Aniomagic - examples - weight-sensitive backpack



I've been traveling a lot with my backpack, sometimes putting too much in it, which is bad for my back. Taking a cue from this weight-sensing tote on Instructables, I decided to build one using schemer. With the schemer web interface on my iPhone, I can quickly calibrate it for my needs, or make it do random flashing patterns anytime I want, without breaking out a USB cable or anything. The 3 volt felt battery holder is eye-catching too, no?


Ingredients: schemer lightboards force sensitive resistor custom sensor board felt battery holder large battery conductive thread

Preparation & Layout I wanted to have have four different lights to correspond to the weight of my backpack: green, white, blue, and red. I chose to use three lightboards and a schemer, since schemer also has a light (ID 3). If you have all five IDs of lightboards, the lowest one (ID 1) would always light-up even if the force sensor was not experiencing any load. Sometimes you want this, but for today's project, I wanted the bag to be unlit when it was on the floor, so I used IDs 2-5.
The other components of this projects are the force sensor itself, and the custom sensor board. Although you can get boards with light, temperature and touch sensors built in, for this project you need the custom sensor which allows you to connect other things - like this force sensor.

Arrangement and sewing data lines The force sensor should be attached at the shoulder where it would experience the most pressure. Then the lights cascade down, with the battery holder at the end of the line. The wiring is really simple. Unlike projects with other type of wearable boards, you only need two lines of conductive thread: data and ground, which go to all the lightboards and sensor. Basically, hook all the dots of schemer, lightboards and sensor together, in one run. This connects all their data pins.


See how you just need one piece of thread to connect all the pluses together? That's what cool about the schemer bus: simplicity.
Normally, I'd start sewing the minus connections now, but to make things easier (in this case), I sew down one of the inputs to the custom sensor. Leave a long piece of thread, since you'll connect it later to the force sensor.

Next, connect all the minus holes. On schemer, when you align it with the + sign up, the bottom 2 holes are all minus. For lightboard, the minus hole is opposite the dot hole, and for sensor, it is the bottom hole when the text is right-side-up.

Battery power Now sew down schemer's + hole to the right side of the battery holder.


Now sew down schemer's - hole to the left side of the battery holder.


Testing Insert the battery, plus side facing you. You should see schemer doing its initial sequencer pattern, unless you've reprogrammed it.



Force sensor Now it's time to hookup the force sensor. This type has less resistance as more pressure is applied to it. Choose a place where it's likely to experience the most pressure when you carry your bag. The heavier the bag, the more pressure in this spot.

Connect the two pins on the force sensor to the two side holes of the custom sensor board. It doesn't matter which one goes where. Once sewn in, you can attach the sensive bit to the soulder pad. Reprogram using the schemer interface to get your desired response. See the video at the top of the page, or go to the introductory page to learn more.