Author Archive

Final Project Report – A Weight-Sensing Tote Bag

Posted in 11. Project Final Reports on December 14, 2009 by Mark Leung

My project was a weight sensing bag. It helps people who carry a lot in their bags and improves on scales by providing constant ambient feedback and an automatic warning alert for excess weight.

How it works
It works by using a force sensitive resistor to measure how much the strap is pressing on the wearer’s shoulder, and using the value to control how fast LEDs pulsate, or how many LEDs have lit up (when a switch is pressed), giving the user feedback. When the wearer wears excessive weight (currently calibrated at approximately 10-11 pounds), the LEDs blink rapidly to warn the wearer. The entire apparatus is powered by an AAA battery and controlled by a Lilypad Arduino, which is attached to components by conductive thread sewn into the surface of the bag.

Design process is described in the Instructable

Arduino Sketch: ReadInput


Ergonomic Tote Bag

Posted in 9. Project Proposals on November 7, 2009 by Mark Leung

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
1 Needle
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

HW8 – State machine

Posted in 8. Finite State Machines on October 29, 2009 by Mark Leung

I used a servo motor, IR sensor and switch to create a machine that takes an object and throws it over a table.

State 1 waits for an object to trigger the IR sensor and moves the servo to load an object.
State 2 waits for a switch and throws the object.
State 3 waits 3 seconds then returns the servo to its State 1 position.


Circuit Diagram
Circuit Diagram

Arduino Sketch: HW8

Homework 7 – Playoffs

Posted in 7. A Mechanical Automaton, Uncategorized on October 17, 2009 by Mark Leung

Since it’s playoff time, I decided to make a tribute to my least favourite baseball player. I built an automaton out of cardboard, foamcore, doweling, a straw, paper, and tape.

Entire Automaton

Two offset cams were cut out of cardboard (for up and down, side to side motion) and skewered with the doweling. The cams were stabilised with pieces of foam on either side, and the skewer was stuck through the sides of a cardboard box.

The cam follower was built out of foamcore, with a layer of foam underneath for friction, and a dowel.
Cam Follower

The cam follower’s doweling was inserted through the top of the box, and stabilised with a plastic straw, and the cams’ doweling went through the sides of the box. Tape was used to create friction between the doweling and the cams.


A dowel and cardboard handle was attached to the side doweling to create a handle for the automaton.


A paper hand was taped to the dowel attached to the cam follower, and a paper face with cardboard inside was taped next to it.

Homework 6

Posted in 6 Form & Motion on October 8, 2009 by Mark Leung


Arduino Sketch:

Traffic Stop

DC Motor

Circuit Diagram
Traffic Stop
DC Motor

Treasure Hunt

Posted in 5. Treasure Hunt on October 1, 2009 by Mark Leung

Flex Sensor – 12.95
Fabric/stretch sensor – 20.95
Electroluminescent “wire” (EL-wire) – $5.99
Alcohol sensor – $4.50
Solenoid – 18.95
Linear actuator – 49.95
Fiber optic cable – $31
Tiny potentiometer – $2.99
Conductive fabric – Pure copper polyester taffeta fabric – 10.99 per linear foot
Thermochromic paint/dye – $44.99
Nitinol / shape memory alloy wire – $8.52
Conductive paint – 17.95
Neodymium magnets – $3.98
Copper tape / copper foil – $2.95
Tilt sensor – $2.00
Peltier Junction – $49.99

<a href=””>Electroluminescent “wire” (EL-wire)</a> – $5.99
<a href=””>Conductive fabric – Pure copper polyester taffeta fabric</a> – 10.99 per linear foot
<a href=”″>Nitinol / shape memory alloy wire</a> – $8.52
Interesting Item

Interesting Item
thermochromic putty – 8.95

Homework 4

Posted in 4. Analog Input-Output on September 24, 2009 by Mark Leung




Arduino Sketch: HW4