Are my LEDs being undervolted?

Other Hardware LEDs and Multiplexing
1

I have a series of 8x8 LED matrices with MAX7219s wired up to an Arduino UNO. When I measure across the vcc and gnd I'm getting about 3.5v, they all light up and behave normally but I'm noticing that going to a brightness on any intensity over an 8 or so looks the same.

I'm thinking I have them connected to the power in a way that isn't working. They are in 2 chains of 6 and 5, each chain is in series and the two chains are connected to the same power wire on a usb battery. The Arduino is connected to the same battery pack on it's own line. I've mocked up a crude paint picture. The blue, yellow, and green lines are the data pins since ledcontrol can only handle 8 at time I split it between the two.

ledsetup
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My initial thought is that the two strands in parallel are splitting the voltage, would it be better to run the power in series through them all? Or would it be better to give each it's own usb plug?

2

So, not normally?

These sound like you are confusing LED matrix with WS2812.

Label everything in your drawing. If "paint" is too unforgiving, pen-and-paper will do.

3

They aren't flickering, loosing connection, being otherwise inconsistent.

And no, its 11 individual led matrices chained together, one in a set of 6 and another in a set of 5. Each set has the 5 pins connected in series. The data pins go to the Arduino and the power goes to external power.

ledsetup
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Here's with more labels if that helps you.

4

What is the rating on your battery? It sounds like it can't supply the current. Using a typical segment current of 40ma you need 40ma x 8 segments x 11 displays = 3520 ma worst case. Can your battery supply 4 amps?

5

Hi, @dveagle74
Welcome to the forum.

USB battery should be outputting 5V.
What size is the USB battery?

Rather than undervolted, you may be OVERLOADING the USB source.

What happems if you disconnect half of your total display?

Tom.... :smiley: :+1: :coffee: :australia:

6
Model RP-PB172
PD Input 5V2A, 9V2A, 12V1.5A
Input (IN 1) 5V2A, 9V24,12V 1.54
Input (IN 2) 5V2.1A
PD Output 5V3A, 9V2A, 12V1.5A
QC Output 5V3A, 9V2A, 12V1.5A
iSmart Output 5V2.4A
Total Output 5V3A Max
Rated Capacity 5500mAh/66Wh (12V1.5A)

These are the specs of it I believe, if this one wouldn't work what should I be looking for?

7
Model RP-PB172
PD Input 5V2A, 9V2A, 12V1.5A
Input (IN 1) 5V2A, 9V24,12V 1.54
Input (IN 2) 5V2.1A
PD Output 5V3A, 9V2A, 12V1.5A
QC Output 5V3A, 9V2A, 12V1.5A
iSmart Output 5V2.4A
Total Output 5V3A Max
Rated Capacity 5500mAh/66Wh (12V1.5A)

Here are the battery specs, I haven't tested disconnecting half of them yet as I'd have to unsolder some connections.

8

Hi, @dveagle74
You only have to reply once to us as we can all see your answers to posts.

Thanks for the info.
Tom.... :smiley: :+1: :coffee: :australia:
PS. I'm off to work, Hi Ho Hi...

9

Ahh, haven't used this forum until recently.

10

So you can see the battery isn't up to the job. Maybe use 2 of those batteries, it's a natural fit in any case.

11

I'm surprised it takes so much to power these led matrixes. I knew I was running into power issues after I originally tried to power them from the arduino directly

13

That remains to be seen.
What is the value of Rset on the MAX7219?

Are you using a module like this?

image
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or
image
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14

Each LED is a separate component. able to draw say 0.025A.
So 8 x 8 = 64 LEDs

If you turn them all ON, and it is possible.
64 x 0.025 = 1.6 Amps per 8 x 8 display.

Tom.... :smiley: :+1: :coffee: :australia:

15

@dveagle74 Just in case you don't recognize it, that is MORE power than some 5V wall warts deliver. Most are probably closer to 2A so you may get lucky.

16

Looks like it says 103, so 10k. Measuring it seems about right as well.

Yeah, Like the top one.

Maybe about half of them are on. If that many at all

The weird thing I've seen similar setups wired straight to a nano with less issues.

17

Well that is wrong because it is a multiplexed display so only one row (column) can be active at a time.

I don't see a ground connection between the battery bank and Arduino or to the displays.
How long are the wires between displays in a chain?

18

Which output are you connected to?

19

It's a standard usb cable to the usb on the arduino, so the ground is through that. then the grounds of the leds go to the arduino.

Maybe 10in between the displays themselves, but there is a few feet between the first matrix and the arduino on each chain.

Arduino is on the PD and the leds are connected to the QC.

20

That may be your problem.
If it is indeed a QC (Qualcom Quick Charge) output then it may only work with QC devices. I would connect both the Arduino and LED to the PD output. Use a splitter cable.

21

As @jim-p points out a maximum of 8 segments (or dots depending on the display) will be on at a time. So the max per display would be about 40 ma X 8 = 320 ma. In actual practice it will be somewhat less dependent on the data represented.