Wearable PCB Heater Vest
When people hear "flexible PCB designs," most people think of the crazy experiments from Carl Bugeja.
He has made tiny actuators, PCB motors, and PCB heating elements. Bugeja's latest project goes one step further by creating a wearable vest with flexible PCB heaters!
The end product is a massive flexible PCB with a human head-sized hole (30 centimeters). Copper trace patterns embedded in the polyimide material create heating elements on the wearer's front and back. In total, the traces run about 30 meters (98 feet)! In addition, magnets under a shirt attach to metal stiffeners embedded into the edge of the flex PCB to keep the vest from flapping around.
On the front are a few control electronics. The microcontroller is an ESP32 module that controls the heaters and interfaces with a temperature sensor. Also, a seven-segment LED display provides debug information, like the current temperature.
The temperature sensor is too far from the heating elements to provide an accurate temperature of the vest itself. However, its placement does offer a functional ambient measurement. Remember, ambient means inside of a shirt or jacket!
A single four-cell LiPo battery provides power to the vest. Unfortunately, the battery tends to tug on the entire vest, pulling it down from the back. The magnets give some counterforce to the brick-sized battery, but its weight is still an issue.
Bugeja admits the current design has limited practicality. For example, it takes nearly 57 watts for the vest's temperature to reach 50C. However, the energy requirements do dictate relatively large cells. One idea is to use smaller cells distributed around the vest.
That change would trade-off longer life for a little bit of flexibility. As it stands, when worn under a light sweater, the vest is nearly invisible. Of course, Bugeja is open to feedback on other ways to tackle the energy issue if you have ideas.