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At work I have an core i3 iMac 21.5″ from Mid-2010.

Unibody iMac computers are great machines but I cannot stand the glass panel: It looks great but it’s a nightmare to have a piece of highly reflective glass between your screen and yourself.
I don’t really understand why apple did not offer the option to have the computer’s glass panel replaced with a black mat plastic bezel. I’m not talking about the LCD screen, but just the glass panel that can easily be removed with suction pads to get inside the computer.

I asked my boss if he would mind if I removed the glass panel altogether and left the computer’s LCD screen and edges exposed. He reply he would mind adding he wouldn’t really like the look of it and also so that the computer would gather dust and that maybe water would eventually find it’s way inside the computer…

A couple of weeks later had a brainwave: I should be able to use diamond cutting discs and my dremel to cut out a window into the glass panel thus eliminating the annoying reflections.

I did so and… it was a bit a disaster.

It’s virtually impossible to cut a piece of glass with a dremel and cutting discs without breaking the glass. By the way, cutting glass with a rotating tool is dirty and dangerous business:

• Wear a breathing mask unless you want glass dust in your lungs.
• Wear protection glasses (I felt on several occasions small shards of glass hit my hands and face!).

The good news is behind the black bezel of the iMac’s glass panel is a thin metal frame that sticks to the glass and holds it together even when the glass is broken.

Once the window cut out of the panel I used a large sheet of black vinyl to cover the sharp edges of the panel and render it mat.

Check out the end result bellow. I am really thrilled with the results: No more headaches and annoying reflections between the LCD screen and my eyes!

There are still reflections from the glossy LCD screen but these are not a problem at all as the surface of the screen is treated just like macbook air screens’ are.

Batteries on the Magic Trackpad last an amazingly long time. I would say about 6 months for my usage (on alkaline cells).
Nevertheless, eventually running out of batteries is always annoying so the other day I decided to power the Magic Trackpad using an USB cable.

This mod has already been documented on macrumors.com’s forum. My twist on it was to drill a hole in the stainless steel battery compartment cover instead of leaving wires exposed or drilling through the trackpad’s body.

Be warned that drilling stainless steel requires a lot of patience. You also need a drill that can rotate a slow speed and Cobalt drill bits. It is really important to take your time and not to drill for too long otherwise the heat will turn the stainless steel into super hard steel you will not be able to drill through.
In the case of that battery cover, being small it will get hot very quickly so I drilled for 30 seconds at a time, waiting a minute or two in between to allow for the piece to cool down.
It took me a whole afternoon to drill through the cover!

I used three 1N4001 diodes in series to step the voltage down a bit (from 5V to about 4.2V). You could use an extra two to bring the voltage closer to 3V, but the trackpad doesn’t seem to mind being powered by tensions over 3V (don’t try with more that 5V though) (I’m pretty sure Apple’s engineers used regulators to protect the trackpad’s internals).

In the process, I discovered that the positive end of the battery ersatz have to reproduce the shape of the + side of an AA battery. If the + end is flat it will not work. There is clever mechanism that doesn’t close the electrical circuit to prevent from damaging the trackpad if you insert the AA batteries in the wrong orientation.

Ingredients:

• A small piece of soft wood, cut down to the dimension of two AA batteries in series
• Electrical tape
• A beer cap (for the negative pole)
• The positive tip of an AA battery
• A couple of 1N4001 diodes to step down the USB voltage

Bellow are a few pictures of my mod. Enjoy!

Band: Bitter Ruin
Song: A Brand New Me
Album: Hung, Drawn & Quartered

Download this tab.

View this tab on google docs.

Recently, I found a gorgeous looking bicycle rear light on eBay.

It was a bit rusty but after cleaning it the following markings on it became readable:

• Miller
• 597

Unfortunately, I couldn’t find much about on Miller as a bicycle light manufacturer and the different models they used to make… If anyone knows about it feel free to leave a reply at the bottom of this post.

597 rear lights are bottle dynamo lights so there is only one piece of wire coming out of the back them, but I converted this one to work of my hub dynamo!

