Qwiic Fan Control Module

AMC6821 based Fan Control Module with Qwiic connectors for integration into 3.3V MCU projects.

GitHub repository at Tecsmith/arduino-fan-control

Features / Specifications

This project contains 2 PCB boards:

• AMC6821 Breakout Board, allowing intergration via I²C to:
  • ESP-01 dev board,
  • Pro-Micro screw terminal board,
  • Wemos D1 Mini screw terminal board, and
  • Many other MCU boards from your favorite suppliers, like:
    • SparkFun Qwiic [Niwot, Colorado, USA]
    • AdaFruit STEMMA QT [NYC, New York, USA]
    • Smart Prototyping [Hong Kong & Shenzhen, China]
    • Core Electronics PiicoDev [Hunter Valley, Australia]
• Fan Host Board, supporting:
  • The above AMC6821 Breakout Board, and
  • the Adafruit EMC2101 Breakout Board

AMC6821 Breakout Board

• Host for Texas Instruments AMC6821 Intelligent Temperature Monitor and PWM Fan Controller
• Integrates into other 3.3V based MCUs (via Qwiic / STEMMA QT connectors)
• I²C breakout pins (SCL, SDA, 3V3, GND)
  • on board 2.2KΩ pullups, disable by cutting jumpers
• AMC6821 breakout pins (PWM, TACH, FAN-FAULT and SMBALERT. OVR and THERM are also available.)
• Power LED (green)
• 2x Qwiic connector (works with SparkFun’s Qwiic Connect System, or Adafruit’s STEMMA QT)
• Supports 2x PWM Modes (via Jumper)
• Supports 9x I²C Addresses (via Jumper)
• Includes an on board Temperature sensor
  • can be cut out for remote installation (use rotary cutter along break line)

Fan Host Board

• Powered from 12V + 5V power supply
  • or just 12V with optional 12V-to-5V (“7805” IC or Pololu 5V Step-Down) regulator
  • or just 5V for 5V fans
• Supports most industry FAN types
  • Molex 4-wire KK-254-47053-1000 connector
    • 12V PWM, 4-wire, with Tachometer & PWM control
    • 12V, 3-wire, with Tachometer
    • 12V, 3-wire, with Rotor-Lock
    • 12V, 2-wire
  • JST 2-wire connector
    • 5V, 2-wire

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On board jumpers

AMC6821 Breakout Board

JP0 & JP1 - {A0 & A1} - I²C Address Selector

A0 / JP0	A1 / JP1	7-bit	Hex	Address
GND	GND	0011000	0x18	24 ☆
3V3	GND	0011001	0x19	25
N/C~	GND	0011010	0x1A	26
GND	3V3	1001100	0x4C	76
3V3	3V3	1001101	0x4D	77
N/C~	3V3	1001110	0x4E	78
GND	N/C~	0101100	0x2C	44
3V3	N/C~	0101001	0x2D	45
N/C~	N/C~	0101110	0x2E	46

_{☆ = default setting
~ = Not connected}

JP2 - {PWM/M} - PWM Mode (for Frequency selection)

JP2	PWM Mode
GND	High Frequency range, 1kHz to 40kHz ☆ (25kHz)
3V3	Low Frequency range, 10Hz to 94Hz

• Actual PWM Frequency depends on Fan Characteristics Register, bits 3-5

JP3 - {I2C P/U} - I²C Pullups Enable

JP3	I2C Pullups
Both connected	2.2KΩ pull-ups ☆
Both cut	No pull-ups

• I²C Bus should have at least one set of pullups.

LED (JP4) - Power LED

LED (JP4)	LED function
Tied	LED active to show power state ☆
Cut	Power LED disabled

Fan Host Board

The AMC6821 fan controllers has a voltage range on the TACH and PWM pins of -0.3Vdc to 6.5Vdc.

⚠ Do not connect 12Vdc lines to the IC pins.

TACH Control cluster

For the AMC6821 (and also the EMC2101) the TACH (tachometer) reading is done on the TACH or SENSE pin of the fan. Most fans operate by grounding this pin once or twice per revolution - thus requiring a pull-up resistor.

12V Fans

For 12V Fans a voltage divider array of resistors (made up of R2, R3 & R4) ensure that the TACH pin on the IC is near the 3V range, and the SENS pin on the fan is in the 7V range.

TACH circuit with J1 (to 12V), J3 & J4 providing a voltage divider

5V Fans

For 5V Fans only a pull-up resistor is required (R2).

• JP2 must be soldered together,
• JP1 must have the 12V trace cut, and the 5V side soldered to center, and
• JP3 & JP4 must both be cut

TACH Control Cluster

In summary:

Jumper	for 12V Fans	for 5V fans
JP1	bound to 12V ☆	bound to 5V
JP2	cut ☆	bound
JP3	bound ☆	cut
JP4	bound ☆	cut

PWM Control cluster

Fan speed control is managed by the PWM signal from the AMC6821 (and also the EMC2101). This pin should always be pulled up to the reference voltage of the IC (not the fan!).

ℹ   The board does not provide a 3.3Vdc line. This is sourced from the daughter board GND pin.

An N-Channel MOSFET provides PWM fan speed control for 3-, or 2- pin fans

For 4-pin Fans

4-pin fans have a the fourth pin providing PWM signal to the fan internals. This is pin is enabled by default via the bound trace on JP6.

For 2-, and 3-pin Fans

2-, and 3-pin fans do not regulate speed internally, so a N-Channel MOSFET is used to provide low-frequency PWM control to the Ground side of the fan (avoiding the problems experienced in linear control at lower voltages).

To activate the MOSFET driver JP7 must be bound (and JP6 cut to prevent PWM to fan signal).

PWM Control cluster

In summary:

Jumper	for 4-pin Fans	for 5V fans
JP5	bound “to GND” ☆	bound “to MFET”
JP6	bound ☆	cut
JP7	cut ☆	bound

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Manufacturing

I have not sent these for production yet. Want to make sure the thing works on a proto-board first. I’ll update this page when done.

AMC6821 Breakout Board

• Schematic print: amc6821-breakout-v3.0.pdf
• Schematic source (EAGLE CAD): amc6821-breakout-v3.0.sch
• PCB design (EAGLE CAD): amc6821-breakout-v3.0.brd

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Fan Host Board

• Schematic print: fan-host-board-v1.0
• Schematic source (EAGLE CAD): fan-host-board-v1.0.sch
• PCB design (EAGLE CAD): fan-host-board-v1.0.brd

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Source Code

Currently under development … refer to:

• PlatfromIO examples: Tecsmith/arduino-fan-control/PlatformIO
• AMC6821 Library: Tecsmith/Tecsmith_AMC6821

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