Abstract:
An electronic voltage polarity indicator that provides an easy to identify indication as to whether an electrical surface being contacted by a probe is at a positive or negative polarity. The electronic voltage polarity indicator is particularly useable with a 12 volt power source, and thus can find application in the installation of equipment in vehicles, such as automobiles.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention is directed to an electronic voltage polarity indicator that can be utilized in a vehicle environment for testing whether an electrical surface is at a positive or negative polarity, and to evaluate connectivity of low impedance.  
         [0003]     2. Discussion of the Background  
         [0004]     Instances often arise in which a person may want to determine whether an electrical surface has a positive or negative polarity. One common such instance is when installing components into a vehicle, such as an automobile. For example, if a remote vehicle starter or other automotive after market accessories are being installed into an automobile, it becomes helpful to be able to identify “dead” or “live” circuits, and instantly identified test point as being either positive or negative in polarity  
         [0005]     Other examples in which it may be desired to determine whether an electrical surface has a positive or a negative polarity is when testing door pin switches, lights, fuses, computer inputs/outputs, and distributors.  
       SUMMARY OF THE INVENTION  
       [0006]     One object of the present invention is to provide a novel electronic voltage polarity indicator for use with vehicles that can indicate whether a contacted electrical surface has a positive or negative polarity, and to evaluate connectivity of low impedance circuits.  
         [0007]     A further object of the present invention is to provide such a novel electronic voltage polarity indicator in a device that is simple and safe to use, and that provides a clear and efficient display. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:  
         [0009]      FIG. 1  shows a first embodiment of an electronic voltage polarity indicator of the present invention from an external view;  
         [0010]      FIG. 2  shows circuitry included in the electronic voltage polarity indicator of  FIG. 1 ; and  
         [0011]      FIG. 3  shows a second embodiment of an electronic voltage polarity indicator of the present invention from an external view. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to  FIG. 1  thereof, an external view of the electronic voltage polarity indicator  10  of the present invention is shown.  
         [0013]     As shown in  FIG. 1 , the electronic voltage polarity indicator  10  includes a handle portion  24 , which can be rubberized for an easy grip. Further, two connectors, such as alligator clips,  20 ,  22  are provided. Those two connectors are configured to contact to ground and to a positive power voltage source. In most vehicle environments that positive voltage source will be +12 volts, but could also be +6 volts, and variations in values of the following described circuit components can allow operation up to 50 volts nominal.  
         [0014]     One of the benefits of the present invention is that the device of the present invention is fault-tolerant with respect to the connection of the connectors  20 ,  22 . That is, with the structure in the present invention one of the connectors  20 ,  22  is connected to the voltage source and the other of the connectors is connected to ground, but it is irrelevant which one of the connectors  20 ,  22  is connected to the voltage source and which is connected to ground.  
         [0015]     The connectors  20 ,  22  can be color coded, for example to be black and red so that the red connector clip  20  can be connected to a voltage source, e.g. a +12 volt power source, and the black connector clip  22  can be connected to ground in a vehicle. However, in this case the color coding is merely for a visual effect or for providing a comfort level to a user, but is not needed because the connectors  20 ,  22  can be connected to the voltage source and ground in either order.  
         [0016]     Further, the electronic voltage polarity indicator  10  includes a probe  12  formed of a conductive metal material, two indicators  14  and  16 , and an incandescent bulb  18 . The incandescent bulb  18  provides two functions. A first function is to provide an indication when the connector clips  20 ,  22  are properly connected to a ground and a voltage source to indicate that the electronic voltage polarity indicator  10  is operating. A second function is that the incandescent bulb  18  can operate as a small flashlight to provide an illumination for the electronic voltage polarity indicator  10 , for example when it is used in a darkened area such as under a dash in an automobile. Element  18  could also take the form of other light sources, such as a white LED.  
         [0017]     Indicators  14  and  16  in a preferred embodiment are LEDs of two different colors that can provide an indication as to whether the probe element  12  is contacting an electrical surface with a positive polarity or a negative polarity. For example, the indicator  14  can be a red LED that when lit up represents that the probe element  12  is contacting a positive polarity electrical surface, and the indicator  16  can be a green LED that lights up when the probe element  12  is contacting a negative or ground electrical surface.  
         [0018]      FIG. 2  shows the internal control circuitry in the electronic voltage polarity indicator  10  that provides the desired operation and indication.  
