I've tried the Blink example and noticed that my LED barely lit with a 220k ohm. Then I calculated the resistance that should be used for my circuit:
5mm Red LED - 2.6V max. forward voltage, 28mA max forward current
I'm using the 5V power port on the arduino uno.
Olm's Law: R=V/I
R=(5 volt-2.6 volt)/0.028 ampere = 85.7 ohms
Why would the blink example tell me to use 220 ohm.....Oh wait I've been using 220k ohm. Things are working better with my smallest resistor now, which is 4.7k ohm. And for the blue LED no resistor at all.
encryptor:
Oh wait I've been using 220k ohm. Things are working better with my smallest resistor now, which is 4.7k ohm. And for the blue LED no resistor at all.
Yes, 220K is about 1000 times too big. Don't leave the resistor out, it isn't good for the LED or your Arduino.
The blue led asks for a 5V operating voltage. When i use in Ohm's Law R=V/I the voltage is 0 when used with the 5V power supply pin. So I still should use a resistor?
encryptor:
The blue led asks for a 5V operating voltage. When i use in Ohm's Law R=V/I the voltage is 0 when used with the 5V power supply pin. So I still should use a resistor?
There is no resistor built into this high intensity blue LED. On the package it says 5V is typical and 6V is max. How can I increase the voltage to use 6V when I only have a 5V pin? Also, the previous question remains unanswered. Do I need a resistor in circuit which isn't calling for it?
Do I need a resistor in circuit which isn't calling for it?
Yes you always need some sort of circuit to limit current and a resistor is the simplest.
See:- http://www.thebox.myzen.co.uk/Tutorial/LEDs.html
Ignore a member dhenry who will pop up and tell you diffrently, he delights in giving advice that damages peoples machines.
this high intensity blue LED.
So what is the current rating? LEDs of over 50mA or so need a constant current supply rather than a resistor.
encryptor:
There is no resistor built into this high intensity blue LED. On the package it says 5V is typical and 6V is max. How can I increase the voltage to use 6V when I only have a 5V pin? Also, the previous question remains unanswered. Do I need a resistor in circuit which isn't calling for it?
We really need to see a link to your specific led to see what you are working with as it is certainly not just a simple standalone blue LED if it requires a simple 5-6vdc connection.
It says on the front of the package 5 volt, 30mA, 300mcd. Here is the link to this LED. I see in the reviews someone points out this is not really a 5V LED and results show to use 3.5V forward (supply) voltage.
encryptor:
It says on the front of the package 5 volt, 30mA, 300mcd. Here is the link to this LED. I see in the reviews someone points out this is not really a 5V LED and results show to use 3.5V forward (supply) voltage.
As we suspected. I would never trust Radio Shacks 'specifications' on something like this. It appears to be a bog standard blue LED and as such needs to have an external current limiting resistor.
encryptor:
It says on the front of the package 5 volt, 30mA, 300mcd. Here is the link to this LED. I see in the reviews someone points out this is not really a 5V LED and results show to use 3.5V forward (supply) voltage.
WOW what a ripoff, a blue LED should cost you no more than $0.20
Now attach a 220R or so resistor to one end and power it up with 5V. Use a meter to measure the voltage across the LED, this will be somewhere between 2.8 and 3.6V, use this to calculate the resistor value for your required current.
Do I need a resistor in circuit which isn't calling for it?
Your pin's output resistance is there to help.
Most of those leds have 3.5v fwd voltage drop. That means the resistance needed is about (5-3.5)/20ma = 70ohm. Your pin's output resistance is about 50ohm so you are in the right ballpark, without a separate resistor.
You can get some guidence by reading the comments:
I used this LED in a computer case as a power indicator. I had to resort to this when the motherboard's power LED output stopped putting out the proper voltage following a BIOS update.
I recommend using a 68 Ohm 1/8 watt (or more) resistor in series when being driven directly from a 5 Volt constant voltage source, for example from a PC power supply red-black wire pair. When driven directly, as the 5 V forward voltage spec would suggest, the LED gets quite hot, and service life would be expected to suffer because of this. All LEDs need a current limiting resistor, and as far as I can tell, this LED does not have one built-in.
I experimented with 47 and 100 Ohm resistors as well. With a 47 Ohm resistor, the LED still heats up too much for my comfort. With a 100 Ohm resistor, the LED runs cool, but is dimmer than with a 68 Ohm resistor. With a 68 Ohm resistor, the LED still produces a little heat, but the brightness is good. If you can find an 82 Ohm resistor, that might be ideal, but RS does not carry that value. These results suggest that Vf (forward voltage) of this LED is roughly 3.5 Volts, which is typical for a blue LED, not 5 Volts as indicated on the package.