RESISTOR BASICS

Resistors, like diodes and relays, are another of the electronic parts that should have a section in the installer's parts bin. They have become a necessity for the mobile electronics installer, whether it be for door locks, timing circuits, remote starts, or just to discharge a stiffening capacitor.

Resistors "resist" the flow of electrical current. The higher the value of resistance (measured in ohms) the lower the current will be.

Resistors are color coded. To read the color code of a common 4 band 1K ohm resistor with a 5% tolerance, start at the opposite side of the GOLD tolerance band and read from left to right. Write down the corresponding number from the color chart below for the 1st color band (BROWN). To the right of that number, write the corresponding number for the 2nd band (BLACK) . Now multiply that number (you should have 10) by the corresponding multiplier number of the 3rd band (RED)(100).

BLACK                  0

BROWN                 1

RED                        2

ORANGE                3

YELLOW                4

GREEN                   5

BLUE                      6

VIOLET                  7

GRAY                     8

WHITE                    9

 

Tolerance Colour
±1% brown
±2% red
±5% gold
±10% silver

          

                                   

Resistors are used with transducers to make sensor subsystems. Transducers are electronic components which convert energy from one form into another, where one of the forms of energy is electrical. A light dependent resistor, or LDR, is an example of an input transducer. Changes in the brightness of the light shining onto the surface of the LDR result in changes in its resistance. As will be explained later, an input transducer is most often connected along with a resistor to to make a circuit called a potential divider. In this case, the output of the potential divider will be a voltage signal which reflects changes in illumination.

                 Types of resistors

        Carbon film resistors
 

    This is the most general purpose, cheap resistor. Usually the tolerance of the resistance value is ±5%. Power ratings of 1/8W, 1/4W and 1/2W are frequently used.
    Carbon film resistors have a disadvantage; they tend to be electrically noisy. Metal film resistors are recommended for use in analog circuits. However, I have never experienced any problems with this noise.
     
       Variable Resistors
 

    There are two general ways in which variable resistors are used. One is the variable resistor which value is easily changed, like the volume adjustment of Radio. The other is semi-fixed resistor that is not meant to be adjusted by anyone but a technician. It is used to adjust the operating condition of the circuit by the technician. Semi-fixed resistors are used to compensate for the inaccuracies of the resistors, and to fine-tune a circuit. The rotation angle of the variable resistor is usually about 300 degrees. Some variable resistors must be turned many times to use the whole range of resistance they offer. This allows for very precise adjustments of their value. These are called "Potentiometers" or "Trimmer Potentiometers."
     

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