Abstract:
A system for detecting the level of coins in a coin box of a vending machine includes a voltage output circuit, a coin detecting circuit, and an indication circuit. The voltage output circuit receives a DC voltage, and provides a stable reference voltage. The coin detecting circuit receives the stable reference voltage, and detects the resistance of the coins in the coin box on the basis that the aggregate of accumulated coins creates an electrical connection across the coin box in parallel with known-value resistors in the coin detecting circuit. An amplification of the reference voltage takes place and the indication circuit receives the amplified reference voltage, to indicate by display or otherwise that the coin box is filled with coins or is not yet filled with coins.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to a system to detect the level of coins in the coin boxes of vending machines. 
         [0003]    2. Description of Related Art 
         [0004]    Vending machines include coin boxes for receiving and accommodating coins. Typical vending machines cannot detect coins in the coin boxes. When the coin boxes are filled with coins, the coins may not be accepted by the coin boxes resulting the coin boxes to malfunction. 
         [0005]    Therefore, there is a need for improvement in the art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0007]      FIG. 1  is a block diagram of an embodiment of a coin-detecting system for a coin box. 
           [0008]      FIG. 2  is a circuit diagram of the coin-detecting system of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean “at least one.” 
         [0010]      FIG. 1  shows a coin-detecting system for detecting the number of coins in a coin box (coin box M) which includes a voltage output circuit  100 , a coin detecting circuit  200 , and an indication circuit  300 . 
         [0011]      FIG. 2  shows the voltage output circuit  100  which includes a first amplifier U 1 , a first variable resistor VR 1 , a first resistor R 1 , a second resistor R 2 , and a Zener diode VZ. The first amplifier U 1  includes a non-inverting input terminal, an inverting input terminal and an output terminal. The first variable resistor VR 1  includes a first terminal, a second terminal, and an adjusting terminal A first terminal of the first resistor R 1  is electrically connected to a positive terminal +VCC. A second terminal of the first resistor R 1  is electrically connected to a cathode of the Zener diode VZ. An anode of the Zener diode VZ is grounded. The first terminal of the first variable resistor VR 1  is electrically connected to the second terminal of the first resistor R 1 . The second terminal of the first variable resistor VR 1  is grounded. The adjusting terminal of the first variable resistor VR 1  is electrically connected to the non-inverting input terminal of the first amplifier U 1  via the second resistor R 2 . The inverting input terminal of the first amplifier U 1  is electrically connected to the output terminal of the first amplifier U 1 . 
         [0012]    The coin detecting circuit  200  includes a second amplifier U 2 , a single-pole multi-throw (SPMT) switch S, a third resistor R 3 , and a selection resistors R 5 -R 10 . The second amplifier U 2  includes a non-inverting input terminal, an inverting input terminal and an output terminal. The SPMT switch S includes a connection terminal and a plurality of selection terminals. The plurality of selection terminals of the SPMT switch S are electrically connected to first terminals of the selection resistors R 5 -R 10 . Second terminals of the selection resistors R 5 -R 10  are electrically connected to the output terminals of the first amplifier U 1 . The connection terminal of the SPMT switch S is electrically connected to the inverting input terminal of the second amplifier U 2 . The SPMT switch S is switched to select a first selection resistor of the selection resistors R 5 -R 10  by connecting the connection terminal and one of the plurality of selection terminals together. The non-inverting input terminal of the second amplifier U 2  is electrically connected to a negative terminal −VCC via the third resistor R 3 . The inverting input terminal and the output terminal of the second amplifier U 2  are electrically connected to two ends of the coin box M. In one embodiment, the respective resistances of the selection resistors R 5 -R 10  gradually decrease from R 5  to R 10 . A voltage on the positive terminal +VCC and the negative terminal −VCC is +9V. A current flowing through the positive terminal +VCC and the negative terminal −VCC is 12 mA. 
