Sewn Circuits

Objectives

• Students will build a wearable complete circuit.

Materials

• Per Student:
  One or two 5mm LEDs
  CR2032 3V coin battery
  Sewable battery holder (source SparkFun Electricity)
  Strip of felt or fleece fabric approximately 25cm x 5 cm
  About one metre of conductive thread (source SparkFun Electricity)
  One sew-on metal snap fastener (From a sewing supplies store, these are typically about .5cm in diameter and sold in packages of 10 or more)

  CAUTION: Coin cell batteries are extremely dangerous if swallowed. This activity should be done under adult supervision and coin cell batteries should never be left where young children can come across them. 

• Per Group or Class:
  scissors
  sewing needles (and threaders, optional)
  extra materials for decoration – fabric scraps, fabric paint, etc.
  needle-nose pliers
  permanent felt marker

Key Questions

• What is a complete circuit?
• What could cause and incomplete "short circuit"?
• Where does the electric current flow? (From the battery, through the thread to the LED, from the LED through more thread to the snap, then to the second part of the snap and back to the battery.)
• Why isn’t my LED lighting up? Answer (Troubleshooting):
  a. Be sure that the LED is oriented so that the positive leg of the LED is connected to the positive side of the battery.
  b. Be sure that the thread makes good contact with the metal in the battery holder, LED and snap fastener.

What To Do

1. Remind students of the essential parts of a circuit: there must be an energy source and a path for the current to follow through the resistance. The circuit must form a circular path from the energy source (battery) through the resistance and back to the source.
2. Explain that the path in this circuit will be made of conductive thread.  The energy source is a coin battery, and the snap fastener is a switch that can open and close the circuit.
3. You could choose to have students work at their own pace, following printed instructions (photos or finished samples will be helpful).  Or you could lead the group through the project step by step.

Prepare your LED to be sewable:

1. The longer leg of the LED must be attached to the positive side of the battery.  Before you modify your LED, use a permanent marker to colour the positive leg.
2. With needle-nose pliers, bend each leg of the LED into a small loop. Trim off the excess wire.

Use conductive thread to do all the sewing:

1. Wrap the fabric around your wrist to find the best length for a bracelet.  With the fabric around your wrist, the ends should overlap by 1-2 cm.
2. Attach one side of the snap fastener by sewing it near one of the short ends of the fabric strip.
3. Do not cut the thread.  Sew a running stitch for about 5 cm.
4. Do not cut the thread.  Sew one end of the battery holder to the fabric at the end of your 5 cm of running stitch.  Make a knot and cut the thread.
5. Sew the other end of the battery holder to the fabric.  Do not cut the thread.  Identify the positive and negative terminals of the battery holder.
6. Continue in running stitch until you reach the place where you’d like to locate the LED.
7. Being very careful that the positive leg of the LED is facing the positive terminal of the battery holder, sew one loop of the LED to the fabric.  Tie a knot and cut the thread.
8. Sew the second loop of the LED to the fabric.  Do not cut the thread.
9. Continue in running stitch until you reach the other short end of the fabric.  Do not cut the thread.
10. Sew the second part of the snap fastener to the back of the fabric.

  

Test your circuit:

1. Insert a battery into the battery holder.
2. Snap the two parts of the snap fastener together. The LED should light up.

Teacher Tip: Ensure that your working space has good light. Keep all the small parts in containers so they do not drop and vanish

Extensions

• Once students have a working circuit bracelet, they can add seasonally-themed decorations. For example, they could create a flower with a light-up centre.
• Advanced sewers can try setting up series or parallel decoration circuits. Power may limit this option- it is best to explore this after a simpler project has been completed.

Other Resources

BC Hydro | Exploring Simple Circuits

BC Hydro | Exploring Series and Parallel Circuits

How Stuff Works | How Light Emitting Diodes Work

Exploratorium | Sewn Circuits