Change Purse Summary

This change purse helpfully illuminates the inside of a purse if it senses the user stretch the rim of the purse as they try to find change in frustratingly dark situations.

Operating Instructions

  1. Snap purse flap to back of purse
  2. Stretch rim of purse
  3. Use light to find exact change

Features

  • The sensor translates the user's intent into a helpful LED light
  • The snap switch leads to environmentally friendly battery power conservation
  • With exception of LED and battery, entirely soft construction
  • Use of crocheting, duplicate wiring, conductive fabrics lead to continued operation even under wear
  • Battery may be replaced

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Role of Conductive Fabrics

In this project we take advantage of textiles as optimum engineering materials that provide integrated functionality, parallel construction leading to robustness, and user friendly softness.

Circuit

Construction

The body of the purse is regular yarn crocheted in the round followed by a rim of a crocheted strip of stretch conductive yarn. The two are bound together with a crochet stitch. The rim has a resistance of 300 kilo-ohms unstretched and 50 ohms stretched. In this way it acts as a stretch sensor. The lid is sewn from conducting and non conducting fabrics with a neoprene battery holder embedded. When a conductive thread was used (as in connecting the battery terminal to the rest of the circuit), at least one other path was also sewn. This ensures that even if the purse experiences a small tear, the circuit may still survive.

Opportunities for Improvement

The movement of the lid was neglected in the design, so the exposed LED mounts may short circuit with the conductive parts of the lid when moved. This could be fixed with a simple nonconductive covering over the mounts. Also since the LED is sewn onto the same fabric as the rest of the lid, the LED may tilt up as opposed to down into the purse. One solution might be pushing the LED farther into the purse and bending it further into the purse before sewing down the mounts. Finally, the lid requires an inside hook to clasp the purse closed during transit.