Introduction Fan control for the masses
Fan control. The Storm and Storm X controllers have been in users’ grubby little hands for a few months now, and one of the chief requests we’ve heard is that you want the ability to control not only the LEDs but also the fans that cool them. Well fear not, because we’ve listened and as of today we’re proud to announce that both the Storm and Storm X will ship with on-board support for fan speed control. The implementation on each of the boards is slightly different, and we’ll get into the technical nitty-gritty in just a few moments. Suffice it to say that you now have the capability to support speed control of widely-available PC fans.
PC fans generally come in three flavors as far as control is concerned: 2-Wire, 3-Wire, and 4-Wire. The 2-Wire version is dumb, and simply turns on when plugged in. The 3-Wire version is the same, except it will tell you the fan speed in rotations per minute (RPM). We’ll not concern ourselves with these two as they provide limited to no control over speed. The 4-Wire versions are what we’ll focus on because they accept a PWM signal on the 4th wire, and just like dimming your LEDs with PWM, they will adjust the fan speed via PWM.
Here’s where we get just slightly technical. According to the PC industry specification document, 4-Wire Fans are to accept a PWM signal at a frequency of 25 KHz. The reason why we can’t (or shouldn’t) directly tap off of the LED PWM signal is that that LED PWM signal is generally required to be in the 1 KHz range. Therefore we’ve had to do a little bit of tweaking to the underlying clock to achieve the specification’s 25 KHz signal. The new firmware imparts this capability to the Storm and Storm X, as well as integrating an easy menu system for you to select the fan speed.
For now, the fan speed selection is “set it and forget it.” You can specify the fan speed for when the LEDs are powered up, and the fan speed for nighttime mode. No more buzzing fans to interrupt the silence of night, plus extended service life for your fans. Some users have asked for temperature-feedback control of the fan speed. While we’ve considered this option as a gee-whiz addition, we felt it unfair to limit the fan control capability to those who opt to purchase a temperature sensor. Plus, the reality is that once you’ve set your LED schedule, the fan requirements shouldn’t vary much at all. Therefore once you’ve manually selected the speed necessary to maintain your desired LED temperature, you can sit back, crack a cold one, and enjoy the view.
Storm X: The Storm X has a slightly different implementation of fan control. It allows you to set the fan minimum and maximum PWM duty cycles (speed), and will output these settings on pin D9. The output will be the minimum value at Night, and the maximum value from Sunrise-Day-Sunset. Pin D10 operates as a digital output, providing at 0V signal at Night/Sunrise/Sunset, and a 5V signal during the Day. This can be used to run devices (via a relay) that only need to be on during the Day.
Storm: You’ll see a menu that reads “CH4 CH5 Fan? [Y/N]” which allows you to toggle between controlling fans or not. It is important to note that this setting specifically affects CH4 and CH5 on the controller and those are the pins that you should use to control your fans if enabled. Once [Y] is selected, the CH4 and CH5 channels will output 25 KHz PWM signals in accordance with the settings set in the “Set PWM Day/Night” dialogue. Therefore the signal will ramp between the two values, and you’ll want to pay attention that the fan ramps up with your lights so that nothing overheats during sunrise/sunset.
Different 4-Wire PC Fans can respond to an input PWM signal in different ways. Some fans never fully shut off, even when given a 0 signal – this is meant as a safety feature. Some fans will allow control down to zero RPM. All fans will have a stall speed, typically around 20%, below which they will attempt to – and fail – to spin. As a best practice you should have your minimum fan setting either above the stall speed, or at zero.