With a  bottle dynamo fitted on your bike, the frame is the return path of the electrical circuit and you only need one piece of wire that runs form the dynamo to the lights to bring the current to the light bulbs.
With dynamo hubs, the frame is not part of the electrical circuit and you need to lay a 2-core wire from the front hub to the lights (usually the front light has a switch that the front and the rear light on & off).

It was quite easy to remove the original one core piece of wire to replace it with a  2-core one: I drilled into the rear of the light through the 1-core wire and also removed all the tar that was used to seal the unit and make the lightbulb holder stay in place.

Next step was looking into how to replace the lightbulb with an LED. LEDs on a bike are advantageous over incandescent lightbulbs because they are absolutely immune to vibrations (there is no filament to break). Incidentally they consume a lot less current but that’s not something you worry much unless you power them out of batteries.

Generators (dynamo) are AC generators. Their output tension is not regulated (the faster you cycle the more energy they produce) so I had to think about voltage and current regulation before using LEDs.

Here is a diagram of the circuit I built and managed to fit inside the 597 (these lights are small!).

The circuit can be broken down in to the following elements

1. The hub AC generator
2. The diode bridge that turn AC into DC.
3. The zener diode that limits the tension to 5.5V
4. The 0.47F (yes half a Farad) memory backup capacitor that smoothes the DC tension.
5. The 150mA / 3.3V positive voltage regulator that drop the tension and limits the current in order not to fry the LED
6. A miniature 1uF capacitor to prevent the regulator from oscillating
7. A 30 Ohms resistor to lower the tension down a bit before feeding the LED

The design above has the advantage to give a “stand light” facility. That is to say, when you stop cycling (at a red light for instance), the 0.47F capacitor is charged an keeps powering the circuit. Depending on how much current is draw by your LED the light should stay on few minutes after you have stopped.

Design considerations if you if you want more that one LED:

• Make sure you don’t exceed 150mA of current draw (or use regulators in parallel or a bigger one)
• Make sure there is always a resistor before each LED if you use LEDs in parallel

List of components:

• 4 x silicon rectifier diodes (more or less any type will do)
• 1 x 5W 5.5 Volts Zener Diode
• 1 x 5.5v 0.47F memory backup capacitor
• 1 x 3.3V / 150mA positive voltage regulator (TS2950CT or equivalent)
• 1 x 1 uF electrolytic capacitor
• 1 x 30 ohms 1/4 watt resistor
• 1 x red LED

It should cost you less than £10 to source the parts above. If you are based in London, the people at Cricklewood Electronics should have the components needed in stock!

Bellow are two pictures of the modified Miller 597 installed on my road bike.

Pro audio equipement such as mixers and sound interfaces work with signal levels referenced up to +4 dBu whereas consumer audio equipement (such as hi-fi amplifiers or cd players) works with signals refereced up to -10 dBu.

The following diagram represent a very easy to build transformer that will let you connect the output of a ‘pro’ mix-table to an ‘consumer’ amplifier for instance. Please note that I deliberately left the output to be balanced. You need to make sure the the input of the ‘consumer’ equipment you are connecting the output of this circuit to has a balanced input. If it hasn’t simply connect pins 3 and 1 of the output together to make the line out unbalanced.

Notes: 1 dBu is the voltage level which delivers 1 mW of power in a 600 ohm resistor. dBu and dBv mean exactly the same; dBv came up first but it was confusing people with dBV so dBu is now in use.

I used the following schematics from Jensen Transformers to make the diagram above:

• Jensen pro to consumer interfaces
• Jensen Line input transformer 4:1 stepdown for balanced bridging inputs

I found it very difficult to buy Jensen transformers from UK but luckily I found an alternative with OEP audio transformers (I used an OEP A262A2E wired in 4:1).

Intrinsically, a transformer will not introduce ground loops and other undesirables to your sound path! And it won’t make your sound sound weak like resistor attenuators tend to do.

It would also be very easy to rewire the transformer into a 1:1 configuration if all you need is to de-couple two systems together without introducing ground loops (like in a sound stage to front PA scenario for instance)…

End result with the circuit above (x 2) housed in an aluminium box