Monthly Archives: August 2015

LED Light Guides Equal OLED Performance

The visual impact of OLED panels is hard to resist. Their luminosity is seductively stylish and sleek. Fashion-forward lighting designers prefer the eerily-even silky glow of the OLEDs, even though these are more expensive, have a short lifetime and can be damaged more easily than other light emitting panels. Now GLT or Global Lighting Technologies, with their edge-lit LED-based light guide technology, is about to turn the tables on OLEDs.

The latest product from GLT, a 4×4 inch LED-based light guide, demonstrates this technology specifically. Compared to an OLED panel, the GLT light guide has better durability, higher efficiency, longer life and is cheaper as well.

Applications that would normally use an OLED panel, can easily use the LED-based 4×4 inch square GLT light guide as a more durable and affordable solution. GLT has designed these light guides for use in general lighting applications and they offer diffused light output very similar to that from OLEDs, but at a much lower cost.

Offering enhanced light extraction, the light guide is very thin – only 3.5 mm. The panel itself measures only 2 mm, considerably thinner than products GLT made earlier. When in use, industry standard LEDs will typically light it up from the edges, with only a small frame concealing the LEDs. The current product gives out 250 lumens when fully powered, while the efficiency per watt is over 115 lumens.

GLT produces several types of molded light guides. All the products, including the new 4×4 backlights, are made using an efficient light extraction technology. A high-precision micro-molding process impresses optical features within the light guide. By arranging the features to provide a unique transition area, light spreads uniformly and precisely over each point across the panel. GLT has several standard patterns that they mold into the light guides. They can customize each pattern and meet any application virtually.

GLT develops their light guides in very thin packages and designs mechanical holding features into the backlights. That allows the host application to carry the entire display assembly and if that is not possible, use chip-on-flex or chip-on-glass type of assembly. That helps to reduce the parts count and material and assembly costs.

According to GTL, their light extraction technology delivers better optical performance than that offered by V-groove or stamped, chemical or laser etching and printing processes. Additionally, their process is more repeatable. After having demonstrated their light diffusion technology for a few years, GTL has now incorporated it into some of its high-end lighting products.

With their light diffusion technology, GLT offers a large variety of design options to the luminaire designers. Some of these designs can already be seen in the round 12-inch diameter pendant light. This clever design achieves results remarkably like an OLED. It uses a light guide incorporating LEDs along its inner circumference and they emit light in multiple directions.

Panasonic uses light guides from GLT in commercially available fixtures meant for mounting on ceilings. In the fixture, multiple light guides create discrete distribution patterns. These include spot lighting, downward flood lighting and upward ambient lighting within the room.

Christmas tree Lights with the Raspberry Pi

Although Christmas is still a good four months away, you can always prepare for it in advance. The project uses a tiny single board computer known as the RBPi or Raspberry Pi, but you will need some time to collect other material for the project. You will also need time to iron out software bugs, especially if you are a newcomer to the RBPi and Python programming. Additionally, although the project is meant for Christmas, you can as well use it for decorating any other occasion.

The RBPi in the project drives eight AC outlets connected to sets of light. An RGB LED star adds a dynamic range to the light show with its 25-step programming mode. Another advantage the RBPi offers is its audio out can drive the lights in time with music. With a Wi-Fi connection, you can work on the software from a remote location.

The basic ingredients you require for this project are: an RBPi, any model; an SD card containing the Occidentalis operating system; a USB Wi-Fi adapter; and an eight-channel 5V SSR Module Board. You may also use electro-mechanical relays in place of SSRs, but they will produce noticeably audible clicking sounds when switching, while SSRs are noiseless. If you use the SainSmart SSR module board, each of the eight SSRs is rated up to 2A, which will adequately power a string of lights.

Apart from the basic ingredients, you will also require a bunch of extra items: some jumper wires, JST SM Plug and receptacles; four 8ft pieces of wire; eight extension cords, two power distribution blocks; a power strip; suitable enclosure; and speakers. You will also need a few power supplies: for driving the RBPi and the LEDs – 5V, 3A or greater; and for driving the SSR module – 5V, 1A or greater.

For the star, you can use 12mm or suitable RGB LED strands. With the Adafruit WS2801 chip, the RBPi only has to pulse the LED strand once rather than pulse it continuously to keep the LEDs lit up.

