7 years ago. This is usually done on a special PWM capable pin on the arduino. Standard was developed with idea of backward compatibility with 3-wire fans. Arduino can do PWM at 5v which isn't enough for the 12v fan. Thick of it like a switch, when it's on, the fan receives power and spins, when it's off, it starts to slow down, a modulated series of pulses turn on and off the fan to reach the desired speed. The internal diagram of a typical three-wire fan is as follows: It seems that for once more, the manufacturers did not have the same wire provider, or their wire providers did not have the same colored-plastic provider... Two fans with 3-wire connectors may not have the same wire colors. Couldn't I use Arduino to detect that HIGH and somehow find out the frequency? Update October 13 2008 Vice-versa it is possible to use old 3-wire fan on new board with 4-wire header, but with limited possibility of PWM control depending on board logic. All fans actually can be controlled with PWM, but this particular type can also provide tacho feedback simultaneously, something that the 3-wire fan cannot do -under normal circumstances. In one end of the connector the fan is connected in parallel with the 12V (YELLOW - BLACK). Do I need to use two resistors in voltage divider fashion? Still i did not find any way of easy disassembling. The circuit in the fan detects when the magnet in the motor passes a sensor, and each time it pulls the sense wire to 0V. I haven't used an arduino before, but the atmega microcontroller in it has counter/timers which will allow you to easily count 10 pulses on one counter, and use a timer to measure how long it takes (or count how many pulses in 0.1s).Whatever language you are programming in should have a multiply/divide function available, so calculating RPM should be simple. Therefore, the fan is powered normally and the cable of the PSU can be used to power another device. (Too high a voltage or current, and you'll let the magic blue smoke escape). 2. The controller and the Hall sensor are always powered with constant current. I probably should have explained.. PWM == Pulse Width Modulation.. Just be sure to connect the pull-up resistor to the arduinos 5V supply, and not to the 24V for the fan. The 3-wire fan powers the Hall sensor and the controller from the same line that the coils are powered. The third wire is to detect the speed of the fan. Connecting a Timed Fan Unit | How to Wire a Bathroom Extractor ��� In this post, we have told that 4 wires come out in the Cooler motor, the Common wire is Blue.The Black wire is of High speed.The Red Wire is Medium Speed.And finally, Yellow wire Slow Speed which has the lowest speed. If you connect a ~10K resistor between this wire and 5V, the wire will be at 5V when the magnet is ��� During the disassembling, i broke some parts of the housing and a fin. RECOMMENDED WIRE SIZES: 8-10 GA: FAN POWER AND GROUND. Refer to Figure 2. You can also use White wire instead of Yellow wire, which is the same color code in most Coolers.. YOU CAN WATCH HERE THE FULL DETAIL WITH DIAGRAM TO WIRE A COOLER ��� There are several reasons that a brushless motor should be used, among them is the reliability, the power efficiency and the rpm feedback. Thanks a lot Mysteron347. But i have not find anywhere a norm that declares if the fan MUST operate or not with the 4th wire unconnected. There could be a manufacturer though that maybe felt like making something different, and either he removed this resistor or replaced the FET with different channel than normal. The base of the transistor is actually the fourth wire. Usually, for more flexibility, they have a male-female 4-wire molex power connector. The tacho signal from the No matter what color the cable has, it will be plugged in the same motherboard connector! It's important to note, that if you are using PWM, you'll need to use a stable PWM frequency, and time the reading of the sensor pin during the PWM on cycle, as the Hall effect sensor gets it's power from the same source as the fan coils. Assortment of 3 way fan switch wiring diagram. It has the permanent magnets fixed on the rotor, the stator carries the coils, there are no brushes, it has a controller... the sun is shining... it is of course a brushless motor. The three wires on a typical CPU fan isRed - Vcc (+)Black - Vdd (-)Yellow - Sensor (Hall Effect Sensor)You can control the fan using PWM. So this yellow wire, I'm assuming it's much like the control wire on a   servo? No matter how may fans i tested, and no matter how many sites i visited, i found no clue that this configuration will fail. Then how would I have Arduino save that data and how would I figure out it's RPM from that? The coils receive these pulses through the transistor, but the controller along with the Hall sensor are not affected at all. Yes, 2 or 3 wire fans can be controlled using basic PWM. There are actually 3 different types of PC fans. They carry the heavy load to keep your PC cool and functional, either by providing fresh air in the box, or by forcing the hot air to leave a hot surface by pushing cool air. 3. This output generates 2 pulses per one revolution of a fan. So if you just hook up the red and black wires to 12v, the fan works, but you no way of controlling the speed. The third wire, comes directly from the output of the Hall sensor. The motherboard will normally read the rpm feedback from the fan tacho. Teoretically is possible to use 4-wire fan like 3-wire on the board with 3-wire connector. The PWM signal from the motherboard sources 5V during the on state of the pulse, otherwise it's pulled to ground. 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