A solid state desktop coaster that actively heats or cools any standard mug, glass or can, with no proprietary drinkware. One Peltier module, closed loop control, and a safety architecture designed for unattended desk use.
Existing options split into two bad camps: proprietary heated mugs that lock you into their drinkware, and cheap USB warmers with no temperature regulation at all. The interesting problem sits in between.
One compact device that both heats and cools, works with whatever cup is already on the desk, and can be trusted to run unattended. The last of those is the hard one: a heater left alone on a desk is a fire risk if nothing independent is watching it.
A thermoelectric module does both jobs: drive current one way and the top plate cools, reverse it and the plate heats. The TEC1-12703 sits between an aluminium top plate and a finned heatsink with a blower carrying away waste heat.
An NTC thermistor at the plate closes the loop, targeting about 2 degrees Fahrenheit around setpoint, with the module driven through a DRV8871 H-bridge so firmware controls both power and polarity.
Safety is layered the way my lab test rig is: the control loop regulates, and separate firmware cutoffs watch for thermal runaway independently of it, so an unattended fault shuts the device down.
Before integrating any control loop I bench tested the bare thermal stack against a lab supply with K-type thermocouples on both faces. At 12 V the cold face held 10.7 to 12 degrees C with the heatsink at 53 to 56, reaching equilibrium in about five minutes.
A voltage sweep mapped cold face temperature against input power to find the efficient operating window. Swapping the heatsink's stock adhesive pad for proper thermal paste measurably improved performance: the interfaces matter as much as the module.