My project is a weight sensing tote bag. It aims to help people avoid carrying excessive loads on their shoulders. I changed the bag type from a backpack to a tote for several reasons. There is much more flexibility in placing an interface on a tote’s entire surface as opposed to a backpack where only the straps are practical. Tote bags, being one shouldered bags, are more damaging to the body than a backpack of the same weight.
Furthermore, there has been a boom in cloth totes recently with the banning of plastic bags in supermarkets for environmental reasons in several countries such as Hong Kong. Tote bags have begun turning into fashion statements as they become more common, and it is not inconceivable that people would be willing to spend money on a bag with integrated electronics.
A key usage for this tote is shopping, whether for groceries or other tasks. Shopping for groceries creates a heavy load on the shoulder, and there is uncertainty with respect to the weight of goods you purchase, making it easy to buy too many goods. This device would be useful for reminding shoppers not to buy too much at once.
In my design, there would be a force sensitive resistor in the shoulder strap of the bag, connected to the Arduino with conductive thread. The Arduino would sit in the bag with its power supply and a vibration motor. It would also be connected to LEDs and switches that would be sewn on the exterior of the bag. The switches would be used to select the threshold of weight, and the LEDs would show the threshold, either by showing the colour, or by using a pattern of LEDs. This way people with different sensitivities to shoulder strain could adjust their weight limit accordingly.
When the pressure on the shoulder strap exceeds the specified amount, the vibration motor would activate for a certain period, to alert the wearer, but would eventually stop. After that, the LEDs would be activated, to provide a less annoying means of feedback to the wearer.
1 Lilypad vibration motor
1 Lilypad arduino
1 Lilypad breakout box
1 Lilypad power supply
2 Lilypad button switches
1 Lilypad tri-color LED
1 spool Conductive Thread
1 spool Regular Thread
2 Force sensitive resistors
I think the hardest part would be learning to create fabric based circuits. It’s totally different from using wires to create circuits, and would probably require more forethought in terms of how to run the threads since modification will be more difficult than with a regular breadboard. I will probably mock it up on a regular
Also, dealing with the FSR might be demanding. This usage only requires an approximate indicator of weight (within say 2 or 3 pounds), so precision is not a huge issue, but walking creates a fluctuating force on the strap, so it will be necessary to measure the average of force over several seconds to smooth out the input signal. This will require some tinkering with the programming.
Things I can add: Make the LEDs function outside of as a weight indicator. They could fluctuate as you walked, or other interesting patterns related to the FSR. This would enhance the fashion statement element of the bag in addition to the ergonomic element.
Week 1: test and calibrate force sensor, solve fluctuations in sensor readings with code. Begin prototype with regular arduino.
Week 2: Finish prototype with regular arduino. Design and begin learning fabric circuits.
Week 3: Prototype fabric circuit to match regular Arduino’s, begin documentation, begin extra features if there is time
Week 4: Refine fabric circuit, finish extra features if there is time, finish documentation