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Topic: How do I source more than 500ma for my large LED matrix? (Read 1 time) previous topic - next topic

binarymagick

Jan 24, 2012, 05:28 am Last Edit: Jan 24, 2012, 05:31 am by binarymagick Reason: 1
I need to be able to source about 700ma to drive a large 16x16 single color (blue) LED matrix driven by four MAX7221s, Arduino and microSD shield. It seems 9v 650ma wall adapters are very common.

1) Will I be able to safely exceed the 650ma limit on the wall adapter when I briefly have all LEDs on at once? If not, where can I find a higher max current wall supply that will work?

2) How should I wire things so the Arduino and microSD shield are getting the current they need AND the LED matrix and four MAX7221s I'm using to drive it are getting enough current to have all LEDs on at once?

3) Are there any other considerations I'm missing?

What's throwing me for a loop here is the fact that the LED driver and Arduino(and microSD shield) are interconnected. I can't wrap my head around one 5v power supply built in to the Arduino and one 5v power supply going to the MAX7221s when the Arduino is sending data to the MAX7221s. Is this safe, or is there some better way I'm not aware of?

I'm guessing I'll plug the wall adapter into a barrel jack on my own board with the MAX7221s on it, then supply the Arduino with power by splitting from the 9v and ground on my board and connecting those to the Vin and GND pins on the Arduino. Is this correct, or should I approach this some other way?

Please excuse my questions if they are misguided or overly basic. I came from a software background.

majenko

5V is 5V is 5V.  As long as the ground connections are all linked together it matters not where that 5V is coming from.

The simplest way is, as you say, 9V wall wart splitting into 2 legs - one to the Arduino / SD shield, and one via your own regulator circuit to the MAX chips.

I would find it doubtful that running a 650mA power supply at 700mA - especially after the added overhead of voltage regulator - would be a good idea, even for short periods.  At best you will reduce the lifetime.  At worst you will reduce it to a molten blob of plastic and metal. 1A wall warts are quite common.

One other option is to use a high current switched mode power supply - of the kind you get for charging mobile phones and other mobile devices.  These will usually give you 5V directly which can be plugged straight into the USB socket of the Arduino.  A small adapter could break out an extra 5V line before the USB socket on the Arduino to power your MAX chips.

Donziboy2

Ok, first Id love to know how your pulling that much from just 4 MAX7221's since i run a 1x5 matrix on 5 MAX 7219's thats 320 leds and it only pulls at most 200-250mA at 5V from an old Dlink wallwart I have.  The 72xx series is supposed to blink the led's at a high freq that reduces the overall power needs of the matrix.

Second, a 9v and 650mA wall wart is actually rated at 5.85 Watts max....... So at 5v and 700mA you need 3.5 Watts.  Thats well within the range of the 9v 650mA wall wart.

Grumpy_Mike

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a 9v and 650mA wall wart is actually rated at 5.85 Watts max....... So at 5v and 700mA you need 3.5 Watts.  Thats well within the range of the 9v 650mA wall wart.

But only if you use a switching regulator to drop the voltage. With a linear regulator it is a no go.

Chuck4360

If you're talking about how to supply that much current to the LEDs and still be controlled by the Arduino, I have used a sparkfun ROB-09571 motor driver. They have different models that carry different current.  I have driven a 1 amp device with it with no problems.  The model I used has two drivers on it, which will carry up to 2 amps per motor.  Since it has a speed control on it, I guess you can make the LEDs dimmer or brighter also.  It's about $20.  Hope this helps!

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