Tach Rotor Adapter Kit

Fan Speed Indicator

Difficulty: Intermediate
Designer: M. D. Pendleton

The Tach-Rotor Adapter (TRA) kit 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-to-Rotor Conversion: The TRA converts the tachometer signal from a Tach Fan to a rotor-locked signal thus converting a Tachometer fan into a Rotor-Locked fan. With the TRA, a common computer fan 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 is able to calculate fan speed, the microcontroller in the TRA calculates fan speed and turns on an RGB LED to an pre-programmed color indicating which one of four speed ranges, or bands, the fan is operating.

Build your own tach rotor adapter

Required Tools and Components:

Description Mfr. P/N
Standard Regulator 5 Volt 0.14A 3-Pin TO-92 Box 78L05
MCU 8-Bit PIC16 RISC 7kB Flash 5 Volt 18-Pin Plastic Dip Tube PIC16F88-I/P
Socket, Shorting Black 2mm, Black, Close 7600A-R
Connector Unshrouded Header 40 Position 2.54mm Solder Straight Thru-Hole 7000-1X40SG-R
Socket, IC, 18-Pin, Dual Wipe, Soldertail, Low Profile, 0.30" width 6000-18DW-R
Switch DIP On-Off Single Pole, Single Throw 2 Slide PC Pins 2.54mm Thru-Hole 206-2-VP-R
Capacitor, Radial, Miniature, 7mm, 100µF 16V 100UF/16V 6X7-R
Transistor General Purpose BJT NPN 40 Volt 0.6A 3-Pin TO-92 Ammo 2N4401TA
Switch, Pushbutton, Tactile, Single Post Single Throw, Off-(On) EVQ11L07K
LED, RGB, Water Clear, T1-3/4, 2.0 Common Anode MCDL-5013RGBC-TL-A
Case, Plastic, 3.2" x 1.6" x 0.8" Black Abs plastic Lip Top 1551KBK
Resistor, Carbon Film, 1kΩ, 1/4 Watt, 5% CF1/4W102JRC
Resistor, Carbon Film, 4.7kΩ, 1/4 Watt, 5% CF1/4W472JRC
Resistor, Carbon Film, 330Ω, 1/4 Watt, 5% CF1/4W331JRC
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)

Drill Holes

Step-by-Step Instructions

Step 1 - Preparing Case and Fan Cables

Cut the fan extension cable into 2 equal halves
Drill holes in case as shown in Drill Holes Figure
RESET hole is optional
Size the RESET hole for intended RESET device (e.g. 1/8" for toothpick, 13/64" for small screwdriver, etc.)

Step 2 - Installing Components

Solder ten resistors
Solder one 18-pin IC carrier
Solder one DIP Switch and 1 Tactile Momentary Switch
Solder two capacitors
Solder two transistors and 1 5V regulator
Solder one 2-pin header
Solder one RGB LED to the PCB (mount RGB LED high enough so the LED pokes through the 13/64" hole on top of the case)
Insert PIC into the 18-pin IC Carrier
If desired, put a Jumper on the 2-pin header
Set DIP switch to desired settings

Step 3 - Installing cables

Feed cables through 1/8" holes in top cover
Cable with MALE connector goes through LEFT hole
Cable with FEMALE connector goes through RIGHT hole
Strip ~ 1/2" insulation from the 3 wires on each cable
Solder cable with MALE connector to FAN-IN (see label on PCB)
Solder cable with FEMALE connector to FAN-OUT (see label on PCB)

Step 4 - Putting it all together

Gently pull/push on the wires to bring the PCB up against the case top
Gently align the RGB LED to poke through the case top 1/4" hole
Fasten the case halves together with the case screws

About The Designer

Mark Pendleton Mark Pendleton has been curious about how things work since his childhood. Taking things apart has always been a hobby, however putting them back together proved more of a challenge which only further stoked his curiosity. Mark recalls his dad working on things with tubes and wondered what kind of light bulbs those really were and what made them tick.

Like his father and brothers, Mark earned a degree in Electrical Engineering and spent more than 30 years in high tech industries. Electronics became a major hobby in Mark's life after his wife inquired about an alarm clock that could also dim lights but small enough she could take it with her on travel. After 2-years and several prototypes, several devices remain in service in the Pendleton household after more than 12 years in operation.

Other hobbies include building and repairing computers, building and repairing video surveillance systems, and still taking things apart to see what makes them tick.