$τ$HK: a modular housekeeping system for cryostats and balloon payloads

$τ$HK is a versatile experiment housekeeping (HK) system designed to perform cryogenic temperature readout and heater control on the upcoming Taurus balloon experiment. $τ$HK, more broadly, is also suitable for ambient-temperature applications and general-purpose experiment input and output. It is built around an IEEE Eurocard subrack capable of housing up to 16 interchangeable daughter cards, allowing a fully populated system to support as many as 256 independent channels while drawing under 7.5\,W. This modular architecture allows experiments to expand on the existing daughter cards with ones tailored to their specific needs. There are currently three flavors of daughter cards: Resistive Temperature Device (RTD) readout, general purpose thermometer bias and readout, and load driver. The RTD board consists of a low noise lock-in amplifier that is limited only by device sensitivity over all temperature ranges. The general-purpose bias and readout board with chopping capability is primarily designed for thermometer diodes, but flexible enough to accommodate room temperature thermistors, Wheatstone bridges, optical encoders, and other devices. Finally, the load driver card can output an analog voltage for precise cryogenic heaters or it can be used to pulse width modulate high power loads. $τ$HK is a power efficient solution for experimental housekeeping needs that is suited for the the harsh environment of stratospheric ballooning.