This ESP32 controller puts four fans on Wi-Fi, so you can manage your server rack's cooling with a phone

CoolMaker Lab has created an open-source, ESP32-based board that independently controls up to four PWM computer fans via Wi-Fi or Bluetooth. It supports RPM monitoring, individual power switching, and automatic speed adjustments based on up to four external temperature sensors. The board runs ESPHome firmware for seamless integration with the popular Home Assistant automation platform, providing a web interface and HTTP API for direct control.

For DIY enthusiasts building server racks, NAS systems, or network cabinets, this offers a professional-grade solution for cooling management. It allows granular control over fan speeds and the ability to completely power down fans for silent operation when cooling isn't needed. The optional addition of millimeter-wave radar for presence detection opens up creative automation possibilities, making it a versatile and well-designed tool for custom hardware projects.