Tuesday, 4 December 2012

MK802 Project - NAS Assembly

Using some parts I had lying around, namely an external USB SATA HDD caddy, the HDD from my existing NAS and a few USB cables, I was able to assemble the MK802 NAS - Phase One:

This all runs using the single DC adapter for the external HDD caddy.  I am powering the MK802 using the first USB port on the HDD.  The second port has a second WiFi adapter plugged in, to allow me to bridge the WiFi interface that will run in AP mode on the MK802, with the existing WiFi router.  This will allow me to set up the device with access to the local network and internet (required for updating / downloading packages).  All of this is hooked up to the second USB port on the MK802, via the USB input on the HDD caddy, thus allowing the HDD caddy to act as a four port hub too.

The HDD caddy was purchased a few years back on Amazon for around £15 including delivery.  It has served me well and makes for a good hot-pluggable HDD caddy.

I have Debian running on the MK802 with a sunxi 3.0.36 kernel.  I will provide details on how to set up the MK802 with Debian using an SD card.

Related: MK802 Project - Heat sinks

Saturday, 1 December 2012

MK802 Project - Adding heat sinks

I have just bought an MK802 Mini Android PC.  My intention is to use this powerful but small piece of kit to create a replacement for my dated NAS.  It will serve as a router, wireless AP, firewall, NAS, NIS and NFS server.  It is some 6 times more powerful than it's predecessor, with 10 times more memory.  It cost just over £30 including delivery and runs at 3 watts; some 8 watts less than the current NAS.  It also has USB 2.0, replacing the previously poor USB 1.1 from the predecessor.

Phase one will involve using my existing 3.5" HDD, running in an external USB caddy.  This will server as the NAS storage, while the OS is run directly from the 8GB UHS Micro SD card.  Using u-boot, it is possible to boot a custom linux kernel from the SD card and boot an entirely different OS.  I will be sticking with Debian ARM, since it has served me so well.  I will be restricted to the 3.0.36 kernel for a while, downgrading from 3.4, since the Allwinner A10 SOC drivers have not yet been ported to 3.4.  However, 3.4 is currently in WIP status, so I should be able to return to this version very soon.

Phase two will see the introduction of the 2.5" external USB HDD, powered by USB and thus losing the need to power the drive separately.  I'm not sure how the MK802 will cope with providing this power throughput, though you have to wonder how affordable a 500GB SSD will be by that point...

Before doing anything though, I have read a few reviews that suggest the MK802 gets hot when operational.  This is understandable given it's running a 1.6 GHz CPU and a dual core 500 MHz GPU and 2 x 512 MB DDR3 memory modules.  The solution is quite brutal, but simple: add heat sinks!  Since the whole design is based on it being minimalistic, some surgery is required.  If you care to follow it, I have prepared step by step instructions:

Step 1: Dismantling the MK802

 You will notice a thin layer of plastic attached to the thicker base layer.  This thin layer is just clipped in place and can be removed by carefully inserting a Stanley blade into the end with the HDMI connector, and carefully twisting until the two elements separate.

Before getting dirty and hacking a whole in your casing, you should try to work out an area that will provide the maximum coverage, while not shorting anything; remember, the heat sinks are metal, so have the potential to short something if carelessly placed.  Once you know where that will go, line up your four heat sinks
in single file on the inside of the lid part of the casing, precisely where they will protrude.  Now carefully mark an outline using your Stanley knife.  Don't press hard, you are only making a guide for when you will cut, so just a light scratch in the surface will suffice.

Step 3: Modification of the casing

With the template engraved in the lid, you can remove the heat sinks and begin cutting.  Be patient and gentle with this, since trying to press too hard and cut all the way through will result in cracking the plastic or slicing a finger.  Just gently score the surface, one edge at a time, repeating the same pattern until you notice the knife begin to make it's way through.  This part took me about 20 minutes to complete, but it's worth taking your time.  I have seen some people use electric hand tools and make a complete mess of the casing, so it pays to be patient here.

If you want to improve the finish even further, then you can also use a nail file to get rid of any burrs.

Step 4: Assembly and adhesion of the heat sinks

It is better to assemble the casing first, before adhering the heat sinks, since it will be easier to get them in the right place.  You can use the hole in the case as a guide for alignment.

After adhering all the heat sinks, you should have something that looks a little like this:

I have seen some other articles where holes are drilled in the surface to allow more ventilation.  This really isn't at all necessary, since the heat sinks are fairly efficient at radiating heat on their own, thus drawing cooler air through other cavities such as the USB ports, SD slot or HDMI slot.

Remember, when operating, keep the heat sinks on the top most surface, since they will not function correctly if they cannot radiate heat upwards.  It is okay if the heat sinks are on the side, providing the assembly is kept horizontal.  Vertical positioning will result in radiated heat preventing either the GPU or DDR memory from getting sufficient cooling.

To test that they are working adequately, turn on your device and wait a minute or two.  If working correctly, the heat sinks will be hot to the touch.