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  • LaurJ commented on nqtronix's instructable Practical Guide to LEDs 1 - Pick your LED!2 months ago
    Practical Guide to LEDs 1 - Pick your LED!

    "This works because a CR2032 can not provide enough power to destroy an LED." is the explanation. He also mentions on a later page that the reason is the internal resistance of the CR2032 battery, which is enough to limit current. In fact, your statement that "...you can connect an LED to a power source AS LONG AS the power source's voltage is limited to slightly below the LEDs running voltage...", while not wrong, does not explain the situation here. It's possible to run a red led with a forward voltage drop of 1.8 V from the 3V CR2032, because the voltage (or more precisely, emf) is not enough to characterize the behaviour of a power source in the face of a load.

    App note? You mean my notes from the University? :D

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  • LaurJ commented on nqtronix's instructable Practical Guide to LEDs 1 - Pick your LED!2 months ago
    Practical Guide to LEDs 1 - Pick your LED!

    A technical optoelectronics note about the need for a plastic encapsulation: While the dome's shape can be modified to alter the final light distribution, the need for encapsulating the chip at all (besides mechanical protection) is due to the fact that the refraction index of the semiconductor material is very high. The plastic acts as a middleman (compare RF impedance matching by quarter-wave transformer, although here there's usually no "quarter-wave" about it), with a refractive index roughly the geometric mean of the ones of the semiconductor and air. This maximizes light transfer from the chip into air. Without it, much more of the light would be internally reflected back into the chip at the semiconductor-air interface, and since the semiconductor also has high absorpti...see more »A technical optoelectronics note about the need for a plastic encapsulation: While the dome's shape can be modified to alter the final light distribution, the need for encapsulating the chip at all (besides mechanical protection) is due to the fact that the refraction index of the semiconductor material is very high. The plastic acts as a middleman (compare RF impedance matching by quarter-wave transformer, although here there's usually no "quarter-wave" about it), with a refractive index roughly the geometric mean of the ones of the semiconductor and air. This maximizes light transfer from the chip into air. Without it, much more of the light would be internally reflected back into the chip at the semiconductor-air interface, and since the semiconductor also has high absorption, would be rendered into heat, reducing the efficiency of the LED. In fact, this is still one of the largest obstacles in achieveing higher efficiency.

    You likely will not get away without wiring at least one wire for each LED group (the LEDs that will be on at the same time), plus one common wire for the cathode. Assuming 10 groups, each group will have 20 LED-s, and using 20mA (the most common, and can be reasonably bright) LED-s that's 400 mA of current. With AWG 22-24 wire, at the end of the 100' you'll have around 1 V of voltage drop, so you need to consider that when adding current limiting resistors to the LED-s and selecting your power source. Double that, to include the cathode wire resistance, now that I think of it.Also, the cable will cost some. From farnell, if you buy by 100m or 50 m, you'll get around 1.5€/m for 12-core 0.22mm2 (~24AWG), plus shipping.For controlling, I suggest either a 555 circuit with a potentiome...see more »You likely will not get away without wiring at least one wire for each LED group (the LEDs that will be on at the same time), plus one common wire for the cathode. Assuming 10 groups, each group will have 20 LED-s, and using 20mA (the most common, and can be reasonably bright) LED-s that's 400 mA of current. With AWG 22-24 wire, at the end of the 100' you'll have around 1 V of voltage drop, so you need to consider that when adding current limiting resistors to the LED-s and selecting your power source. Double that, to include the cathode wire resistance, now that I think of it.Also, the cable will cost some. From farnell, if you buy by 100m or 50 m, you'll get around 1.5€/m for 12-core 0.22mm2 (~24AWG), plus shipping.For controlling, I suggest either a 555 circuit with a potentiometer to control the speed (if you want to eyeball it) or some cheap MCU if you want to dial in an approach speed at a few-% accuracy (at which point you don't really need the 4017 sequencer).

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  • LaurJ commented on geekrex's instructable How to salvage a DVD Drive For Free Parts4 months ago
    How to salvage a DVD Drive For Free Parts

    yes.

    Running a speller is easy and you aquire new knowledge of the language used. While it's true that current context doesn't require good form or ortography, there might come a situation (an internship application, perhaps) when one is evaluated on their capability to express oneself correctly. It's good practice to keep some standards in your language.Furthermore, don't you find that accusing someone of being a nazi is a bit extreme? Raymond pointed out a spelling error, and suggested a method to avoid them in the future. He didn't go to the guy's home and demand him to check and correct all of the text at gunpoint.

    It seems I do, yes ='D

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