The Tech Blog

Back to Basics: Color E-Papers and its Working

Posted under Back to Basics, Educational, Technology on June 16th, 2024 by Amaldev

E-papers/E-ink displays are something most of you would be familiar with. These ultra-low power displays mimic the appearance of ink on paper. They reflect light like paper and get better for reading when there is more surrounding light, unlike any other electronic screens. They don’t need power to retain the image on a screen and have a 180-degree viewing angle. So how do they work?

Think of these displays as small wells with transparent electrodes containing a transparent viscous fluid with charged particles of 2 colors, white(-ve) and black(+ve). Now if you apply a voltage to this well with the top being -ve and the bottom +ve, the black particles get attracted to the top & white goes to the bottom. Now remove the power, the black stays on top with no power needed as the suspended liquid is viscous. This is a classical 2 color e-paper that you see in Amazon Kindles.

Now the original manufacturers of E-ink launched something amazing very recently. A multicolor display that can display up to 60,000 colors. It’s called Spectra 6 and Samsung is launching a whole line up of massive-sized screens for outdoor ad display screens.

So how do these work? It’s an estimated guess as I can’t find much literature on it. They contain Red(+), Blue(+), Yellow(-), White(-) particles. Now how can it display any color on screen with these particles? These particles are of different sizes and quantities in a single well. Now when a variable voltage is given, it takes more time for a larger particle to come up on top than the smaller ones, That’s the secret sauce. Now apply different sequences of voltage to mix and match particles to display true colors, all without continuous power.

The main drawback is slow refresh rates; full-color models take up to 12s for image changes, making them ideal for static content. Think about the use cases. Refreshable Mall Displays where you currently print and paste. Grocery store price tags which change with time. Bus stop signs that run on solar with these low-power displays. Truly displays of the future!

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Tech Explained: Single vs Dual Cell Phone Batteries & Charging

Posted under Educational, Technology on June 9th, 2024 by Amaldev

Fast Charging is a rage these days on mobile phones with companies claiming mad charging rates of nearly 240W. How do they pump this amount of power into batteries?

Most consumer phones that you see out in the wild will be a single-cell type mostly a variation of Lithium based battery as it packs the highest energy density. The battery’s nominal voltage will be in the range of 3.5V to 3.8V depending on the type of chemistry of the cell. The battery capacities can range from 3500mAh-6000mAh. Batteries can be charged at only certain current rates at a voltage slightly above nominal voltages. A higher charging current means more heat. Heat is something really bad for batteries. So phone designers cannot keep increasing the charging current on batteries with a single cell. So what’s the workaround here? Dual Cell batteries…

These are multiple cells wired in series or parallel. Now for series cells, the overall battery voltage is higher so effectively you can charge the cell at a higher voltage and a lower current to reduce your current ratings and losses. Now in series configuration, the internal battery resistance does add up to give a bit more loss. In the parallel config, the voltage remains the same, but you can drastically increase the current as you have 2 parallel paths for currents going into each cell. You can even have 2 separate charging circuits and can effectively double the charging speed by charging both cells simultaneously but this is rarely practiced as it is expensive for the circuit’s POV. For charging wattage claimed over 120W, you usually see a dual-cell setup.

While dual-cell batteries charge faster, they need advanced systems for balanced charging and discharging. They also occupy more space than single cells of the same capacity. So as with anything in life, it’s always a balancing game for a design engineer. An ideal goal is always to determine what power I can pump into the battery maintaining a reasonably small temperature rise. That’s the beauty of engineering!

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