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Smart Fan HAT cools the Pi and passes the GPIO

Jan 8, 2021 — by Eric Brown 6,437 views

Sequent’s $20 “Smart Fan HAT” for the Raspberry Pi passes along the 40-pin GPIO for other HATs and offers an MCU controlled step-up supply for precise control. There is also an optional DIN-rail kit.

The Raspberry Pi 4 and other high-end Arm SBCs are increasingly requiring an accessory that was traditionally needed only on x86 devices: the dreaded fan. The fan increases the size, weight, price, power draw, and noise of your Pi while introducing a moving part that is vulnerable to failure.

But whaddya gonna do? On this increasingly steamy planet, many demanding RPi applications will otherwise suffer from performance throttle downs or even system failures.

Smart Fan HAT alone (left) and with Raspberry Pi
(click images to enlarge)

Sequent Microsystems, which has launched a variety of stackable HATs, such as a Mega-RTD temperature sensor HAT sthat lets you detect exactly how hot the world is growing, has offered up its own, stackable Raspberry Pi Smart Fan HAT. Sequent claims that unlike most of the Raspberry Pi fans and fan-equipped cases that have rolled out over the last few years, the Smart Fan rules because it passes through the full 40-pin GPIO header, enabling users to add more HATs.


The Smart Fan is “smart” in that it offers an MCU-controlled step-up power supply for granular controls. The HAT can also be stacked to cool other heat producing HATs.

The Smart Fan HAT is available for $20 on Kickstarter, where it has already won funding, with shipments due in March. There is also a $30 kit that adds a DIN-rail housing designed to house both the Raspberry Pi and the fan.

Two Smart Fans HATs stacked with Pi and additional HAT (left) and Din-rail kit with Pi and Smart Fan
(click images to enlarge)

The Smart Fan integrates an STM32 MCU that communicates with the Pi via I2C to control the HAT’s step-up power supply via PWM. The step-up converts the Pi’s 5V output to the 12V to power the fan “just enough to maintain a constant temperature of the Raspberry Pi processor,” says Sequent. The “whisper quiet” fan draws less than 100 milliamps from the 5V supply.

Smart fan step down diagram
(click image to enlarge)

You can download a Python script as well as a “command system” from GitHub that enables fan control from any program with a command line interface. A NodeRED interface enables browser control of the processor temperature. The Smart Fan implements a PID loop and adjusts the fan’s speed to maintain the specified temperature.

Further information

The Smart Fan HAT is available on Kickstarter through Feb. 4 for $20, or $30 with a DIN-rail kit. Shipments are due in March, and there are volume discounts. More information may be found on Sequent Microsystems’ Kickstarter page.

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