Is It Possible to Use Led Without Resistor and Not Burn?

LED's are current operated devices. The voltage dropped across most is in the area of 2.1 Volts. As you and most of the rest of us do not have a current limited 2.1 Volt supply, the standard solution is to apply some greater than voltage to the lamp and limit the current to something below the maximum rated for the particular LED you have selected. So if you might wish to drive it from a 12 V supply, The calculation would go something like 12V-2.1V/0.02A= 500Ohm resistor. The resistor will dissipate about 0.2Watts so a 1/4 resistor will be fine in ambient temperatures will not exceed room temps

1. What led to the rise of the Soviet Union?

The Tsar's government was inept and kept losing.The replacement government was weak. It had been chosen years earlier on an undemocratic franchise.The Bolshevik slogan was 'bread, peace and land'. The existing government could have managed peace and land, but was unwilling to be radical. Still hoped to win the war and acquire Istanbul, the former Constantinople that played a major role in their religious culture

2. Advice me where to buy a led flashlight?

properly i think you pick all of them to illuminate concurrently.... those are the information you may desire to evaluate: a) you may desire to shrink the present to approximately 15mA, the LEDs at the instant are not performing as "load resistors". So for 9 Volt, that must be a 560Ohm (common fee) resistor. b) each and each LED in sequence "steals" approximately 2 Volts away. So with a 9 Volt battery, you may basically have 4-5 LEDs in a row. With a hundred LEDs, you as a result choose 25 parallel circuits with each and each 4 (and a resistor each and each) in sequence. then you definitely choose a transistor which could cope with a 0.4 Amp collector cutting-edge to alter the entire chain

3. Reversed LED in GPIO Output

As shown this circuit cannot drive two LEDs the way you want it. ConsiderThere are however ways to do what you want. This tutorial (source of the figures shown below) has it outlined quite nicely. The circuit looks like this (see last paragraph on the missing current limiting resistor in these schematics, add resistor at your own discretion): Setting the GPIO to input turns off both LEDs. GPIO output, switching high/low turns on either one of them. It is however noteworthy that it will only work if the sum of the forward voltages of the LEDs is higher than the supply voltage (tricks to work around that are in the linked page). Depending on the forward voltages and the supply voltage it is also possible that both LEDs will light up dimmly even if they are not supposed to be on. That is an unfortunate side effect of the strongly non-linear current-voltage characteristics of a LED. At voltages well below their rated forward voltage a small current is still flowing and thus a dim light can be observed.It also requires the forward voltage of each LED to be less than the voltage level of GPIO high (i.e. it will likely not work with white LEDs). It also relies on the fact that the current is limited by the GPIO pin itself (one may or may not choose to go with that assumption). If in doubt use a series resistor at the GPIO pin (see final figure, just skip the additional diodes if working with 3.3V at the Pi).

4. Are led grow lights efficient and effective?

Where did you get the 3-5x more efficient figure? LED are 50% more energy efficient than HPS at least. Chip on board LED is better than 3W or 5W LED with the least amount of light loss. Cheaper LEDs e.g. mars hydro dont last 10 years so they are a poor choice. Buy a COB grow light with a good warranty.

5. What led to the downfall of Windows OS?

What led to the downfall of Windows OS?There has been a downfall of the Windows Operating System? It's still the most used operating system on desktops and laptops, and depending on where you get stats from, Windows still has a commanding presence in the server realm as well. It's so prevalent in fact, that people tend to assume that others are using Windows on their PC.Mobile devices are a different story. In a good majority of the developing world, mobile devices are much, much more numerous than PCs are. Hence why Android is more common in these areas.Windows has not gone anywhere and is not going anywhere anytime soon