Daniel Spilker

November 17th, 2012

USB Status LEDs for Media Center PC

Several months ago I replaced my broken digital video recorder with a home theater PC running Windows Media Center. Overall I was quite satisfied with the outcome, but it had two shortcomings. One was that visitors sleeping in our living room were complaining about the bright HDD LED flashing at night when the PC was recording. The other one was that we were frequently asking us if the PC was running because we forgot to turn it off or because it was recording something. The first problem can be solved with a simple resistor. The second problem was not so easy to solve since the case which I bought for the PC has no fancy display but only two status LEDs on the front, one HDD LED and one power LED.

Searching for a solution on the internet, I found the LEDSdriver tool distributed by Slick Solutions. It hooks into Windows Media Center and controls up to three LEDs connected to a serial (COM) port. Sounds great. Since I don’t care for the HDD activity, I can use that LED to indicate the recording status. But I chose an (almost) legacy free motherboard for the HTPC, so the system has no serial port. Luckily I had a FTDI USB to serial converter cable lying around which I used to build a small circuit with one LED to test the LEDSdriver tool. It worked great, but the final solution should be integrated into the HTPC case and should leverage the HDD LED of the case. So I designed a circuit which uses a USB to serial converter IC and which can be plugged onto one of the motherboards internal USB connectors. For prototyping I bought SparkFun’s SSOP to DIP Adapter 28-Pin because the FTDI FT232R USB UART IC is not available in a handy DIP package.

The final design can drive up to three LEDs and I also added potentiometers to be able to dim the LEDs.

You can find the Eagle CAD design files and a part list on GitHub. I used the OSH Park PCB service to make the boards and bought all other components at Digi-Key.

Soldering an SSOP-28 IC is not so easy, but doable. I have been using the board for several weeks now and it didn’t fail once.