Some Quick LED and Circuit Basics

Time to build the circuit and add the LED(s)! Keep these things in mind as you go:

  • A circuit is a path for electricity to travel along. The current will only flow when the circuit is closed, meaning the path goes all the way from the positive side of the battery (marked with a "+") to the negative side without a break. That's why the LED will only turn on when the wristband circuit is closed.
  • Since you will insert the battery with the positive side facing up, the top piece of tape -- which wraps around to connect to the top of the battery -- is the positive trace.
  • The bottom piece of tape -- which is touching the negative side of the battery -- is the negative trace.
  • By running the positive and negative traces in parallel lines next to each other, you can create a parallel circuit. In a parallel circuit, every LED is connected directly to the battery. This allows you to run several LEDs off of one 3-volt battery.
  • Like other kinds of components, LEDs have a positive and a negative side. In addition, LEDs have polarity, which means they only work when the positive side is connected to the positive side of the battery, and the negative side is connected to the negative side. Make sure you connect your LEDs in the right direction!
  • Avoid creating a short circuit, an accidental connection between two parts of the circuit. Make sure the positive and negative traces cannot touch unless you close the circuit.
Never close the circuit with only a battery connected to it. If there is no LED, you will short-circuit the battery, causing it to heat up and burn out quickly. A hot battery can be a fire hazard!
To protect the battery from a short circuit, cover the ends with electrical tape as shown on the Add the Battery page.

Create the Traces with Tape

For the first trace, take a strip of conductive tape at least half as long as the felt band. Lay it out above the bottom slit so it goes across the spot where the battery fits and ends past the middle of the felt.


Tip: To attach the tape neatly, peel off just a little of the backing paper to start. Press the adhesive securely onto the felt. Then keep peeling the paper off slowly you press the rest of the tape onto the felt.

 

For the second trace, take another strip of conductive tape long enough to go from about the middle of the band to the other end and over onto the back for about 1 inch.

Be sure to leave a gap of about 1/4 inch between the two pieces of tape!

This guide was first published on Nov 13, 2018. It was last updated on Nov 13, 2018.

This page (Build the Soft Circuit) was last updated on Nov 02, 2020.