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This project is a configurable low-cost solution to produce fake cooling fan TACH signals for various computer systems. It consists of three main parts:
With the code uploaded to Arduino, a complete Attach-Hexa is able to drive six computer fan headers (channels) with TACH signals. Users can easily adjust the required RPM simulation on each channel, using pre-defined commands on serial interface.
If you have a conventional computer system with ordinary cooling, you don't. However, Attach-Hexa can be useful in the following cases:
TACH signals are used to report the current RPM of cooling fans to the system. Each fan has a dedicated pin for this purpose, usually in the following pinout:
On most motherboard headers, TACH pin is pulled high (+10-12V) by an internal pullup resistor. As the connected fan rotates, it's own built-in electronics (hall-effect sensor, transistor) pulls the TACH line to GND twice in every revolution. This results in a square-wave with a certain period, which is proportional to the fan's rotation speed. So if we would like to reproduce this, we have to pull that pin low at a specified rate. Arduino and similar microcontrollers can do that easily from code. The following schematic represents square-wave generation on channel 1:
The custom pcb board is holding the Arduino Nano, and makes it capable of pulling +12V (or more) lines safely through transistors. The entire unit can be powered from any fan header (using GND & VIN pins) up to +12V, or from USB. The power source is automatically selected to the highest voltage.
The PCB's size is 91mm * 26mm measured by PCBWAY's system. According to KiCAD it is 91,338mm * 25,87mm.
The following components are needed to assemble the custom pcb.
| Component | Type | Package | Value | Quantity |
|---|---|---|---|---|
| R1-R6 | Resistor | SMD-2010 | 4.7kΩ | 6 |
| Q1-Q6 | Transistor | TO-92 | 2N3904 | 6 |
| Pin header | Connector | 2.54mm single row | 8-pin male | 1 |
| Pin header | Connector | 2.54mm single row | 15-pin male | 2 |
| Pin socket | Connector | 2.54mm single row | 15-pin female | 2 |
Note: 2N3904 can handle collector current up to 10mA with base resistor 4.7kΩ by forced saturation (current flows from TACH pin to GND through transistor C-E). It is possible to substitute transistors with another type, but keep in mind you have to recalculate base resistor values in this case.
You can manage Attach-Hexa over serial. Connect USB cable to Arduino, and use any terminal program with the following settings:
Available commands:
/channel 2 4000/led link 2/led multi 60/print/save| Command element | Min | Max |
|---|---|---|
| Channel number | 1 | 6 |
| Channel RPM | 1 | 32767 |
| LED link | 1 | 6 |
| LED multiplication | 1 | 255 |
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