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About Soft Circuits

Prototyping with Alligator Clips

As you can imagine, sewing together a soft circuit takes a good deal of time an effort. For this reason we recommend that you prototype your circuit first using alligator clips. Leah¬†Buechley¬†has a great tutorial on how to make a coaster for your Lilypad components so that the clips don’t slip from their connections.

Insulation

Unlike regular protyping wire, like hook up wire or wrap wire, conductive fabrics and threads are not insulated! This means that it’s crucial that you consider how your circuit is laid out and how it will be used.

For layout, the ideal scenario is that the lines of your circuit will never cross. Obviously, there are times when this can’t be avoided, but try to design your circuit so there are as few cross-overs as possible. When you do need to cross a line of conductive thread or fabric over another, there are several options:

  • Insulate using a piece of fabric. Iron-on patches that you buy at the store can be a quick and easy solution for this.
  • Use fabric glue or paint to insulate a trace. Leah Buechley recommends puffy paint as a good insulator.

In terms of insulation, it’s also important to consider how this circuit will be used and handled. If it’s going to lay completely flat all the time, there’s really no need to worry about insulation other than those spots where your traces cross. But if it’s something that’s going to be worn, handled, or crumpled up, it’s possible that two of those traces might accidentally come into contact with each other. In situations like this, it’s smart to insulate the whole circuit, perhaps by covering it with another piece of fabric.

Resistance

Conductive threads are often highly resistive. This means that even over the distance as small few inches, the amount of current can be greatly reduced. In a situation when your using a component that only needs a small amount of current (like an LED), this isn’t really an issue. But it does matter when you are using something that needs a larger amount of current, such as a motor or an… XBee! That’s right, a regular XBee draws 50 mA of current and an XBee Pro can draw up to 215mA. Most types of conductive thread don’t work well in this scenario. We recommend using strips of conductive fabric between your battery and the Lilypad XBee to ensure that you’re getting plenty of current. The other solution is to place your Lilypad and power source VERY close together and to triple up your conductive thread, but we usually go with the fabric solution just to be safe.