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Arduino Current Sourcing for Common Anode RGB Answered


Question:
Is it safe for the arduino to sink more current then the arduino is sourcing? (see diagram below)

My project requires 12 of large 10mm RGB leds,  broken down this is 36 leds in total, which exceeds maximum draw,  the design calls for the LED's to share a 5v+ from a seperate 5v regulator, then sink each pin to low to turn them on


is this correct?

Comments

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0
iceng
iceng

4 years ago

A nice drawing deserves another...

Be sure to click the pic, to view the whole image.

ResistorLED.JPG
0
iceng
iceng

Answer 4 years ago

A 5V emitter follower common cathode LED version

COLOR-LED-EMITER-FOLOWERS.PNG
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steveastrouk
steveastrouk

Answer 4 years ago

OK, if you have the head room on the drive to overcome the load drop.

0
iceng
iceng

Answer 4 years ago

Cant imagine the OP will respond or even knows what is happening..

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iceng
iceng

4 years ago

Maybe you seek a lower power driver like a MOSFET with resistor adjustment for each LED Forward Voltage.

Be sure to click the pic, to view the whole image.. -.-. . --. -.

RGB NFET.PNG
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seandogue
seandogue

4 years ago

Ideally, you want to ~isolate the Arduino's I/O circuitry from real world loads by using an intermediary circuit for driving loads.

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Downunder35m
Downunder35m

4 years ago

It does not really matter which way you look at it if you look correctly.
An Arduino is a microcontroller but not a power switch.
That mean logic levels only but nothing to power things up.
All pins on most Arduinos are designed for little electronics projects and if you check the Arduino Playground you will realise that everything else runs through transistors/mosfets and external power supplies.
Create a nice matrix for your LED's and reduce pincount this way.
Then use suitable transistors and current limiting for the LED colors and you are good to go.

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steveastrouk
steveastrouk

4 years ago

Depends on the current, which you don't state. Not only is there a PIN limit, there is a port limit, and a PACKAGE limit which mustn't be exceeded.

Broadly, you must sink NO more than 40mA per pin ABSOLUTE MAX, and happier to stay at 20mA, and NO MORE than 200mA, all up, on all pins.

The best way to do this is to use drivers designed for it, like the ULN2803

0
iceng
iceng

Answer 4 years ago

+1