Being constantly disappointed by the heated socks I've bought I decided to make my own controlled by an arduino and powered by 2-4S lipo. The socks are cheap ones sold on eBay and the idea is to have the battery and control unit tucked away in my jacket with cables to each sock. Obvious downsides in having cables running through my pants but the upsides more then make up for it.
The control unit has a momentary flip-switch ON-OFF-ON and a number of LEDs which shows if it is powered, level of power output and battery status. A N-level MOSFET handles the power output and it it gets too hot the lid can be made of 2mm aluminium acting as a heat sink.
During testing I realized that mopre power then 25W is burning up my feet so I made that the max level for fully charged 3- & 4S batteries
Code and schematics: https://www.tinkercad.com/things/j0S4ZQJT6rA
NOTE: Tinkercad only has Arduino UNO which differs from the Pro Micro I use in this project. In the code the only difference is the buzzer pin. Uncomment/comment relevant lines in the beginning of the code for the buzzer pin.
8 pcs 5x2mm flat LEDs
8 pcs suitable resistors for the LEDs (I use 150)
1 pcs Logic level (N) MOSFET (I use FQP30N06L)
1 pcs resistor for MOSFET, between Gate & Source (I use 10k)
1 pcs resistor for MOSFET between digital pin and Gate
2 pcs resistors for a voltage divider (750 and 2k)
1 pcs Arduino Pro Micro (Sparkfun or clone)
1 pga Polulu 5V 500mA buck regulator
1 pcs 5V buzzer
1 pcs Momentary flip switch ON-OFF-ON
1 pcs resistor for switch (I use 200)
1 pair Cheap heated socks (I got mine on eBay for ~10USD).
NOTE: The schematics and code on TinkerCAD (link below) is default for Arduino UNO, make sure to uncomment/comment which pin to use for the buzzer before uploading it to the Pro Micro board.
Schematics and code: https://www.tinkercad.com/things/j0S4ZQJT6rA
EDIT 190129: Added a version with one larger hole for cables instead of two small.