         [0019]     As shown in  FIG. 2 , connected to the probe element  12  are the two LEDs  14 ,  16 , which are connected in parallel to each other. At a junction point J of those two LEDs  14 ,  16  a connection is made to a circuit portion including two resistors R 1 , R 2  and the incandescent bulb  18 .  
         [0020]     The circuitry in  FIG. 2  operates as follows.  
         [0021]     When the power terminal  22  is properly connected to power in the vehicle electrical system and the ground terminal  20  is properly connected to ground in the vehicle electrical system, the incandescent bulb  18  will glow to indicate those proper connections. Current will also flow through resistors R 1  and R 2  forming a Thevinin-equivalent voltage source at the junction J between the resistors R 1  and R 2 . The Thevinin voltage will be half of the automobile supply voltage, and the current may be limited by a Thevinin-equivalent impedance of 500 ohms based on the selected component values.  
         [0022]     If the probe element  12  is attached to a circuit presenting a return to ground through a low impedance, and thereby indicating the probe element  10  contacting a point with a negative polarity, light emitting diode  16  will be forward biased, and current will flow through LED  16  and LED  16  will glow to provide a green indication. The strength of the glow will be inversely related to the impedance of the ground path, and with properly selected component values anything less than 100 ohms will result in almost full brightness in the LED  16 . The red LED  14 , in this circumstance, will be reverse biased and will thereby not glow and be dark.  
         [0023]     In a contrary situation, if the probe element  12  is attached to a point that returns to, e.g., +12 volts, i.e. an element having a positive polarity, diode  14  will conduct and thereby light up providing a red indication, and the green diode  16  will be dark.  
         [0024]     If the probe element  12  connects to a point that alternates between power and ground as a voltage source, the LEDs  16  and  14  will glow alternately. If the frequency of alternation is high enough the LEDs  16  and  14  may both appear to glow steadily at the same time.  
         [0025]     Thereby, evaluating which LED  16  or  14 , or both, is glowing, i.e., whether the green LED  16  or the red LED  14  is, glowing, or if both are glowing, provides an indication to a user of the voltage polarity indicator  10  whether the point the probe element  12  is contacting a positive polarity, a negative polarity, or an alternating power source.  
         [0026]     As noted above one of the benefits in the present invention is that it is irrelevant which one of the connectors  20 ,  22  is connected to power or ground. That is, the circuit of  FIG. 2  operates properly if connector  22  is connected to ground and connector  20  is connected to the power, or vice versa. Further, one of the benefits of the circuit of  FIG. 2  is its simplicity in that it allows either connection of connectors  20 ,  22  and requires very few components.  
         [0027]     With such a circuit, and as noted above, an electronic voltage polarity indicator is provided that is simple to use, which is inexpensive to produce, which is safe to use, and which provides a simple to understand visual indication of a polarity of a contacted electrical surface.  
         [0028]     The embodiment shown in  FIG. 1  utilizes specific types of connectors  20 ,  22  to connect to ground and a power terminal, respectively. A second embodiment of the present invention shown in  FIG. 3  incorporates the same structure of the probe element of  FIG. 1 , including the circuitry of  FIG. 2 , except for the connection to a power source. In  FIG. 3  instead of utilizing two connector terminals  20 ,  22  a single power contact connector  26  to be plugged into a vehicle cigarette lighter is provided. As the proble element  10  may find particular application in use in vehicle environments, it may be helpful to utilize a power contact connector  26  for connection into a cigarette lighter. In this device when the power contact connector  26  is connected into a cigarette lighter the incandescent bulb  18  will glow. Otherwise the operation in this embodiment is the same as in the embodiment shown in  FIG. 1 .  
         [0029]     Further, in this embodiment of  FIG. 3 a  further adaptor unit including a receptacle portion  27  and power terminals  28  and  29  can also be optionally provided. By utilizing the additional adaptor unit the receptacle portion  27  can receive the power contact connector  26  and then the terminals  28  and  29  can be connected to ground and power as in the first embodiment of  FIG. 1 . That is, by utilizing the additional adaptor unit with receptacle portion  27  and terminals  28 ,  29 , the embodiment of  FIG. 3  can be utilized in the same manner as the embodiment of  FIG. 1 .  
         [0030]     It will be obvious to those skilled in the art that numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.