The Lamptron FC5 (version 2, I think), is a four channel manual fan controller and temperature sensor bay device. The colour of the device backlight can be customised by fitting jumpers to one or more of the three (R, G and B) pins on the rear of the unit. MSRP of these units (at the time of writing) is around $60 (USD).
I was recently doing some repairs to my existing case lighting setup, and thought I’d try and control the backlight colour of this unit from my existing 5v microcontroller. It turns out that it actually surprisingly easy to do this. All you need to do is fit a MOSFET across the jumper pins and control the on time of the MOSFET using a PWM signal.
To fit the MOSFET to the FC5, you first need to find which side of the jumper is 5v, and which is the signal input. For my unit, the 5v was towards the bottom of the unit, while the top row of pins were the inputs for each colour.
For each colour channel (R, G and B jumpers), connect the source pin of the MOSFET to the 5v pin, and the drain pin of the MOSFET to the other. The gate pin is then connected back to a PWM output on your microcontroller of choice. In my case, my microcontroller is powered from the USB, so an additional wire for ground is not required. If your microcontroller does not share a ground connection with the PC, you will need to create a connection for that too.
And there you have it, simple control of the backlight of your Lamptron FC5 (v2). You will need to write supporting code to drive the PWM lines on the connected microcontroller. I do not know if this simple circuit will work for the version 3 FC5 (identifiable by the presence of voltage readings on the unit’s LCD) as I have not tested this.