So even when running at 3.3V you could get as little as 2.9V out of an IO pin. While the imp is nominally set to deliver 3.3V, its output won’t be exactly that but in the range VDD-0.4V. What about in between? It could be either, so we want to make sure that our signal always swings below V_IL and above V_IH. So any voltage 3.5V and up will be recognized as a 1 and any voltage below 1.5V will be a zero. So if we set the power rail to 5V, then V_IH = 3.5V and V_IL = 1.5V. The WS2812b chip in a NeoPixel specs V_IH = 0.7 * VDD and V_IL = 0.3 * VDD. Likewise, V_IL is the highest voltage that will still be a 0. Basically, V_IH is the lowest voltage that is guaranteed to be recognized as a High. Since a voltage is an analog value, chip makers specify two values, Voltage Input High and Voltage Input Low, abbreviated V_IH and V_IL, to tell you whether the chip will interpret a given voltage as High or Low. Most digital chips use a voltage level to represent the two digital states 1 and 0, or High and Low, respectively. ![]() ![]() How can this voltage gap be bridged? There are a couple of options which you choose will depend on the needs of your product. All imps are designed to operate at 3.3V. NeoPixels are designed to be driven by a 5V supply. Here we’ll focus solely on how you integrate NeoPixels into an imp-based product. Adafruit has a wealth of guidance for working with NeoPixels, and you should read its ‘NeoPixel Überguide’ before adding them to your project. It’s worth stating up front: NeoPixels are delicate items, sensitive to both static electricity and to voltage spikes. NeoPixels come in strips, on shaped boards and even individually You supply the controller with the intensity values you want relevant LEDs set to, and it lights them accordingly, handling the pulse-width modulation duty cycles for you. The NeoPixel combines the controller with three individual LEDs, one red, one green, the other blue. They are small enough to be supplied in semi-flexible strips or to be pre-mounted on a wide variety of circuit boards, yet smart enough to be individually addressable, giving you full control of the color of each NeoPixel in the group. NeoPixels ™ are what component maker and seller Adafruit calls RGB (Red, Green, Blue) LEDs with integrated controllers, specifically the WS2811 and WS2812 parts produced by World Semi.
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