Hi Albert, I am usingIf you are using a 12V supply as in the video, the resistor should be between 470Ω and 10kΩ to keep the current within a sensible range. Such a resistor will not get too hot with a 12V supply.
I have tried the 200Ω but cant get the LED to turn on as the example, as soon as i connect the green wire LEDs turn OFF.A standard red LED has a forward voltage drop (Vf) of approx. 1.8 V. With a 3 V battery, that leaves 1.2 V across the resistor. For an LED current of 12 mA (a nice safe value), Ohm's Law says the resistor value should be 100 ohms.
Note - the resistor in the video is 470 ohms. With the 12 V source being used, this yields an LED current of around 22 mA.
I am not sure how the person in the video is able to get both LEDs to have same brightness. In my case I only get one LED bright and the other one is dull.It is not a good idea to put LEDs in parallel. They will share current unequally and one may be brighter than the other. Each LED should have their own resistor.
The amount of voltage that a LED drops is first dependent on the color of the LED. It also has a voltage range that it will drop. That parameter is Vf. Call it 2.1 V for a RED LED. There is a typical led current (call it 1 to 10 mA if you don't know.
The resistor is calculated by R=(V-n*2.1)/10e-3 where V is the supply voltage, 2.1 is the drop and 10 mA is the typical operating current and n is the number of LEDs in series.
You can place LED's in series, BUT the variation in Vf might cause intensity variations.
The required wattage of the resistor should be checked. i.e. The resistor should have a higher wattage than calculated and more likely close to a factor of 2. i.e if you get 0.24 W, use a 1W resistor.
It's probably because they don't have the same forward voltage. The one with the lower forward voltage will be brighter.I am not sure how the person in the video is able to get both LEDs to have same brightness. In my case I only get one LED bright and the other one is dull.
You are right, put in brand new two LEDs and they are both same brightness. Thank you!!!It's probably because they don't have the same forward voltage. The one with the lower forward voltage will be brighter.
by Jake Hertz
by Jake Hertz