         [0013]    The indication circuit  300  includes a micro ampere meter P, a second variable resistor VR 2 , and a fourth resistor R 4 . The second variable resistor VR 2  includes a first terminal, a second terminal, and an adjusting terminal. A first terminal of the fourth resistor R 4  is electrically connected to the output terminal of the second amplifier U 2 . A second terminal of the fourth resistor R 4  is electrically connected to the first terminal of the second variable resistor VR 2  via the micro ampere meter P. The second terminal of the second variable resistor VR 2  is grounded. The adjusting terminal of the second variable resistor VR 2  is electrically connected to the second terminal of the second variable resistor VR 2 . 
         [0014]    In operation, the +9V DC voltage is divided by the first resistor R 1  and the first variable resistor VR 1 , and stabilized by the Zener diode VZ to generate a reference voltage. The first amplifier U 1  receives the reference voltage and outputs a stable reference voltage. A relationship between an output voltage V 1  of the first amplifier U 1  and an output voltage V 2  of the second amplifier U 2  can be calculated by the following formula: V 2 /V 1 =Rm/Rx. In one embodiment, Rm is an overall resistance of the coin box M, and Rx is a resistance of one of the selection resistors R 5 -R 10 . A value of the current displayed on the micro ampere meter P is the quantity of current passing through the fourth resistor R 4  and the second variable resistor VR 2 . The value of the current displayed on the micro ampere meter P is proportional to the output voltage V 2  of the second amplifier U 2 . When coins are dropped into the coin box M, the coins are electrically connected in parallel with the coin box M. Thus the overall resistance of the coin box M decreases as a number of the coins put into the coin box M increases. 
         [0015]    According to the above formula, the output voltage V 2  of the second amplifier U 2  is proportional to the resistance of the coin box M, and the output voltage V 2  of the second amplifier U 2  is inversely proportional to the resistance of one of the selection resistors R 5 -R 10 . When the coin box M is completely filled with coins, the resistance of the coin box M has a minimum value, and the output voltage V 2  of the second amplifier U 2  has a minimum value when the resistance of one of the selection resistors R 5 -R 10  is fixed. Therefore, the value of the current displayed on the micro ampere meter P also has a minimum value. 
         [0016]    When the coin box M is not filled with coins, the overall resistance of the coin box M is greater than the minimum value of the resistance Rm, and the output voltage V 2  of the second amplifier U 2  is greater than the minimum value of the output voltage V 2  when the resistance of one of the selection resistors R 5 -R 10  is fixed. Therefore, the value of the current displayed on the micro ampere meter P is greater than the minimum value of the current value. The value of the current displayed on the micro ampere meter P thus indicates whether the coin box M is filled with coins or not filled with coins. 
         [0017]    In one embodiment, the SPMT switch S can select one of the selection resistors R 5 -R 10  according to a manufactured volume of the coin box M. When the manufactured volume of the coin box M increases, the coin box M can be filled with more coins, and the resistance Rm of the coin box M is smaller than the minimum value of the resistance. The output voltage V 2  of the second amplifier U 2  is smaller than the minimum value of the output voltage V 2 . Therefore, the value of the current displayed on the micro ampere meter P is smaller than the minimum value of the current value, and the value of the current will not be displayed on the micro ampere meter P. The SPMT switch S is switchable to select a second selection resistor of the selection resistors R 5 -R 10  which having a resistance smaller than a resistance of the first selection resistor. The resistance Rx of the second selection resistor is merely decreased to increase the output voltage V 2  of the second amplifier U 2  and the value of the current displayed on the micro ampere meter P. Therefore, the value of the current being displayed on the micro ampere meter P, to indicate that the coin box M is full, can be adjusted to suit different manufactured sizes of coin box. Similarly, when the manufactured volume of the coin box M decreases, the SPMT switch S is switched to select a third resistor of selection resistors R 5 -R 10  having a resistance greater than the resistance of the first selection resistor. 
         [0018]    Even though numerous characteristics and advantages of the present disclosure have been set forth in the foregoing description, together with details of the structure and function of the disclosure, the disclosure is illustrative only, and changes may be made in detail, especially in the matters of shape, size, and the arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.