Extending the Joggler’s USB Capabilities
- Category: Computing
- Published: Sunday, 07 November 2010 01:38
- Written by Justblair
The O2 Joggler (A rebranded OpenPeak device) is out of the box a fairly mediocre device. However when it started selling at a £50 price mark quite a few hackers got interested in the capabilities of the Linux driven unit. Now there are a number of software options available to Joggler that take it from mid table obscurity to being a top performer.
I have already investigated improving the cooling on the Joggler and replaced the standard cooling system with something more substantial. I have also been using and improving the Squeezeplay software ported over by Tarkan.
All in all my Joggler is providing excellent value as a touchscreen media player on my headphone rig… But I had a niggle or two left to solve… Here is the problem, a standard Joggler has one side mounted USB port, and that is awkward and limiting in equal measure. Time for change!
First of all lets just look at how limiting this one USB port actually is.
There are two issues as I have already mentioned.:
I am using LittleDot DAC_1, a USB DAC (Digital to Analogue Converter). This device takes the digital musical output from the Joggler and converts it into very high quality Audio. Not to rubbish the Joggler too much, but it’s internal speakers are never going to light up your ears (think portable radio quality). But with the right software and the LittleDot DAC the Joggler is a low budget high quality music source. That is providing you have a USB cable hanging out the side of the Joggler. Elegant this aint!
Secondly, from time to time I want to make use of other versions of Linux on my Joggler, mostly for hacking (and the subsequent recovery of the Joggler’s original software). This means running Linux from a USB stick and preferably using a keyboard for some command line Kung Fu. Again you see the limitations straight away… Now we need an external USB hub, not very elegant!
Is such a shame as the Joggler is such a delightfully designed object that as soon as I get it to do something useful, I have to make compromises visually. Well time to change this.
I have already shown how to tear down a Joggler in my cooling article, so I will not repeat myself. So on to the USB stuff. My intention was to modify the Joggler’s USB capabilities in two directions, number one was to add an internal SD card reader which will be used to transfer media to the Joggler or to run alternate operating systems from. Number two on my list is to add a captive USB “Tail” to my Joggler. As my DAC will be plugged in permanently to the Joggler, a hard wired USB cable makes sense and will be a lot neater.
So lets start with the SD card. Opening the Joggler reveals that between the capacitive touchscreen and the motherboard of the Joggler is a limited gap. I had a portable USB card reader already that I thought could be pressed into service within this tight gap. Supplied free with an internet purchase of an SD card this is a pretty cheap device. The ideal width (almost) and the ideal price (free)… I had a donor!
The plastic casing unclipped very easily. It revealed the guts of the reader. Looking at it side on I could see that this was not light enough. The 3mm LED activity indicator protrudes from the assembly and the metal USB male plug will be surplus to requirements. Using a soldering iron, snips and a solder sucker these parts were removed and four cables soldered to the pads left vacant by the removal of the plug.
I used heavier cable stripped from CAT5 cable (My favourite source of ultra cheap hook-up wire) for the power and ground. For the Data+ and Data- connection I used finer mylar coated hook-up cable which is easier to solder to tiny through hole pins.
After a test fit, it was clear that I was going to need to space the SD reader off of the motherboard, both to make it easier to marry the card to the outside case and also to avoid shorting the motherboard with the connections to the metal cowl of the reader.
I then mounted the SD card to the board with more glue. There is a reasonable amount of space there, I adjusted its position so that the SD card would protrude slightly when inserted. I could have mounted it so the SD card was even neater by moving an earth strap but it was close enough for me and still allowed me to retrieve the card easily.
The data connections hopefully you can see in the image. The power (5V) is attached to the 5V line of the existing USB socket. Now this is not something you would ordinarily do lightly. The USB specification states that a USB device must be capable of providing 500ma or current to a connected USB device, that is also (no coincidence) the maximum current draw that a connected device is allowed to draw. So to piggy back the power supply of a USB could be dangerous as theoretically I could now have two 500ma devices (i.e. 1000ma) attached to a socket rated at 500ma.
That is of course if the manufacturer (in this case OpenPeak) has provided a USB socket that only is capable of providing the minimum current. I decided to investigate the USB power supply on the Joggler. The Joggler connects the 5v supply in its USB sockets (there is an internal socket as well) near directly to the incoming 5v of its power supply. For safety there are two fuses which I was able to identify as Bournes 0805 PTC Resettable Fuses part number MF-PSMF110. These the datasheet tells me have an Itrip (the current they trip at) of 2.2A. Theoretically then I could connect up to 4 USB sockets to the power line without fear of tripping the fuses. One more wont hurt then.
The data lines are connected to two points on the motherboard that were identified in an article on the now removed Joggler wiki. In the photo above the white cable is connected to the Data- and black to D+. The ground I found a point very close to the mounted reader.
To complete the modification I used a fine file to erode an SD card shaped hole in the outer case. If you don't look too closely this is a pretty neat job, and as it is on the side of the case, it is out of immediate sight most of the time.
Before I tightened up any screws however I had a second modification to make. The hard wired USB cable. Not only was this going to look neater, it would free up that side USB port in case I want to attach a keyboard to dabble with the Linux command line.
The first thing to do was to decide where the cable would enter the Joggler. I picked a spot on the case just behind the internal Wi-Fi USB device. I chose here because it would be reasonably easy to route the USB cable around the motherboard from here.
I drilled out a7.2 millimetre hole here, this is a little larger than the width of a USB cable. But I used a rubber grommet from Maplin Electronics (product code QT93B) both because it created a neat finish and also to prevent sharp edges on the case damaging the incoming cable.
On the inside I was getting a bit short of space so I had to shed the heavy protective skin of the USB cable pretty much the moment it enters the case. A liberal dose of hot glue whilst not pretty, secures the cable.
The green and white cables within the USB cable solder to the motherboard. Again the now missing Joggler wiki had the info I needed, but you can see on the photo where to solder to.
The 5V and the Ground lines this time attached to the internal USB sockets power and ground.
The Joggler can now be reassembled and once tested the screws fitted to secure the case. Both USB modifications worked first time, always a relief, even when the soldering work is pretty basic as in this case.
Here it is in all it’s glory, the only modification I have done on equipment where there is less to see than before.
Incidentally The Joggler is attached to a LittleDot DAC_1, acting as source for a LittleDot MkV Headphone amplifier. Headphones on the left are my closed design restored vintage Koss Pro4AA set, to the right are open Sennheiser HD650s. The Koss are fine for listening when my significant other is watching TV as the closed design does a good job of isolating noise. The HD650s provide the real quality listening but leak sound like crazy so are reserved for more private moments.