O2 Joggler: Improving the Joggler's Cooling
- Category: Computing
- Published: Sunday, 19 September 2010 22:16
- Written by Justblair
The O2 Joggler was designed as a low powered Linux based communication device. The original hardware is in fact made by Openpeak. The Joggler was always intended for use with it’s own bespoke Operating system. It is clear from looking at Openpeak’s design that they never intended that the Joggler would use the full capabilities of it’s Intel Atom Processor. How can you tell? Well frankly the hardware designed to cool the processor and other IC’s has pretty limited abilities.
For those that choose to run other operating systems on the Joggler, this can be frustrating. Start using anything like processor intensive tasks with the diminutive tablet and quickly you will push it beyond it’s thermal limits. I tried it out for myself using CPU burn and within a minute or two the processor maxed out. The processor then went into a lower performance mode to protect itself
Lets have a look at the Joggler’s cooling hardware and see what can be done to improve it.
Disassembling the Joggler
The Joggler has no obvious screws to unfasten on first examination. There are some though once you remove the Joggler’s information label on the back of the device. It was relatively easy to lift this label without damaging it, ideal if you wish to retain the information that it contains.
I used a craft knife to lift an edge and then simply peeled the label off gently. Once removed the label reveals 4 recessed screws that were easy to remove with a fine Philips head screw driver.
A plastic card, for example an old credit card or in my case my old blue Sky Card can be used to split the Joggler open. I would not use a screw driver for this task as the plastic that has been used to make the case is pretty soft and easy to gouge into. Somewhere I do have a really useful tool designed for this specific job, like all the best useful tools it chose to do a disappearing act. It looks like a thick plastic guitar plectrum with sharpened plastic corners. A credit card will do in an emergency though.
The Joggler is held together with plastic clips around the edges of the case, but once the plastic edge of the card had separated the two halves, it was just a matter of running it around the circumference of the device to open it.
The Joggler when opened splits into two halves, the motherboard, Wi-Fi module, speakers and power connectors all mount to the back half of the device, the touchscreen module to the Front. A JST style connector attaches the wiring for the touch screen to the motherboard. Some yellow cellophane tape needs to be gently lifted before prising the white connectors from the motherboard. With that is safely done the front assembly of the Joggler can be removed and placed somewhere safe.
The motherboard is held in place with five screws, as well as these an Earth strap must be unscrewed from the case before the motherboard can be lifted clear. It is also attached to the back section of the case with a module that contains the power connector and network cable input. To remove these I had to lift the Joggler motherboard out gently and fold it down onto the desk. A black plastic box also had to be unscrewed.
A plan was formed
You can see in the image above how the Joggler cooling is achieved by Openpeak. The heat-sink if it can be called that is made of plastic. It serves its duty more as a back plate which presses a rubber sheet against the hot chips on the Joggler’s motherboard. This rubbery membrane is a thermally conductive material. It transfers heat to the black plastic heat-sink/back-plate and more importantly to the heavy metal stand at the rear of the Joggler. This I suspect does more of the heat-sink duties for the Joggler than the plastic sink, despite its fins.
Thankfully the Atom processor does not produce copious quantities of heat, only around 2 watts max in fact. This heat transfer material does not have the lowest thermal resistance. Neither for that matter will the plastic sink. Obviously this design was never meant to dissipate larger amounts of heat. My guess is that the designers did not even envision the processor operating at full speed (and hence the full 2w heat dissipation) often if at all.
For this modification, My intention was never to produce a solution that could cool the processor operating at full speed for prolonged periods of time. My intention is that the Joggler behave most of the time as a Squeezebox style music client. This modification will ensure that it never hits problems on the rare occasions when it may be worked harder than this. I may use it occasionally as a test web server. If I had wished to give it more processor intensive duties I would perhaps be looking to add forced fan cooling, a quick and easy way to substantially increase the cooling to the chip.
My plan formed pretty quickly. I keep a box of heat-sinks which I have gathered over the years. I looked through for heat sinks that were approximately the correct size. I have seen a few projects that add additional cooling to the Joggler. The main way to do it it seemed was to glue heat sinks directly to the atom processor of the Joggler. PC Northbridge or passively cooled graphics card heat-sinks have been used by others and it is clear to see why. They are approximately the correct size to fit the case of the Joggler and easy to come by.
The problem that I saw with the other projects was that in order to get the heat-sinks to fit, one or both speakers had to be removed from the Joggler. The other thing I noticed that I thought was a shame was that the heavy stand would no longer be employed as a heat-sink. It seemed to me that in these projects the benefit of the stand was being lost. Of course add a cooling fan and the need for the stand as a heat-sink was negated.
