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I'm trying to figure out how many MAX7219 8x8 LED matrix can a Raspberry Pi 3 handle without the need of external power.

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I would like to connect an array of 8 but I suspect I'll need an external power. What would be the estimated power consumption with all the 512 LED lights?

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From the 5 V pin, you can draw as much current as your power supply allows, as stated on eLinux:

Maximum permitted current draw from the 5 V pin is the USB input current (usually 1 A) minus any current draw from the rest of the board.

Note that for the Pi 3, the 1 A current input is inaccurate; the Pi Foundation recommend 2.5 A instead. pinout.xyz suggest that "with a decent power supply, such as the official Pi adaptor, you can expect to pull about 1.5A."

The MAX7219 datasheet states that:

Operating Supply Current: TYP 330 mA

So, with 8 LED matrices, you're looking at 330 mA * 8 = 2.64 A, which is probably beyond what your PSU can supply.

Also interesting: the documentation for the LedControl Arduino library, which goes into detail about the hardware decisions you will face. Note that the current draw will depend on the LEDs that you've chosen — as pointed out in the section 'Selecting RSet', if you have LEDs demanding only 20 mA, you'll only have a 170 mA typical draw.

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  • The 330mA typ rating assumes 40mA per LED segment which is maximum brightness. Each segment is cycled on 1/8 of the time but 40mA would still be more than you'd normally need. The MAX7219 is a current source. You put a voltage divider on the I(set) pin to determine brightness and therefore output current. With a 20kOhm resistor it will be approx 168mA all up, with 40kOhm resistor it will be approx 88mA all up. Jun 9 '21 at 5:39
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Here's a good research by user marco_c on Arduino forum where you can see that MAX7219 is not drawing that much power.

http://forum.arduino.cc/index.php?topic=301955.0

It probably depends on different versions/manufacturers of MAX7219 but his draw only 2.6mA with no LEDs turned on and 67mA with all LEDs at maximum brightness. In that case you could easily power 8 pieces of 8x8 LED matrix with max consumption of 0.5A.

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  • That's with an R(set) of 62kOhm, which is a lower brightness setting than all 3 brightness settings suggested in the MAX7219 datasheet. But depending on your needs and type of LED, could well be as much as you need. Jun 9 '21 at 5:42
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Of course, there's no reason why you couldn't power the LED array from a separate power supply. As long as the ground lines are connected there should be no problem and you can simply use a power supply with as much output as needed.

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  • This doesn't answer the question; "I'm trying to figure out how many MAX7219 8x8 LED matrix can a Raspberry Pi 3 handle without the need of external power."!
    – MatsK
    Jul 24 '19 at 10:25

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