Pin Me

Identifying and Purchasing Resistors

written by: Terry Ligard • edited by: Lamar Stonecypher • updated: 6/29/2011

Robots use many resistors on their circuit boards. These resistors are so crucial for electronics that they would not operate without them. Therefore, it is important to know how to identify resistors if one wants to build or analyze an electronic part.

  • slide 1 of 10

    The water supply that is connected to your home comes through a rather large pipe. But the pipe leading to the shower is much smaller. The reason for this is to take up less space and deliver less water to the location. Similarly, resistors limit the flow of electricity in order to reduce waste and efficiently deliver the required amount of electricity to each part.

  • slide 2 of 10

    Obtaining a Resistor Variety Pack

    Resistors are extremely valuable, yet inexpensive, so you’ll want to acquire a variety of values. A place to start is with a ½-watt, 5% tolerance, carbon-film variety pack, as is shown below.

  • slide 3 of 10
  • slide 4 of 10
  • slide 5 of 10

    The resistor packs in the above table are sufficient for starting. The Jameco #107879 has a cabinet as well, which is always nice.

  • slide 6 of 10

    Understanding Size and Tolerance

    It is recommended to begin with the ½-watt through-hole resistors since their size makes it easier to decipher their color-coded bands. It is also fine to use the smaller ¼-watt through-hole resistors. Surface-mount resistors, however, are too small to experiment with, unless you’re experienced, so it’s best not to use them if you’re a beginner.

    A 5% tolerance indicates that a 100 Ω resistor could be low as 95 Ω or high as 105 Ω, which is accurate enough for homemade robots. One can purchase the 1% tolerance, which is more expensive, but the robot will not notice the change.

  • slide 7 of 10

    Cutting it Out

    Resistors often appear connected together with tape. This is done because they are manufactured in long reels to be fed into robotic part-placement machines. A distributor can purchase a reel and cut different lengths for custom orders.

    Peeling off the tape is an option, but residue does remain on the ends of the resistors. This residue can prevent an effective metal-to-metal connection when it comes to prototyping, and can stick to holes and sockets. A better option is to use a wire cutter tool to snip the ends off the resistors from the reel tape.

    Such a wire cutter is depicted below. It is advisable that you do not use a scissor instead, as the scissor blades will become dull and may deform.

  • slide 8 of 10
    wire cutter
  • slide 9 of 10

    Resistance and Ohms

    Ohms is the unit applied to resistance and is abbreviated with the symbol Ω. Therefore, 100 ohms is exactly the same as 100 Ω. If you can remember that resistance is like the small pipe leading to the shower head, a large Ω indicates larger resistance, or the small pipe.