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Archive for September, 2011

Webkit-based UI for TV devices

Thursday, September 15th, 2011

Netflix’s Webkit-based UI for TV devices article says that Netflix uses WebKit, JavaScript, HTML5, and CSS3 to build user interfaces that are delivered to millions of game consoles, Blu-ray players, Internet-connected TVs, and devices.

Matt McCarthy and Kim Trott, device UI engineering managers at Netflix, have just published 50 presentation slides from their recent talk at OSCON 2011 in which they explained how Netflix develops its Webkit-based user interfaces. The slides are accompanied by detailed speaker notes.

This stuff is interesting because of the challenges of developing the interface for a wide variety of platforms with vastly differing capabilities. Different platforms have different needs and capabilities. In the slideshow, they acknowledge there are differences between platform UI needs, but they seem to try a one-size-fits all approach.

I saw this slide set first mentioned at Inside Netflix’s WebKit-Based UI For TV Devices posting at Slashdot.

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Commonly used AC voltage levels

Tuesday, September 13th, 2011

AC voltage levels:

0.316V The most common nominal level for consumer audio equipment is -10 dBV, 0.316 volts root mean square (VRMS).

0.7746V The reference voltage for the decibel unloaded (0 dBu) is the voltage required to produce 1 mW of power across a 600 ohms load (approximately 0.7746 VRMS)

1V  The reference voltage for the decibel volt (0 dBV) is 1 VRMS, which is the voltage required to produce 1 milliwatt of power across a 1 kilo-ohm load

1.228V The most common nominal level for professional equipment is 4 dBu. A signal at +4 dBu is equivalent to a sine wave signal with a peak amplitude of approximately 1.737 volts,or any general signal at approximately 1.228 VRMS.

12V A low voltage lighting system usually operates on 12 or 24 volts.

24V A low voltage lighting system usually operates on 12 or 24 volts.

24V Used for controlling relay coils in some automation and control systems.

50V Extra-low voltage high limit is 50V AC

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50V Low Voltage Directive is effective for voltages in range 50 – 1000 volts a.c. or between 75 and 1500V DC

75V Typical telephone line ring voltage is 75 V a.c.(20 or 25 Hz), it could be between 40 and 150 Volts (15-68 Hz)

100V Mains voltage in Japan. Reference voltage level used on electrical power stations measurements (100V = nominal high voltage on line being measured)

110V Mains power in USA, the voltage you expect to get from mains outlet
115V Mains power in USA, the voltage you expect to get from mains outlet
120V Mains power in USA, the output voltage on the distribution transformer

200V If the voltage is less than 200 V, then the human skin is the main contributor to the impedance of the body in the case of a macroshock—the passing of current between two contact points on the skin.

208V The voltage you expect to get between two phases in USA in case our apartment
gets two phase wires from three phase transformer (208/120V)

220V Old European nominal voltage, harmonized to 230V

230V Electricity supplies within the European Union are now nominally 230 V ± 6% at 50 Hz

240V the voltage you expect get between two hots in USA on your hous
240V Old nominal mails voltage used in UK, harmonized to 230V
240V the voltage you get between two hots in USA on the distribution transformer

277V Voltage between phase and neutral on 277/480V three phase system, used in USA for example lighting loads on big buildings

400V Voltage between phases on 220/400V three phase system (old European system)

415V Voltage between phases on 230/415V three system (modern European system)

450V If the voltage is above 450–600 V, then dielectric breakdown of the skin occurs

480V Voltage between phases in USA in commonly used 3 phase distribution

600V Three phase power voltage

690V Three phase power voltage used in industry for larger electrical motors (Europe)

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1000V Isolation test voltage for 130V rated working voltage basic isolation (IEC950)

1000V Low Voltage Directive is effective for voltages in range 50 – 1000 volts a.c. or between 75 and 1500 volts d.c
1000V There phase power voltage used on 1 kV power distribution (in use in Finland)

1350V Basic insulation of 1350V rms is needed for test-and-measurement instruments rated at 250V (IEC 61010-1)

1500V Basic insulation of 1500V rms is needed for information-technology products rated at 250V (IEC 60950-1)

1500V Isolation test voltage for 230V rated working voltage (IEC950) (basic isolation)

2100V Isolation test rating for reinforced isolation for 130V rated devices

2300V Use 2300V rms or 3250V dc test voltage for dielectric-withstand test for double insulation

7.2kV Common distribution voltage in USA

10kV Common distribution voltage in Finland

11kV Common distribution voltage in UK, New Zealand and Australia

12.47kV Common distribution voltage in USA

20kV Common distribution voltage in Finland

25kV Electrical trains use 25kV 50Hz power in Finland

33kV Common distribution voltage in UK, New Zealand and Australia

34.5kV Common distribution voltage in USA

110kV Commonly used voltage level on long distance electrical transportation lines

220kV Commonly used voltage level on long distance electrical transportation lines

400kV Commonly used voltage level on long distance electrical transportation lines

Electrolytic capacitor life

Sunday, September 11th, 2011

As we all know, a good LED could last very long up to 50,000 hours with with a good heat sink. But how is the LED driver electronics life? For common LED drivers there is at least one component is very weak. It’s the electrolytic capacitor.

High Bay LED Lighting Driver Heat Dissipation Temperature Test Report article gives some use useful information related to electrolytic capacitor life.

Typical temperatures for the how electrolytic caps are 85°C and 105°C. Usually the life time is 2000 or 3000 hrs at one of the above temperatures. This is how electrolytic caps are specified. But the cap’s life doubles for every 10°C below that temperature. So if you go 40°C below the specified temperature, you gain a factor of 2^4 = 16. 16× 3000 hours = 48,000 hours.

If your LED driver has caps at temperature 80 °C, the LED driver only can last about 2 years or less. After that time you can expect poor performance (lowered capacitance, increased ESR) or even capacitor exploding.

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Stupid Robots

Friday, September 9th, 2011

Ever worry that robots are getting a little too smart? Thankfully, some people are dedicated to keeping our metal friends dumb.

Bacarobo, the Stupid Robot Championship, is a showcase for just such robots. The contest originated in Japan (running in 2007 and 2008) before moving to Hungary in 2010. The competition has three main rules: the robots must operate automatically, they must be useless and they must be funny.

Power Quality Symptoms & Solutions

Monday, September 5th, 2011

Power Quality Symptoms & Solutions e-book is is written from an electronics point of view, rather than a power engineering one. And in so doing, provides the bridge between theory and real life. According to the book introduction more and more lecturers are using this material as a reference in their courses. You can find lots of interesting reading here for many industry fields and links to other resources.

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