The polarity test usually comes in many multimeters, polarity elétrica, refers to positive and negative . If we are going to stick to test polarity vehicular DC. We must remember that vehicles ( cars, Motorcycle, trucks, etc.) have a “negative ground” Electrical System, where the negative battery terminal is connected directly to vehicle chassis and the positive terminal provides the live wire to your electrical system.
Here is a simple circuit that often replaces the meter much more efficiently especially for those working with electricity in cars. This is a Test polarity type pen, used to analyze the electrical installation mainly Driving, bikes and trucks, Polarity with this tester, becomes much easier to check the polarity of the wires and connectors at a point where we need to know the functions of a wireless.
He also has great utility in maintaining ignition systems and electronic injection, not to mention that is very simple to make and easy to use, even in hard to reach places where a multimeter would be unfeasible. This test device brings great benefits to automotive repairers technical, installers Som, alarm, Electric glass, other technicians and hobbyists in general.
List of components:
R1 – resistor 680 Ohms por 1/8 Watts
R2 – resistor 10k Ohms por 1/8 Watts
D1 – D2 rectifier diode 1N4004 or equivalent
LED1 LED Vermelho
LED2 Led Verde
GJ1 Claw Red Alligator
Garra GJ2 preta Jacaré
This circuit is designed to operate in electric power systems 12 In, but the values of the resistors may be modified to operate with other strains such as 6 E Volts 24 Volts. Besides use in automotive electricity, Polarity this test can be used to test sources, as an indicator of logic levels in digital circuits.
The operation is simple and use is made in the following manner: The green LED illuminates when the point to be tested is positive and red LED will illuminate when the test point is negative, ie if it is connected to earth (frame) and the negative battery supply.
One suggestion mounting polarity test is shown above, but a tube of PVC 1/2 inch can also be used to house the printed circuit board. Due to simplicity of the circuit is possible to dispense with the use of PCI and if you want to miniaturize the circuit continuity testing can use SMD components. With this circuit will be so small it would fit inside of a ballpoint pen.
Source :Electronic Journal Total No. 124 July 2007