It is advisable to test the RBPi and associated components before connecting the wiring. Do this before setting up everything within the enclosure and you have the advantage of easy troubleshooting. Connect the RBPi to a monitor and keyboard, so you can set the system configuration to start software development.

As the default RBPi installation does not have the necessary libraries for driving the WS2801 LEDs, it is necessary to use the Occidentalis operating system from Adafruit. Follow the steps outlined here for configuring the RBPi to get it working as required. Use GPIO 0-7 on the RBPi for driving the SSR module.

As the RBPi drives the GPIO output high, the SSR connected to that pin switches on. This allows the LED associated with the SSR to light up. Write a simple test program to cycle through all the GPIO pins, setting them high for two seconds each.
After testing for proper functioning, connect the lights to respective SSRs through extension cords, using power distribution blocks to keep the wiring neat. Use cheap night-lights to test the animation program first, since this will reduce your eyestrain.

Helping Encapsulated Modules Keep Their Cool

When you encapsulate an active module, you actually cut off air from circulating and removing heat from around the components by the normal process of convection. That forces heat build-up within the active components, including some passive components as well, leading to possible premature failures. Intersil has now mastered the technology of effectively removing heat away from fully-encapsulated modules. Using their unique thermal design, Intersil is able to design very compact encapsulated modules handling up to 50A.

For example, the ISL8240 from Intersil is a 100W analog module, a step-down power supply with single 40A and dual 20A output in the same design. You can parallel up to six of these tiny modules to get a whopping 240A output. Applications involve LTE base stations and data center servers with design architectures built using several FPGAs, ASICs and microprocessors. Only 17x17mm in size, it is extremely difficult to keep the ISL8240 modules cool while delivering full power. Interestingly, Intersil has already announced another module with single 50A and dual 25A module in the same size.

The efficiency of Intersil’s thermal design was evident at a thermal test conducted with the ISL8240 module delivering 40A as output. The fully encapsulated module showed an impressive 99.6°C maximum temperature. Intersil has an evaluation board for users to try their design – ISL8240MEVAL4Z. The tests were conducted using the evaluation board at room temperature without any air flow.

The secret of the Intersil thermal design is a multilayer PC board. The trick is in placing multiple vias strategically to maximize the thermal performance. If this is done correctly, the design need not use any heat sink or fan.

In addition, the IC is mounted thermally on to a copper substrate. This allows attainment of a low thermal resistance of the order of 8.5°C/W. The multilayer board also has two internal copper planes sandwiched in between. These are connected to the top plane with multiple vias, allowing a low thermal resistance design that can remove the excess heat efficiently from the module. The top and bottom layer of the 4-layer board uses 2 oz. Copper, while the inner board layers are made of 1 oz. Copper. Intersil offers Gerber files to speed up your design time.

Intersil makes the PCBs of FR4 grade board material and copper with small additional amounts of solder, nickel and gold. The board uses vias with a finished hole size of 0.012 inches. For making a via, the initial hole drilled is of 0.014 inches. Plating adds a copper wall of 0.001 inches to the hole. Subsequently, the board is plated overall with an ENIG process, adding about 200µ inches of nickel and 5µ inches of gold on to the outer copper surfaces.

If you consider the thermal resistance of one via to that of the copper in the board layers, it will be seen that the via has a much higher thermal impedance for each layer. However, one via occupies only about 1/5000th of a square inch of the board area. The effect of placing N multiple vias in an area is a reduction of the thermal resistance by Nx times.

The Ripple Rating of a Capacitor

Engineers do not prefer having ripples in their circuits and do their best to minimize its effects. For example, an AC source delivers power to an AC-DC converter that subsequently converts it to a steady DC output. It can be very inconvenient if the output were to have any source AC power appearing on top of the DC output in the form of small, frequency dependent variations. However, ripple may not be considered evil in all cases, as some digital signals could be useful to engineers as a necessary design function. Among these are signals that use changes in voltage levels to switch the state of a device and those generating clock timings.

