Hello, I know how to wire LEDs in series and parallel. I have 5mm LEDs that came with an Arduino kit that I have bought. When I am using the 5v pin and ground I can't even power more than 2 LEDs in series. When I used a 6v power supply it worked a little better, but shouldn't I be able to power more than 2 LEDs in series with the Arduino 5v? Can someone explain? thank you
Are you using current limiting resistors?
Vf for a typical LED is . . . ?
How many times does that go into five?
Thanks, Awol, it makes sense when you put it like that. When I use 2 of the LEDs that came with my Arduino kit it works. But when I try to use these 2 super bright LEDs I bought from Adafruit it does not work because each LED has a 3.2 forward voltage. Super Bright Blue 5mm LED (25 pack) : ID 301 : $8.00 : Adafruit Industries, Unique & fun DIY electronics and kits
aarg:
Are you using current limiting resistors?
I tried it both with and without but I may have been using the wrong resistors, maybe you can help me. I have a 5v power supply from Arduino. The LEDs I'm using have a 3.2-3.8 forward voltage. I cant get more than one to work in series. Would adding resistors help that problem? Thank you for response
tjones9163:
I tried it both with and without but I may have been using the wrong resistors, maybe you can help me. I have a 5v power supply from Arduino. The LEDs I'm using have a 3.2-3.8 forward voltage. I cant get more than one to work in series. Would adding resistors help that problem? Thank you for response
No adding resistors in series with two LED's would not help. Adding a resistor in series with one LED is to prevent too much current from flowing and hurting or burning out the output pins on your Arduino.
At 3.2 volts you can only use 1 LED on each output pin - just not enough voltage
saildude:
No adding resistors in series with two LED's would not help. Adding a resistor in series with one LED is to prevent too much current from flowing and hurting or burning out the output pins on your Arduino.At 3.2 volts you can only use 1 LED on each output pin - just not enough voltage
So pretty much im being limited by my voltage supply? so with the Arduino 5v pin and LEDs with smaller forward voltages like 2.2, i can only power 2 LEDs max? and the resistor would affect the brightness? Thanks for response
The 5V limit keeps the Arduino from burning up.
If you want more LEDs in series, then you need to add something that can handle higher voltages.
TPIC6C595 or TPIC6B595 is good for that - you shift in data, and the 8 outputs can handle higher current from up to a 33V ('6C595) or 50V ('6B595) supply.
You can power several 'strings pairs' of LEDs & resistors, just keep the total current to a safe level.
Let’s say you only need 5ma to light your LED.
If the maximum current allowed is 20ma, you can drive 4 of these LED resistor pairs.
.
You can also use a switching transistor similar to @CrossRoads above but one transistor per Arduino pin,. Or use a chip like a UNL2803A - Darlington array. One pin will expand to at least 8 on the UNL2803A - it will also handle up to 50 volts on the output so you can use more than one LED in series on each output
larryd:
You can power several 'strings pairs' of LEDs & resistors, just keep the total current to a safe level.Let’s say you only need 5ma to light your LED.
If the maximum current allowed is 20ma, you can drive 4 of these LED resistor pairs..
by sting pairs do you mean something like parallel circuit? In which each branch would be carrying 5ma?
tjones9163:
by sting pairs do you mean something like parallel circuit? In which each branch would be carrying 5ma?
Yes
