Another Interesting Item

I thought this might be something some folks might be interested in. I am posting this as I had received it. Please contact the author below if you want more details or have questions.

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Mac Mini as a note block for the blinds?

The Mac Mini is small lightweight and yet one of the most performant apple computers out there.
So, if you don’t need a display… Why not use the mini as a notebook replacement?
You have heard of desktop replacements but yes you have quite correctly understood a notebook replacement is the quest we are concerned with in this article.

How the idea came about

I have been a blind computer user since 1995. First I used Dos than Windows and soon after that missing the accessibility of console based systems started to use Linux as well.
My discomfort always had been that Windows was giving me all the fancy apps I needed for daily work but lacked a proper terminal environment.
When I happened to hear about voiceover I was curious at once. A Unix based system with a terminal and builtin support for the graphical user interface?

In 2008 I renounced my windows machine for a macbook. Not after long however I found that I needed windows apps and the web experience in Safari was not quite what I expected.
I used a triple boot setup running Mac Windows and Linux along side with each other. This setup however required me to boot and reboot all the time. Moreover it was quite hard to setup and to keep in a consistent state. You know how often Windows tends to fail. Reinstalling an OS into a triple boot setup most likely involves ruining the other two. 🙂
Since I wanted to stick to the Mac just to watch the development of the voiceover technology I sticked to Apple Notebooks.
However I was constantly short of battery time while on the go. Windows never ran quite as cool as Mac os X does thus consuming my battery very quickly.

I finally stumbled upon the solution to most of my problems…
Virtualization.
Only to encounter a new problem.
Performance
Running Windows 7 on a Mac Os X host using Jaws for Windows rendered the investigation of large web sites as slow and sluggish as Safari had been in my experience.
What to do?
Get a quad core machine!
The new problem had nothing to do with computer science. It rather was about economics. Have you seen Apple’s price tags on modern quad core notebooks let alone the ridiculous prices for more memory?
And what’s more… Why should I be prepared to pay for a retina display and dedicated graphics? And so I was looking into a Mac Mini.
The ram was easily upgradable and it offered a quad core i7 for under $900.
I didn’t need a display and found the freedom of choice if I happened to need one for a particular situation quite compelling.
The mini has more usb ports than any Apple Notebook more connections for peripherals and still is nearly as easily carried around as a Macbook Air 13 inch.
A new problem however is as obvious as the rising sun at a new days dawn.
The Mini has no builtin battery. Being a desktop machine why should it?
There are three ways of approaching this problem:
– either you don’t care about sitting on the train working on your noteblock
– or you take a battery with you and connect the mini to it
but the Mini wants wall socket power or to be more precise 100-230VAc. The numbers are less problematic than the letters “ac” signifying that the computer takes not the power supplied by batteries but by power sockets.
I am aware that there were Minis out there which had an external acdc power supply. Those would be very easy to power from batteries but if you are in the market for a quad core machine you are bound to use these Minis that have there power supply builtin.
The former Minis have been and are widely employed as car hifi computers. Material can be found via a quick google search. So
I had a Mini late 2012 and thus it had an internal power supply. and so I bought a dc to ac power inverter. They are used to power electronic devices normally used indoors via the power socket in a car or on a boat. However measuring the input current and the output current even feeling the heat my inverter dissipated I was well informed that I was not only running a computer from my battery but a heater alongside it.
At last I told my friend who is a electrical ingeneer that he had to do the job for me.
Which job he asked wondering what my rather crazy mind had come up this time with.

