The Tach-Rotor Adapter (TRA) works with 3-wire 12VDC fans commonly found in computers, computer power supplies, uninterruptable power supplies, DVRs, servers, and other electrical equipment with active cooling systems. The TRA converts a tachometer signal, also known as a speed-sensor signal, to a rotor-locked signal and provides fan speed (RPM) indication using an RGB (red-green-blue) LED.

TACH-ROTOR ADAPTER MANUAL 1.6.2

M. D. PENDLETON

[email protected]

M. D. PENDLETON

September 2012

INTRODUCTION DC fans are commonly found in computers, computer power supplies, uninterruptable power supplies, DVRs, servers, and other electrical equipment with active cooling systems. A noise reduction technique is to replace a noisy fan with a larger fan that spins slower, hence producing less noise, but without compromising air flow due to its larger size. Of course, there must be room to mount an adapter flange or manifold and the larger fan. Given the explosive growth of the computer industry over the last few decades, fans are available in a wide variety of sizes, speeds, and noise levels. Other features include built-in thermal detection with automatic speed adjustment, externally or manually adjustable speed controls, LEDs, etc. DC fans started out as simple 2-wire fans; one wire for DC voltage, the other for Ground. As computers evolved, 3-wire fans emerged; one wire for DC voltage (e.g. +12V), Ground, and a third wire called Sense. The signal on the Sense wire depends on the fan type; Tachometer fan or Rotor-Locked fan. Signal waveforms for Tach Fans and Rotor-Locked Fans are shown in Figures 1A and 1B respectively.

FIGURE-1A: TACH FAN WAVEFORM

FIGURE-1B: ROTOR-LOCKED WAVEFORM

Tachometer fans produce pulses on the Sense wire at a rate proportional to the fan speed. Fans with tachometer sensors are commonly used in computers as it’s a simple matter for the computer’s processor to compute and monitor fan speed. Rotor-Locked fans produce a static signal on the Sense wire that is in one of two states, FAIL (Locked Rotor) or GOOD (Spinning Rotor). For unattended equipment, Rotor-Locked fans are popular as they integrate easily into TRA Manual 1.6.2

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alarm systems due to their simpler 2-state outputs. The Tach-Rotor Adapter (TRA) has two main functions; Tach-to-Rotor Conversion and Speed Sensing and Display. Tach-to-Rotor Conversion: Rotor-Locked fans are generally not as common as Tachometer fans and are even harder to find in sizes over 92mm. With the TRA, a common computer fan (i.e. a tachometer fan) of any size can be converted for use in a rotor-locked application by simply inserting the TRA between the fan and the end-use equipment. Speed Sensing and Display: In the same way a computer calculates fan speed; the microcontroller in the TRA calculates fan speed and lights an RGB (red-green-blue) LED to a color indicating which one of four speed ranges, or bands, the fan is operating. The colors and bands, i.e. RPM ranges, are shown in Figure 2.

FIGURE-2: LED RPM COLOR BANDS

TRA Manual 1.6.2

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The full list of TRA features is shown in Table-1.

FEATURE

DESCRIPTION

Output Signal Select

Output sense-wire can be set to Tach Output (match fan input signal) or converted to Rotor-Locked Output

LED ON/OFF

ON or OFF

SELECTION METHOD DIP SW1 ON = TACH OFF = ROTOR-LOCKED DIP SW2 ON = LED OFF OFF = LED ON JUMPER ON = HIGH OFF = MEDIUM

LED Brightness

High or Medium

Flicker Suppression

Using a combination of filtering and hysteresis, Flicker Suppression prevents LED flicker caused by frequency noise, a slowly varying fan, or when the fan slowly crosses a band threshold

RESET

Resets TRA circuit

Fan FAIL

LED turns RED if fan RPM falls below FAIL threshold within 0.5 seconds. Fan Failure overrides LED ON/OFF setting.

FIXED

Fan RPM LED

LED color is based on fan speed (RPM) and is independent of Output Signal selection.

FIXED

FIXED

Momentary Button

TABLE-1: TRA FEATURES

TRA Manual 1.6.2

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KIT OVERVIEW The TRA Kit comes with a custom PCB board with required components and a case. A DIP switch allows user configurability. The PCB layout uses only through-hole mounting, no surface mount technology, allowing for simple-level soldering skills and quick assembly. The PIC16F88 microcontroller sits inside a solder mounted DIP socket allowing the PIC to be easily removed and inserted for firmware updates or if permanent placement is desired the PIC can be soldered directly onto the PCB, eliminating the need for a socket and reducing part count. Required Tools or Supplies (assuming pre-programmed PIC):    

Soldering equipment (Iron, Solder, Flux) Wire cutting and stripping tool Drill, 1/8”, and 13/64” drill bits Small screwdriver (slotted or Philips to fit case screws)

CASE TOP

13/64 “ CASE CENTER

0.45” 1/8 “

1/8 “

> 0.72”

0.50” 1/8 “

> 0.72” NOTE: DRAWING NOT TO SCALE

OPTIONAL FIGURE-3: DRILL HOLES

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KIT ASSEMBLY STEPS 1. Prepare Case and Fan Cables a. Cut the fan extension cable into 2 equal halves b. Drill holes in case as shown in Drill Holes Figure i. RESET hole is optional ii. Size the RESET hole for intended RESET device (e.g. 1/8” for toothpick, 13/64” for small screwdriver, etc.) 2. Install Components a. Solder 10 resistors b. Solder 1 18-pin IC carrier c. Solder 1 DIP Switch and 1 Tactile Momentary Switch d. Solder 2 capacitors e. Solder 2 transistors and 1 5V regulator f. Solder 1 2-pin header g. Solder 1 RGB LED to the PCB (note: mount RGB LED high enough so the LED pokes through the 13/64” hole on the top of the case) h. Insert PIC into the 18-pin IC Carrier i. If desired, put a Jumper on the 2-pin header j. Set DIP switch to desired settings 3. Install cables a. Feed cables through 1/8” holes in top cover i. Cable with MALE connector goes through LEFT hole ii. Cable with FEMALE connector goes through RIGHT hole b. Strip ~ 1/2” insulation from the 3 wires on each cable c. Solder cable with MALE connector to FAN-IN (see label on PCB) d. Solder cable with FEMALE connector to FAN-OUT (see label on PCB) 4. Assemble a. Gently pull/push on the wires to bring the PCB up against the case top b. Gently align the RGB LED to poke through the case top 1/4” hole c. Fasten the case halves together with the case screws

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JUMPER

DIP SWITCH -SW2 -SW1

RESET

FIGURE-4: TRA PCB LAYOUT TRA Manual 1.6.2

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FIGURE-5: TRA SCHEMATIC TRA Manual 1.6.2

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