tutorials:learn:arduino:leds.html
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tutorials:learn:arduino:leds.html [2010/11/10 00:30] ladyada |
tutorials:learn:arduino:leds.html [2016/01/28 18:05] (current) |
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| - | The first two rows talk about the 'wavelength' - this is a specific way of indicating the color. After all, 'super bright red' is a very subjective description. [[http://eosweb.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html|With the wavelength, we can know exactly what color is emitted.]] \\ The third row is basically saying 'how much does the color vary from the wavelength' \\ The forth row isnt so important, we'll skip that | + | The first two rows talk about the 'wavelength' - this is a specific way of indicating the color. After all, 'super bright red' is a very subjective description. [[http://science-edu.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html|With the wavelength, we can know exactly what color is emitted.]] \\ The third row is basically saying 'how much does the color vary from the wavelength' \\ The forth row isnt so important, we'll skip that |
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| <class warning> | <class warning> | ||
| - | **Whenever using an LED, make sure to __always__have a resistor! The resistor //limits// the current, which will keep the LED from burning out! \\ ** | + | **Whenever using an LED, make sure to __always__ have a resistor! The resistor //limits// the current, which will keep the LED from burning out! \\ ** |
| </class> | </class> | ||
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| <class white>This is a KVL question. 9V = 2.2V + Vresistor so Vresistor = 6.8V </class> | <class white>This is a KVL question. 9V = 2.2V + Vresistor so Vresistor = 6.8V </class> | ||
| **Now that you know the voltage, how much current (I) is going through the 1,000 ohm resistor (R)?** \\ //Highlight the text below to see the answer //** ** | **Now that you know the voltage, how much current (I) is going through the 1,000 ohm resistor (R)?** \\ //Highlight the text below to see the answer //** ** | ||
| - | <class white>We determined the voltage (V) is 2.8V, we use Ohm's Law I = V/R = 6.8/1000 = 0.0068 Amps = 6.8 milliAmps </class> | + | <class white>We determined the voltage (V) is 6.8V, we use Ohm's Law I = V/R = 6.8/1000 = 0.0068 Amps = 6.8 milliAmps </class> |
| **Next, we will examine the 5V-powered LED. The forward voltage is 2.2V, what is the voltage across the resistor?** \\ //Highlight the text below to see the answer //** ** | **Next, we will examine the 5V-powered LED. The forward voltage is 2.2V, what is the voltage across the resistor?** \\ //Highlight the text below to see the answer //** ** | ||
| <class white>Another KVL! 5V = 2.2V + Vresistor. Vresistor = 2.8V </class> | <class white>Another KVL! 5V = 2.2V + Vresistor. Vresistor = 2.8V </class> | ||
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| - | Use a 10K potentiometer for this excersise, find one that has **104** printed on it (this is the same as 1.0 (first two digits) with 4 zeros afterwards = 10,000) | + | Use a 10K potentiometer for this excersise, find one that has **103** printed on it (this is the same as 10 (first two digits) with 3 zeros afterwards = 10,000) |
| {{ http://www.ladyada.net/images/arduino/LEDs/potadjust.gif?nolink&638x510 |}} | {{ http://www.ladyada.net/images/arduino/LEDs/potadjust.gif?nolink&638x510 |}} | ||
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| - | <class style3>Last Quick Quiz!</class> \\ **How much current is flowing through the LED when the pot is turned down?** \\ //Highlight the text below to see the answer //** ** | + | <class style3>Last Quick Quiz!</class> \\ **How much current is flowing through the LED if when the pot is turned down? The forward voltage of the LEDs are 2.2V.** \\ //Highlight the text below to see the answer //** ** |
| - | <class white>(5V - 2.2V) / 100 ohm = 28 milliamps </class> | + | <class white>2.2V / 100 ohm = 22 milliamps </class> |
| **What about when the potentiometer is turn all the way 'up'?** \\ //Highlight the text below to see the answer //** ** | **What about when the potentiometer is turn all the way 'up'?** \\ //Highlight the text below to see the answer //** ** | ||
| - | <class white>(5V - 2.2V) / 10100 ohm = 0.27 milliamps </class> | + | <class white>2.2V / 10100 ohm = 0.217 milliamps </class> |
| Whew, that was a long and very math-intensive lesson. We'll get back to doing more with software and fun blinky in future tutorials, but we hope that this tutorial helped you understand some of the details of how to wisely use LEDs! | Whew, that was a long and very math-intensive lesson. We'll get back to doing more with software and fun blinky in future tutorials, but we hope that this tutorial helped you understand some of the details of how to wisely use LEDs! | ||
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