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I am trying to determine the total pin power requirements for my Mega 2560 project; it will connect to 3 1m Neopixel strips and 5 RGB laser fiberoptic lights, and control them via PWM. Each strip and light will have its own external power supply. The laser lights will be controlled by an Adafruit TLC5947 LED Breakout board with 3 (R,G,B) inputs. Further, each laser light is turned on by a logic high command.

My questions are: How can I determine the total pin outputs? Can all this be controlled safely from the Mega, or will I need to add transistors? I have read 200mA is the maximum for the Mega, however I have found a seemingly definitive post on Arduino.cc that states 800mA is the maximum. https://forum.arduino.cc/index.php?topic=327742.0

here's my rough schematic: enter image description here Thank you in advance!

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Neopixels only need a control signal and Gnd when powered externally - connect the external power supply Gnd to the Mega Gnd as well.

The 2560 chip can definitely work with 800mA (200mA per VCC & Gnd pin, and there are 4 of each). The onboard supply can't cope with that - you get a max of 500mA from USB (due the 500mA PTC fuse, the big gold or green part next to the USB connector), or something under an 1000mA depending on how 5V is created. 12V into the barrel jack and high current will over heat the 5V regulator. 7.5V into the barrel will give you a better shot at high current. Then there is 1V rated reverse polarity protection diode between the barrel jack and the regulator. You can't put 5V into the barrel and get 5V out, you need to overcome the diode and the regulator. 7.5V wallwarts work well for that. www.dipmicro.com used to carry 7.5V/1A wallwarts, I don't know if they still do. If you decide to use an external 5V source via the power header, then the power headers are only rated for 1A current as well.
I use this one for 5V projects, 4A to power the Arduino, make yourself a power cord splitter and have 5V for other stuff as well direct from the wallwart, and not off the Mega board.

Are the lasers controlled by current into the R,G,B pins, or are they externally powered and R,G,B are just control signals? If their power comes from RGB, then you'll also want to power the TLC5947 seperately and just connect control signals and Gnd to the Mega.

  • Thanks Crossroads, this is very helpful. The lasers will be powered externally as well, so R,G,B are just control signals. My confusion was whether or not the pin outs were drawing 40mA if they were just signal, and it seems like the answer is no. Given that the peripherals are all powered externally, will 5V power work, or should I use 7.5V? – David W. Feb 7 at 22:16

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