Yl and Y3-Y7 all produce a high output. The pins Y0-Y5 are each connected to one of the six Exclusive-Or gates U16 and U17. Outputs Y6 and Y7 are diode ORed to outputs Y4 and Y5 as discussed above. Since the code 02 is less than 06, each of the Exclusive-Or gates produces the same output signal as appears at its input since the circuit pin 8 of the NAND gates U18 produces a low output. For the code 02, current flows through the coil of relay K3 and its wiper connects the third motor to 115 V NEUT. In other words, K3's wiper moves from the position shown in Fig. 3B so that it connects contacts K3A and K3C of relay K3 so that pin R3 of the interface VEND MOTORS REAR is connected to 115V NEUT. Current does not flow in the coils of relays Kl, K2 and K4-K6 and consequently their wipers remain in the position shown in Fig. 3B. At this point, the relays K1-K7 are positioned to activate the third vend motor which is connected to the pin R3. In order to activate this motor, it is only necessary to apply power to the point F via triac Ql. Before this is done, the microprocessor 130 is programmed to check the state of the vend complete switch associated with the third motor to determine if that motor is in its normal starting or home position. If this and any other vending conditions are satisfied, the microprocessor 130 activates triac Ql and power is applied to the third motor. The vend complete switch is monitored by the microprocessor 130 to see that the vend mechanism completes a normal cycle. When it does or after a predetermined preset time, power is removed by first turning off the triac Ql and then removing the enable signal from the enable line ENABLE. After the removal of power, the microprocessor 130 resumes scanning.

Activation of vend mechanisms connected to the interface VEND MOTORS FRONT, in other words, the activation of those vend mechanisms having a code greater than 06 is similar to that explained above, but with the differences noted below. For a code greater than 06, the output of pin 8 of NAND gates U18 is high and as a consequence, current flows in the coil of relay K7, K7's wiper connects its contacts K7A and K7C, and the front column of vend mechanisms are connected to point F. At the same time, the high output at pin 8 is connected to one input of the Exclusive-Or gates U16 and U17 and it causes those gates to complement whatever signal occurs at their other inputs. For example, if there is a code 07, pin Y7 of 3-to-8 decoder U7 will produce a low output and the remaining pins Y0-Y6 will all produce high outputs. The Exclusive-Or gates U16 and U17 will complement the signal from 3-to-8 decoder U7 so that current will flow in the coils of relays K1-K5 and their wipers will connect A and C thereby preventing the activation of any motor except the one associated with the code 07 which is connected in the front group to the line Fl. Current will not flow in the coil of relay K6 so that its wiper will take the position shown in Fig. 3B thereby selecting the vend mechanism connected to interface connection Fl.

Claims

I claim:

1. An improved switching control apparatus for switching 2N alternating current (AC) powered dispensing devices in a vending machine organized in first and second groups each having N of said dispensing devices comprising:

N + 1 AC power switching elements of which a first of said N + 1 AC power switching elements is a group determining element and is connected to all 2N dispensing devices in a manner so that said first AC power switching element can control whether AC power is connected either to a common first terminal of all of the first group of dispensing devices or to a common first terminal of all of the second group of dispensing devices, and each of the remainder of said N + 1 AC power switching devices is connected to a noncommon second terminal of two dispensing devices are from each of the two groups to control whether AC power is connected to the second terminals of its corresponding dispensing devices from the first and second groups of N dispensing devices; and control means for controlling the switching of the N + 1 AC power switching elements and thereby controlling which one of the 2N dispensing devices is activated.

2. The apparatus of claim 1 further comprising an additional AC power switching element which is connected between the first of said AC power switching elements and AC power for purposes of avoiding undesirable switching transients in the N + 1 AC power switching elements when power begins to flow through an activated dispensing device.

3. The apparatus of claim 2 wherein said additional AC power switching element is controlled by said control means so that AC power is allowed to flow through said first AC power switching element only after said control means has controlled the switching of the N + 1 AC switching elements so as to select one of the dispensing devices for activation.

4. The apparatus of claim 3 wherein at least one of said dispensing devices is a vend mechanism for delivering a product, said N + 1 AC power switching elements select the vend mechanism for activation in response to the control means sensing the operation of a selection switch corresponding to the product which the vend mechanism delivers, and the control means controls said additional AC power element to allow the flow of power only if a predetermined set of vending conditions is satisfied.

5. The apparatus of claim 4 wherein the predetermined vending conditions include a determination that the product is not sold out, that the vend mechanism is in its normal rest position, and that the customer who has made the selection has deposited sufficient money to cover the cost of the selection.

6. The apparatus of claim 4 wherein one or more of the N + 1 AC switching elements comprise relays.

7. The apparatus of claim 4 wherein the control means includes a programmed microprocessor, the additional AC switching element comprises a triac, and the programmed microprocessor is connected to the gate of the triac via a buffer driver and an optical isolation circuit.

8. The apparatus of claim 4 in which the vend mechanism is an AC motor.

9. The apparatus of claim 4 in which the vend mechanism is an AC solenoid.