December 2007
I wanted to build an ultra-quiet PC to be used for playing DVD’s, MP3’s, downloaded films, watching (and pausing) live TV, and such like. It runs the Freevo home theatre platform on Linux, and features an IR remote control (with wake from standby functionality), an LCD display, TV-in and -out, and can barely be heard even in a completely silent room.
The first task was to identify what the components are which generate noise. These are;
- Fan in power supply
- Processor fan
- Hard drive
- Optical (DVD) drive
The first of these I tackled by constructing a passively-cooled PSU, that is to say a power supply without any fan at all. This I did by mounting the power transistors from an existing ATX power supply onto a very large aluminium heatsink, so large that it remains cool without air having to be blown over it. Since there are lethal voltages within a PC PSU, I then made a cage out of perforated steel to cover the whole thing. This is the large box at the rear of the machine which can be seen in the photos with the case off.
To solve the processor fan noise problem, I attempted to run the system using a passively-colled Slot 1 PIII processor. Unfortunately, the fastest available was still not up to the job, and so I went looking for the quietest fan I could find. The one I have used is an Acoustifan, which when run at 5V (rather than the usual 12V) is almost inaudible, even at night.
The hard drive is a 2.5″ laptop hard drive connected via an adapter cable, which is also extremely quiet. To prevent vibrations from this transferring to the chassis, it is held between two pieces of foam rubber. The fact that the chassis is made from 18mm MDF, which has quite a high density, means that the whole thing does not resonate as much as a folded steel case would.
The area in which I had the least success was with the DVD drive - I could not find very much objective information online about really quiet drives, and ended up buying a couple which had been recommended on forums via eBay. The one which I have is still not ideal, but quieter than many others which I have come across. Some drives can be set to spin at relatively low speeds via software, but this one does not seem to respond to such commands.
As mentioned, Linux is the operating system installed on this machine, or to be more specific Mandriva Linux 2007. The DirectFB system is used so that no windowing system is needed, thus reducing system resource requirements. This is important since the processor is a PIII 1000MHz, about the lower limit of what can be used for this type of system.
TV out is provided with a Matrox G400 graphics card, which although pretty old has quite good Linux support and produces a fairly good picture (much better than the photos would suggest; it’s pretty difficult to take reasonable shots of an analogue TV picture!).
For watching TV, I have a Hauppauge WinTV-PVR-150 analogue TV card, which is the most appropriate here in the Netherlands where the majority of homes receive analogue cable TV through a coaxial wall socket. At some point in the future, it may be that it will need to be upgraded to one or other digital system.
I was very keen that it would be possible to put the thing into and out of standby using a remote control, just as is possible with most set top boxes. It took quite a bit of fiddling to get the system to enter suspend mode properly (and more to the point, come out of it), and indeed it turned out to be easier using the older APM system in Linux rather than the more modern ACPI.
The remote control is the one which came with the PVR-150 card, with a simple detector circuit wired up to COM1 as required by LIRC.
To get the system out of standby using the remote control, it was necessary to construct a small circuit which would detect the IR code for “on”, and send an interrupt to the computer via the WOL (Wake-On-LAN) connector.
Finally, a small 20×4 character HD44780 LCD display allows control of the system without the TV being on, which is useful when for example playing MP3 tracks. This makes use of the LoS-panel circuit, which interfaces to COM2 and allows the backlight to be switched on and off in software, which is used to power it down when in suspend mode since power is still supplied to the LCD display.
For practical reasons (cooling), and also because I quite like the look of the G5 Mac, I had a perforated steel case made to cover the MDF chassis. This was not too expensive, and works really well. The front panel is made from 6mm MDF, and both it and the case are finished with spray paint: matt black for the case, and dark metallic indigo for the front panel.