As capacitors can store charge, they are useful for smoothening ripples in circuits. However, the designer must take care that the peak voltage does not exceed the voltage rating of the capacitor. It must also be noted that since there can be DC bias present in the circuit, the peak voltage will be the sum of the maximum ripple voltage and the DC bias. However, that is not enough for electrolytic capacitors.

Electrolytic capacitors are usually made with aluminum, tantalum and niobium oxide technologies and they have polarity. If the negative voltage of the ripple is allowed to drop below zero, this will cause a connected capacitor to operate under reverse bias conditions. Class II ceramic capacitors used in low frequency applications also suffer from this restriction.

A capacitor functions as a charge reservoir, charging with the rise of the incoming voltage and discharging into the load as it decreases – smoothening out the ripples in the process. Therefore, capacitors will see varying voltage. Additionally, depending on the power applied, the current through the capacitor will also vary, as will the intermittently pulsed and continuous power. This causes resultant changes in the electric field of the capacitor regardless of the incoming form and creates oscillating dipoles within the dielectric material, thereby self-heating the capacitor. Any parasitic inductance or ESL and resistance or ESR contributes to the energy dissipation.

That means a capacitor with low ESR, ESL and DF (dissipating factor), will heat up less than one with a dielectric characterized by high ESR and DF. However, as these parameters also depend on frequency, different dielectric materials offer optimum performance (lower heat generation) over different frequency ranges.

The dielectric in a capacitor is usually very thin constituting only a small amount of the overall mass of the capacitor. Other materials used in the construction also contribute to the heating when considering ripple – capacitor plates being one of the major contributors. Additionally, the conductive contacts also heat up to some degree when the capacitor carries an AC signal or current.

For example, at a certain frequency, if the capacitor with a 100mOhms ESR carries a 1A rms current, the power dissipated internally will be 100mW. If this power is supplied continuously, it will heat the capacitor internally until thermal balance is reached. Since this depends on ESR, the power dissipation is a function of frequency. However, the total thermal management will also depend on the capacitor’s environmental conditions, governing the heating up of the capacitor in an application.

Make the OpenJFX DukePad with a Raspberry Pi

If you are looking for a fun project aimed at making your own tablet computer at home based on the Raspberry Pi (RBPi) Single Board Computer, the DukePad is for you. As software, you will use the Raspbian Linux operating system and your environment will be OSGi-based JavaFX.

You can think of DukePad not as a product but an open-source set of plans and software freely available for assembling your own tablet for which, you will be using off-the-shelf components. At present, the DukePad software environment is only demo-quality, as more importance has been given to making the software for demonstration purpose rather than for real functionality.

Although, for the purpose of this guide, you need to name your RBPi with the host name of “dukepad”, you could have any other name of your choice. In addition, instead of letting the RBPi run X11, which it is fully capable of running, JavaFX will be used and it will take over the entire screen. However, while downloading the software into your RBPi, you may choose either to start up with X, or you could elect to download to your desktop PC and then scp/sftp the files into your RBPi.

To get started, you must set up your RBPi as usual; follow these steps if you do not know how. Setup you RBPi such that you have allotted a generous amount of memory to VRAM, also called graphic memory or Video Core. An even split of 256MB each for VRAM and for system memory is also acceptable. If you only have 256MB in total, you may also get by with a 128MB/128MB split, but you may have to tweak the amount of VRAM that FX will eventually use.

If you have not already downloaded and installed the latest JavaSE Embedded release, you may do so now. You can use either the weekly builds or the official builds, whichever is available. For the RBPi, you will have to look for Linux ARMv6/7 VFP, HardFP ABI. Other versions are not likely to work with RBPi.

For installation, you must uncompress the file you have downloaded and put it in a directory of your choice. A good choice would be to install it in the directory /opt; this will require you to assume the superuser status (root). Once you install JavaSE Embedded, it will include JavaFX as well. To play media, RBPi will need some additional packages. You will also need additional packages for configuring the auto-booting and the splash screen. In case you are not interested in creating a table device and you are simply planning to play with the DukePad software, you may safely skip the splash screen and auto boot instructions.

For the boot-loading screen, you need the “fbi” package and for being able to play media files, you have to download and install the “mpg321” package.

For building the body of DukePad, the CAD files are provided here. They contain the template for laser cutting the acrylics for the body, which is made from material of two thicknesses – 4.5mm and 3mm.