Instead I decided I would aim to replace the plastic back-plate with a metal version. That way I could retain the overall design of the original cooling system but enhance it. I played around with a couple of sinks, but shaping them to match the plastic heat-sink was looking like a lot of work.
What I did discover was a scrap sheet of aluminium that was approximately the same width as the plastic heat-sink. I thought that instead of trying to cut down a larger heat-sink to match the size and contours of the plastic heat-sink, I would start with the aluminium back-plate and attach smaller heat-sinks to it. Although this would still be a fair bit of work, it looked far less formidable than reshaping a larger piece of metal. I would also retain the original rubber heat transferring membrane. This would mean I could work to less demanding tolerances.
First step then was simply to trace out the shape of the Joggler’s plastic heat-sink and cut out the basic shape. Using a mixture of hacksaw, drills and files this was a reasonably easy though time consuming thing to do. This involved a process of cut, offer up to the original and then fine tune the shape with the files. Aluminium makes this job easier as it is a pretty soft metal.
The plastic heat-sink though mostly flat does have some ridges and recessed sections. These were replicated as much as is possible via either carving out the metal with a Dremel or adding additional aluminium cut from thin sheet that I also happened to have some scraps of from another project.
This part of the project took probably the longest. I would describe my end result as somewhat roughly hewn, but that is relatively unimportant. One it would not be seen at all when the Joggler was reassembled and secondly the rubber heat transferring membrane will form to any small imperfections in the back-plate.
The heat-sinks I chose in the end were a gold coloured heat-sink that had originated from either a motherboard or graphics card originally. I also had some gold coloured memory coolers designed to cool individual memory chips on a Graphics card. There was not much science involved in my selection of heat-sinks, they were approximately the correct size for the available space and matched each other colour wise. There was a little fettling required of the larger heat-sink to make it fit the space.
Although the intention was to make the replacement heat-sink a close match of the original, I wanted improved cooling as well. For this I was going to extend the cooling a little out the back of the Joggler case. This meant a little modification of the Joggler’s rear section of case. I was able however to retain all the working features of the Joggler.
In other examples that I have seen, the modders removed at least one of the Joggler’s speakers in order for the heat-sinks to fit directly to the processor. By using the aluminium plate to move the heat sideways, I could place my heat-sinks pretty much anywhere the case let me. Never less, some of the internal plastic needed trimmed out, including the speaker housings.
The final job was to bond all of the parts of the new heat-sink assembly together. I used Arctic Silver thermal adhesive to glue the heat-sinks and aluminium spacers to the aluminium plate. Thermal adhesive is a two part resin with silver particles suspended within, it has reasonably good heat transfer powers and is ideal for this job. The trick I found with this part of the job was to assemble as much in the Joggler case as possible and then glue the heat-sinks in place within the Joggler case. This assured that all of the parts lined up with the holes I had cut in the case.
The Joggler was then reassembled with the rubber heat transfer membrane in place exactly as before. Heat is still transferred to the chromed metal leg of the Joggler though a quick feel of the new metal heat-sinks confirms that they are handling the majority of the thermal load of the system. They are warm to the touch.
The results at least visually speak for themselves, as long as you don’t inspect the Joggler too closely, the heat-sink modification looks pretty close to machine manufactured. If I had painted the heat-sinks black perhaps it would have looked even closer to stock but as the heat sinks reside on the rear of the Joggler I considered this overkill.
(above: Before and After shots of the Joggler’s rear)
The proof in the pudding I suppose should be performance. I did my best to measure the performance of the machine before and after the modification. Running CPU Burn in Linux I monitored the Atom processor. Under the original heat-sink arrangement, the processor very rapidly reached the point where its performance was being throttled due to reaching it’s maximum temperatures. With my new heat-sink arrangement, throttling did occur, but after ten minutes of the processor being stressed.
This I consider a success. Of course if had I wanted to create a cooling solution that would allow the Joggler’s processor to run at full speed under stress for prolonged periods of time, this passively cooled arrangement would not be good enough. Like others have found out, even a slow moving cooling fan is capable of cooling the Joggler more efficiently. However, I do not intend to use the Joggler for processor intensive tasks and I certainly do not want to add fan noise to a currently silent device. More important for me is that for short spells of time the processor can be stressed without the performance being strangled by overheating. For the use that I am putting the Joggler to this is an appropriate level of cooling and far better than “good enough”
Thinking about taking on such a project? Difficulty wise it is not that bad, though patience is required during the “cutting, test-fitting, filing some more” stage.