We had to choose the third option:
Ripp out the internal power supply and connect the Mini’s logic board directly to the battery thereby avoiding the need for inverting and boosting the batteries voltage to wall socket specs and then using the internal power supply to feed the logic board with the smooth dc current it demands to survive the struggle of daily computing tasks. 🙂

The implementation of the project

Replacing or removing the power supply of a Mini involves taking it apart nearly to it’s last screw.
Fortunately the guys at ifixit.com have thorough guides on doing this for each and every Apple computer.
The next problem was to determine the polarity and voltage of the current supplied.
We were so fortunate as to hook up the removed power supply to a power jack. The device has a 9 pin cable connected. Four of them are hot the other five are ground. There is no signal wire or any resistor that needs to be pulled to activate the power supply. As soon as the device is connected to a wall socket it supplies a steddy 11.85VDC.
The problem with batteries is that while they discharge they drop in voltage. A three cell li-ion battery for example ranges from 12.6V when fully charged to 9V when totally drained. Would the Mini run on 9V? We tested it. The Mini quitted service at around 10VDC. But would the logic boards dc to dc regulators stand anything above 12V? We didn’t want to test. Economics after all played a vital part in the quest that rendered my Mini a heap of parts and screws for some three weeks.
There was an other problem. Without the power supply the Mini’s logic board would be exposed to any electrostatic discharges that one carried around. connecting the Mini and incidentally touching the hot pole of the connector could easily render the sensitive and highly integrated chipsets to a heap of useless silicon waste.

The solution to the problem of varying voltage as well as to the problem of electrostatic discharge obviously is a dc regulator.
Mojo-audio sells them for audiophiles. But these are linear not switching power supplies. They offer the best stability of voltage at the cost of efficiency. While power consumption doesn’t play a vital role for an audiophile audio server it does so in using the Mini as a mobile computer.
While we went the switching power supply route I have to thank Ben from Mojo who encouraged me to risk the life of my Mini. Switching dcdc regulator boards are widely used in all sorts of applications. However if you don’t order loads of them you are not likely to find them for reasonable prices.
And herein my motivation for publishing this article is based. For the project at hand we modified a spare board manufactured by Mekrell but if there were more people out there wanting to use the Mini as a notebook replacement one could design a board and have them made by these companies that do small series of boards from eagle designs for tinkerers.

Adapting the dc-dc board to our needs involved replacing capacitors so that they could stand the higher voltage and also modifying the voltage divider for the reference voltage.
We ended up with a board that supplied 11.6VDC at more than 5 ampere. That seemed stable enough. We checked for ripples in voltage and found it rippling with an amplitude of 200 milivolts at a frequency of some 200KHz. This seemed to fit the regulators switching frequency and we decided to give it a go.
Putting the Mini together again left loads of room where the former power supply had been located. One could probably fit in a super capacitor or a small lithium polymer battery inside the Mini. This would allow for using it in a car even while the engine started or stopped thereby making for a huge voltage drop. It also made possible swapping batteries or leaving stationary for mobile operation. while the Mini ran.

What we have got

A mobile Apple quad core machine for under $1000 equipped with a Samsung SSD 830 Series and 16GB of memory. It can be powered from batteries or even an old notebook power brick. Any voltage from 40 to 10 volts is possible. Even powering the mini from solar cells should be possible provided that you are not doing heavy load tasks and you have some buffering for changing weather conditions in place. It’s running smoothly for months now. I even tested stability using Prime95 torture test.

Currently I am using a small Apple usb keyboard and a braille display. The external notebook battery I shot from Amazon sat me back a cheap 99$. It has some 140Wh and supplies power for the mini running for 14 hours on battery alone.
While this is too much and the battery is to big and heavy it proves that the Mini can indeed be used as a noteblock for the blinds quite successfully.

I am using OS X more and more and run Linux and Windows 7 64 bit alongside in VMWare Fusion quite happily and have never encountered any performance shortages since then.
One of the best things with this setup is that a blind person is able to restore the whole setup on their own. Reinstalling Mac OS X from the web is a matter of pressing command+option+r and activating voiceover with the usual command+F5 and then following the installation routine.
Reinstalling the Windows and Linux virtual instances is a matter of retrieving the files from my backup server or from my time machine disk.

The only problem left is monitoring the batteries capacity. Currently the Mini would just pass out when the battery is completely drained. We are working on a micro controler solution here.

So if you are interested in the project drop me a line and we may look into designing the necessary dc-dc converter board as well as the internal battery.
Best wishes
Jeronimo@leierweg.net

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