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.
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 sensitive bit to the shoulder 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.
These are the settings used for this project. The sensor slider is expanded
for maximum range, lights are set to turn on one at a time, corresponding to
current settings, as fast as possible.
