Customize Your Cosy Toesies with Zachary Murtishi's PWM-Driven Heated Sock Controller
This Microchip ATmega328P-driven PWM controller turns simple on/off heated socks into the temperature of your choosing.
Maker Zachary Murtishi has designed an add-on board that makes a pair of heated socks that little bit more usable — by delivering adjustable heat control via pulse-width modulation (PWM).
"This project uses a [Microchip] ATmega328P and a bunch of other basic/promotional extended SMD [Surface Mount Device] components from JLCPCB to implement a basic PWM controller to manage the temperature of a heated sock," Murtishi explains, having received the socks as a gift. "The device is powered from a wall wart or other DC supply, which is used to power the board's electronics and the heated sock itself."
Heated socks work in the same way as an electric blanket, using a resistive load spread through the fabric to turn electricity into heat. Like most electric blankets, they're simple devices: the heat is either on, or it's off. Murtishi wasn't happy with that, so set about creating a temperature controller with a little more nuance.
"I tested the idea I had in mind using an Arduino UNO R3 feeding a [Texas Instruments] ULN2003A [Darlington transistor array] with a PWM input to control the average power dissipated by the sock," Murtishi explains. "I used a cheap switching power supply to source a 6.1V DC voltage to the sock and the USB-powered Arduino to generate the PWM inputs to the ULN2003 performing low-side switching on the sock. Why 6.1V? It won't lead to excessive current through the ULN2003A and lets me test the PWM control idea."
Having successfully proven the concept, Murtishi set about designing a custom circuit board for the project — driven by the low-cost Microchip ATMega3280P. An input jack takes power from a DC wall-wart adapter, while a smaller output jack connects to the heated socks. A potentiometer at the top of the board adjusts the duty cycle of the PWM controller, increasing or decreasing the temperature of the socks at-will.
More information on the project is available on Hackaday.io, along with schematics, PCB fabrication files, and the source code under an unspecified license.