How to Construct a Variable Inductor

Written by jason thompson
  • Share
  • Tweet
  • Share
  • Email

A variable inductor is a must-have component in any electronic hobbyist's tool kit. Made out of a coil of wire wound around an iron core to increase the strength of the magnetic field generated, inductors tune radios, change voltage levels, alter currents and more. When they are made as variable inductors, they change their inductance value, making them even more useful. A single variable inductor can do the jobs of many different fixed inductors. Easily make one at home out of common parts.

Skill level:

Things you need

  • Cardboard tube from roll of paper towels
  • Electrical tape
  • Spool of 28 gauge magnet wire
  • Wire cutters
  • Emery board
  • Iron bar, almost as wide as the tube is on the inside, longer than half the length of the cardboard tube

Show MoreHide


  1. 1

    Tape the magnet wire to the left end of the cardboard tube with the electrical tape. Tape it several inches down from one end of the wire.

  2. 2

    Wrap seven hundred loops of the wire around the tube, always wrapping left to right. Never wrap the wire back and forth, as this will weaken your inductor. Keep each loop as close to the others as you can. Cover most of the tube with wire this way.

  3. 3

    Tape the wire to the tube immediately next to the end of the coil. Cut the wire from the spool using the wire cutters, several inches from where it is taped.

  4. 4

    Use the emery board to sand one inch of the enamel insulation from each of the wires coming from the coil you wound.

  5. 5

    Slide the iron bar into the end of the tube with the wire on it. Align the iron bar inside the cardboard tube do that every loop of the coil has iron inside it. Your variable inductor is now complete and in the "maximum" position.

  6. 6

    Connect the wire ends of the coil, which serve as the leads to your inductor to the circuits in the same manner that you would the leads of any store-bought inductor.

Tips and warnings

  • To vary its inductance, slide the bar down the tube so that some of the loops of the coil no longer have iron in the middle, only air. This will lower the inductance of the coil, because the easily magnetised iron is under fewer coils.

Don't Miss

  • All types
  • Articles
  • Slideshows
  • Videos
  • Most relevant
  • Most popular
  • Most recent

No articles available

No slideshows available

No videos available

By using the site, you consent to the use of cookies. For more information, please see our Cookie policy.