A "Hello World" (or, rather, "Eat Me") fabric PCB
By Angela, Nadia, Rizal, and Yang
Why "Eat me"? We initially wanted to program five LED lights to flash the message "Hello world" (in addition to other messages, such as "New textiles" and our names) using Morse code. However, using a microcontroller with only 1 kB of in-system programmable flash, we were limited to short messages with minimal Morse code digits! (For example, "E" and "T" are only one digit each, while "H" and "L" have four digits each.)
Primary (electrical) system components
+An Amtel ATtiny13 microcontroller: maximum 5 outputs, 1kB in-system programmable flash
+5 LED lights
+One resistor per LED
+A battery
+Conductive textile materials: thread, fabric
System overview
We have constructed a messenger bag that has decorative lights that flash when a metal snap on the side of the bag is closed. For the aesthetics, the bag has five pairs of flowers and bees. Each flower has an LED light in the center of it, and each bee is a resistor; each LED (flower) is connected to its respective resistor (bee) via conductive thread. Each of the flowers flashes its own letter to spell out "Eat me" for the bees! Note: In the image of the bag shown below, only four flowers can be seen, as one is on the back of the bag.
Circuit-wise, our system has five outputs and one input:
Outputs: 5 LED lights (one for each of the microncontroller's independent outputs).
Input: A switch that either completes or opens the circuit. Here, the switch is a metal snap, whose two halves are electrically connected--via conductive thread--to two open ends of the circuit that connect the battery, the microcontroller, and each LED-resistor pair.
Concept iteration & Design Process
To arrive at the final design described above, we had several significant design iterations due to various issues that came up during the construction process:
1. We had several issues with the PCB. In terms of the microcontroller sizing, there are three sets of dimensions listed by the manufacturer (Minimum, Normal and Maximum). When we initially designed the PCB layout (shown below under "Plan A"), we used the "Normal" dimensions. After laser-cutting the initial PCB layout, we realized that the pin locations did not match those of our microcontroller, so we might have used the incorrect dimensions. Note: Under "Plan A", a map of Cambridge, MA is shown under the PCB layout; one of our initial concepts for the project was to make an interactive map.
2. Also for the initial PCB layout (shown in "Plan A"), when we laser-cut the materials we put the Zelt fabric upside-down without flipping the image we were cutting. Normally this would not be too much of an issue, but we planned to have the Zelt be part of the aesthetics of our project, so it had to be right-side up.
Because of these setbacks, we decided to create a very simple PCB by stretching out the microcontroller pins and sewing (instead of soldering) them into the "board." Going with Plan B, our final PCB design, integrated into a functional messenger bag, is shown below! The code that causes our LEDs to spell out "Eat me" is shown on the right of the images of the bag.
Results & experience
We are very pleased with how beautiful and robust (both electrically and as functional accessory) our project is! In this first video, our messenger bag is shown in dim lighting so that the flashing LEDs can seen. The five lights (again, only four can be seen because the fifth one is on the back of the bag), flash in order to spell out "Eat me" using Morse code. This second video shows the bag completely in the dark so that only the lights can be seen. Some of the light coming from the LEDs is a little subtle, possibly due to a weakened LED or non-ideal electrical connection.
In addition to the aforementioned technical issues that resulted in multiple design iterations, our experience with this project made us realize that things almost always don't work as well as they do on paper! We learned to be patient and persistent in testing our microcontroller, especially because none of us are particularly strong in electronics or programming. Regardless, we really appreciated this opportunity to improve our skills and to work on unfamiliar aspects of the project!
Here are additional images of our project!