Initial report by Joo Youn Paek, 28, March, 2006

To detect the behavior of using zippers Ė sliding along between two fabrics to open and close something - I created sensors with zippers.

Applicaiton of Zippers in General

Zippers are common tool in every day lives. Simply do they open and close two parts of fabric. They are mostly attached to clothes, bags and covers. It is an easy tool for any object - couch, notebook, camera and human - to change its skin.

Physical Characteristic of Zippers

There are three different types in the market in terms of materials: brass, nickel, aluminum and plastic. I went to Panda international (38th st between 7th and 8th ave, New York) to see all kinds of zippers and bought the biggest size of each. (So it can be easier to work for prototyping.) I checked the conduction. Bass was most conductive followed by nickel and aluminum. Also, I checked continuity if teeth are touching each other when it is closed. They donít connect enough to work as a switch just by the zipper itself. Observing the physical object really tells me how to add the function to it. Let's see the structure of a zipper.

Other Materials

I bought conductive thread from this Canadian site. It is originally for fixing lame. The site tells you how to use as well. Zigzag stich is recomended to assure the continuity. From My experience just one line of conductive thread is not reliable. Because thread is easy to tear out during sewing and even after use. So when hand sewing two line is better to secure the continuity.
  • Resisters
I used 45 peices of 220 ohm resisters to make 10k ohm variable resister. By banding the wire of the resister I made hook to sew it through. If you want even less volume than normal resister, you can use tiny surface mount resister. To tie with the thread, solder conductive beads at the both end of the resister.

Sensor Schematics

I made two different types of input with zipper sensor - analog and digital. My initial thought was to make liner analog potentiometer by using the slider as connecter. Yet during producing, I begin to think any handmade physical device might be not reliable to use as sensor. Conductive thread might create some iragualer resistence. Stiching unit is not always exactlly same so that the value change would not follow exactlly as the movment of the slider. Thus I planed to make an analog and a digital zipper sensor with in same length so that both can be compared with the motion reading. For the analog I used plastic zipper to secure disconnection between both sides. And for the digital I used nickel zipper because some of the teeth will function as contact point of switches.

Analog Sensor:

My first step was to choose an analog in sensor as resference to new zipper sensor. I chose the most common turning nob type 10k ohm potentiometer for the reference. Since it is 10k ohme variable resister, I design to have 46 pieces of 220 ohm resister in line to have detailed value in proper length of zipper. It ended to be about 24 inch.
  • Simple Schematics
When the zipper is applied to jackets or shirts, pull down resister is needed next to the signal thread. Because when both sides of the zipper are totally separated, the signal thread will loose the connection to the ground and give random value.
  • How the thread circuit is made on the zipper
This picture shows how resisters are attached to the zipper and how the slider is closing the thread circuit
  • Two different ways of electricity flow through the sensor :
Depending on the application, the direction of the highest value can be controlled by switchng power and ground.
  • How the slider connects two stich line :
The slider itself has the perfect structure to connect two stich lines sewed in the opposite sides. Though the zipper teeth are made out of plastic, usually sliders are made of painted nickel. So by sanding the inside part of the slider body where it holds the tape, slider can tranfer the electricity from one stich to the opposite side one. Red marks below are connecting parts between the thread and the slider.

Digital Sensor

The method of digital zipper sensor is multiple switch. The metal zipper - copper, nickel and aluminum zipper - has appropreate structure for liner multiple switch. My initiate thought was that when metal zippers are closed it will have continuety from top to the bottom. But the fact was not. Each teeth are separated from each other unless the tape is bent more than 120 degree angle in vertical. This means each teeth can transfer different datas. So if I tie the conductive thread to touch the opposite side tooth when the zipper is closed, I can make a single switch. And making this switch in regular distance in the zipper will create liner multiple switch.
  • Simple Schematics
  • How the thread circuit is made on the zipper

Building Process

  • Step 1. Pre-prototype on the breadboard using conductive thread
  • Step 2. Sand the body of the slider to clear the surface
  • Step 3. Sew the tape with conductive tread to create circuit

Board Schematics

Code Sample

Typical Behavior

  • Comparison between Analog In and Digital In Zipper Sensor
 !Analog Sensor!Digital Sensor
!Sensor Circuitcomplexsimple
!Board Circuitsimplecomplex
!Sensing Accuracyreliablereliable
!Sliding FeelSmoothStiff
One tricky thing for metal zippers: Although the zipper is opened, when a tooth touches the tooth from the other side, the switch will be turned on.
Above all, the choice between analog and digital depends on your application.

Application Notes

Making a musical instrument with clothes so that performers can play music by sliding the zipper on their clothes. Wearing and striping during playing the music would be interesting as well.

Another is lighting inside of womanís handbag. Many women carry more than three to five different things in their handbags. And most handbags are not designed to separate and organize different objects. Consequently, we can easily see them wasting their time to find things from it. Illuminating inside as the user opens the bag will make it easy to see inside.