led RGB strip

Good morning,

Devo utilizzare degli RGB strip led e guardando in internet ho visto molti circuiti in cui si usano i transistor per connetterlo ad arduino. Qualcuno potrebbe fornirmi una spiegazione sul perchè si usa il transistor in questo caso e in generale :) ( non sono molto esperto in elettronica come potete immaginare)

I have to use RGB strip led and i saw on internet many circuits that using transistor to connect it to arduino. Someone can explain me why is necessary to use transistor in this case and more in general :) (I'm not an expert on elettronic as you can see)

Hi Ioma,

The reason is that if you connect the strip to the Arduino, it would be damaged.

Most rgb led strip need 12V supply. Arduino pins can go to 5.5V maximum.

Also, rgb led strip will need around 20mA per led on each of the r, g & b channels. A strip of 30 leds would need 600mA for each of r, g & b channels. Arduino pins can source or sink 40mA maximum.

The transistors help in 2 ways: 1. they allow a small current from the Arduino pin to switch a large current flowing through the strip 2. they protect the Arduino from the 12V which would damage it.

Paul

Hi loma,

The transistor will be used as a switch which will be activated by the Arduino.

This swich will be connected to a high power that will supply the LED strip. Arduino will not be able to handle this quantity of power due to the 5.5 v 40 milliAmps.

I advice you to see this video: http://www.youtube.com/watch?v=Te5YYVZiOKs

Saroiane

There are LED strips that don't need the (minor) complication of the transistor.

You will still have to POWER the LED strip from "outside" the Aduino's power, and that power MAY be at 12v... and has to be carefully kept separate from the Arduino.

Or you may be able to power both strip and LEDs from one 5v supply... but be sure that the power for the LED strip is going directly to the LEDs, not arriving there "through" the Arduino.

All explained (a 5v only answer) at...

http://www.arunet.co.uk/tkboyd/ec/WS2812SmartLEDs.htm

(The LEDs there are in a rigid ring, but the same LEDs are also sold "made up" as a strip.)

BE SURE TO INCLUDE THE RESISTOR AND THE CAPACITOR.