Tech corner

Supercapacitor + Raspberry Pi

I have been interested in supercapacitors for a while. These components are boosted up versions of the humble capacitors found in most electronic products. A capacitor is a component that can store energy, in a similar way to a battery. Normal capacitors – aka caps – only take very small charges (typically measured in Microfarads), and they are often used for cleaning up spikes and noise in power supplies. Supercaps can store much more (measured in Farads), which presently makes them almost suitable as battery replacements.


What’s wrong with using batteries?
– They take a long time, and fairly complex charging circuits, to charge. A super cap can be plugged in a standard power supply with addition of just two components, and charge in minutes.
– They have a limited life span, generally around 1000 charges, after what they have to be recycled, a tricky business. In theory, a well-treated super cap will last almost forever.

I have run a couple of tests with current supercapacitor technology. I found all the info I needed about supercapacitors in this instructable.

Super capacitor battery, 8V 120 Farad

One if my experiments was to build an 8.1V, 120 Farad capacitor array, that should be sufficient for powering a small robot or microcontroller. It is made of 6 x 360Farad, 2.7V supercaps. First test: to supply power to a Raspberry Pi. It works fine, but with this configuration (8V 120F converted to 5V) I only get approximately 15 minutes of operation, and that’s without powering a display.

The bright side is the speed of charge, around 3 minutes with my bench power supply (2.5A).

Erm… Not sure what these supercaps will be good for, maybe a secondary power for mobile robot. The fast recharge rate could make it a good combination with a conventional battery to provide continuous operation.

Dynamo mini audio amplifier

Finally finished the mini audio amp I started when I visited Flowering Elbow. I fitted a supercapacitor array inside the amp, that gives approximately 20 minutes of operation when fully charged. Charging it with one of my modified dynamo torches takes 3-4 minutes.

Finger dancing optional. Music is Chocolate by Syrup.

The Magpi, Raspberry Pi magazine

I am gradually getting to grips with the Raspberry Pi, and I have stumbled upon a great online/hardcopy resource called The Magpi.
Currently at issue #20, The Magpi started in 2012 to deliver a monthly selection of articles written by enthusiasts about various Raspberry projects, features, and culture. All the issues are available online, and are a perfect repository for beginners and intermediate Rpi eaters.
The feel, layout and content of the magazine bring back a community based DIY computing spirit very close to that of the 1980s, which I guess the Raspberry Pi initiative is very inspired by.


The Magpi is currently running a kickstarter campaign, already 341% funded with 13 days to go!

Crunchbang linux on macbook


Yet another attempt at moving away from the macwindroid world, as I am totally, in principle, pro open-source, gnu libre linux big corps get your greedy finger off my (raspberry) pie.

But, having tried a couple of times to run linux on the PCs in my studio (red hat linux in 2005, ubuntu in 2009) and finding myself booting back into windows after a couple of days/weeks, I eventually regained the hard drive space and removed the linux partitions.

Perhaps re-motivated after seeing Richard Stallman, founder of the Free Software Foundation, speak at Lincoln University in October, I started looking around once more for a linux distribution (distros, as they are called in linux world, are variations on the linux operating system). This time I decided to install it on my main computer, a 2009 macbook pro. I tried ubuntu which I found too bloated, trying too hard to be user friendly, which it is only to a certain extent. I tried kubuntu, puppy, and finally settled on crunchbang (aka #!), a debian variation with a nice-stripped down, no messing around feel, a sort of geeky elegance I liked (screenshot of crunchbang’s default desktop below).


Furthermore, I was at the same time taking my first steps with a raspberry pi running Raspbian, another Debian distribution which I found rather pleasant to use. All went rather well, I first installed rEFIt on my macbook, a small app allowing choice of operating system at startup. Then I installed crunchbang from a downloaded install DVD, a straightforward business.

Almost all is running fine, but I am still not using crunchbang much. The reason is that after spending hours tweaking the parameters on the crunchbang trackpad controller (synclient) I never managed to match the smooth, transparent control offered by the mac version. I feel distanciated and frustrated when I use the machine under crunchbang. The human-machine interface all of a sudden becomes clumsy, making the machine unfriendly. It is a pain to have to use a mouse on a computer fitted with such a good trackpad.


Not giving up yet, I installed Crunchbang on an older macbook, a white plastic one from 2006. This one has a rough clickpad to start with, and it responded very well to the installation. All is working, even the sleep function (which does not work on the macbook pro).

I am going to get two days of training with real pros, the guys at Access Space in Sheffield. They have been running Linux on recycled PCs for more than a decade, training and converting many users to the joys and pains of open source computing. I will take my crunchbanged laptop up to their lab and hopefully get the beam of dark light I still need to make a more committed step into gnu-linux. In return for the training I shall deliver a robotic workshop to Access Space users in the near future. Watch this (access) space…


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