Prototype 4: Materials as Sensors

Weight-Sensitive Canvas Bag

Key Image



I embroidered this tote bag using alpaca yarn, my favourite fibre.



In this project the canvas bag lights sewed at the front of the canvas bag indicate the weight being carried inside the bag. There is a scale of lights depending on the weight placed inside. The first light turns on to indicate there is something in the bag, the second light will turn on when more weight is added, and the third light indicates the maximum weight has been reached.

Sensor was made with two layers of aluminum foil separated by a layer of velostat. I glued aluminum foil to velostat in the four corners on each side and covered this with a sleeve made of non-conductive fabric. Sensor’s input goes through pin A2 and output to LED lights goes through pins A1, A3 and A7.

The sensor is placed at the bottom of the canvas bag, so when some weight is placed on the bag and a person lifts it, LED lights will go on depending on the weight of the bag.

Parts and Materials List


  • Adafruit Circuit Playground Express
  • Resistor
  • Sewable LED lights
  • Li-Ion Poly 1200mAh battery


  • Aluminum foil
  • Velostat
  • Non-conductive fabric
  • Alligator-clip jumper wires
  • Conductive thread
  • Non-conductive thread
  • Canvas bag embroidered with Alpaca yarn


  • Scissors
  • Glue gun

Circuit Diagram



See code here.


wa4_step01 Step 1
Cut a piece of velostat and two pieces of aluminum foil. Fold aluminum foil to match the size of the velostat, leaving a narrow tip out for connectors.
wa4_step02 Step 2
Aluminum foil was glued to each side of the velostat in the four corners, so glue does interfere with flow of electricity between the two layers of aluminum foil.
wa4_step04 Step 3
Sensor is covered with non-conductive fabric to isolate the sensor and avoid short circuits. Fabric is thick, so it provides some cushion too. Fabric is stitched on the sides to make a sleeve that will cover the sensor.
wa4_step03 Step 4
Next is to fix the Circuit Playground Express and connect LED lights. I used both conductive and non-conductive thread.
wa4_step05 Step 5
The Circuit Playground Express board is stitched at the top of the bag using non-conductive thread.
Step 6
Lights are stitched and connected to the corresponding “pins” in the Circuit Playground Express board using conductive thread.
Step 7
Sensor is placed at the bottom of the canvas bag and connected using alligator-clip jumper wires. Also, battery is connected to the Circuit Playground Express board.



Leave a Reply