4 LED matrices off one backpack?
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4 LED matrices off one backpack?

by Misterjenkins on Wed Mar 20, 2013 8:26 am

Hello, I am beginning my first raspi project, which will be 4 LED scoreboards, all displaying the same pair of numbers (the score for player 1 and the score for player 2, repeated 4 times in different locations)

I'm thinking I could use the 8x8 backpack matrices with the i2c output. The scores won't go beyond 10, so I will be able to display all the numbers I need with the matrix, which will have the old scool mini lightbulb look I'm going for (rather than 7 segment).

1. If I go this route, Can I just connect all the similar matrix pins (for the player one displays, for example) in parallel? I have a feeling I need to make some adjustments.

2. Is there a more efficient solution than using all these backpacks? Seems to me I would be overdoing it since I really just need 4 duplicate "dumb" displays all using the same logic. Maybe I could wire 4 matrices off of one backpack?

Thanks all! Love the site. Learning a lot here.
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Re: 4 LED matrices off one backpack?

by adafruit_support_bill on Wed Mar 20, 2013 9:36 am

The problem with wiring them all in parallel is that the led driver chip on the backpack isn't designed to deliver that much current.
What you can do is to give all the backpacks the same I2C address. That way you only have to write to one address to send the same data to all the displays.
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Re: 4 LED matrices off one backpack?

by Misterjenkins on Wed Mar 20, 2013 2:56 pm

Thanks. Makes perfect sense
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Re: 4 LED matrices off one backpack?

by Misterjenkins on Sun Jul 07, 2013 11:39 am

So I've now got 8 1.2" 8x8 matrices with backpacks. 4 use one I2c address, and 4 use another. I also am adding 4 0.56" 7 segment displays with backpacks (using a third i2c address).

Now I'm worried about power draw. As of now, I have used the raspberry pi's 3.3v pin output to power the displays, but only one at a time. What would you recommend so I can light these all up simultaneously?

I'm guessing I need a 3 amp 3.3v supply, but since that might not exist, I could get a 5v supply and use a level shifter. Am I on the right track? How much current can your level shifters handle?

Thanks
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Re: 4 LED matrices off one backpack?

by adafruit_support_bill on Sun Jul 07, 2013 12:03 pm

There are two ways to approach it:
1) power them all from a 5v supply and use an i2c cpable level shifter: http://www.adafruit.com/products/757
2) use a 5v 2A supply with one or more 3.3v buck converters: http://www.adafruit.com/products/1066 You could use one converter for each group of 4 displays.
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