Continuing issues with MetroM4 and LED backpacks Moderators: adafruit_support_bill, adafruit

[Blazes946]

Hi there,

Old topic for reference: viewtopic.php?f=63&t=187086

Essentially, I took some time off the project to do other things, make progress on other facets, and return with a clear mind. I redid all the wiring from scratch, new crimping, new soldering, everything. All connections tested with multimeter on the "is connection working if so do a beep" setting. All were individually tested both with spare jumper cables, and with the "wiring" harness I constructed. Zero issues by themselves, either with test "Light one pixel" code I wrote myself and with an LED backpack example in the Arduino library.

When I start to add in backpacks, that's where the issues start. Even just 2 and they often refuse to work. Sometimes it works if I pull out the SCL and SDA cables, reset the board and plug it in, but others, no dice. It's no better or worse with more than 2 backpacks, it's always 1 works flawless, 2+ and it gets flaky.

It's the Metro M4 Airlift Lite, Adafruit 8x8 or 8x16 backpacks + matrices.

Have tried different cables, different power sources, both my PC and a battery pack that puts out 5 volts. I've also tried connected the LEDs GND and VCC to the power pack via a stripped and soldered USB cable, and the board to the PC via the board's mini-USB, but that doesn't light up anything. I'm frankly at my wit's end with how I can't get this stable.

[dastels]

Do all backpacks work as the only one connected?

Dave

[Blazes946]

Do all backpacks work as the only one connected?

Dave

Hi, yep they do.

Something I just noticed in the backpack tutorial:
"You can use these with a 3.3v or 5v microcontroller. Just connect the VCC+ pin is the same voltage as the logic on your microcontroller."

I have the VCC/GND connected to 5 volts as that's my power pack's output, but i see on the metro product sheet (https://www.adafruit.com/product/4000) that the logic is 3.3v
If i understand right, can I use an I2C logic shifter (https://www.adafruit.com/product/757) to bump up the SDA and SCL voltages to 5v, thus matching the power and fix the issue? A friend told me that if the logic voltage is too low the board tends to freeze, which it seems to be doing as it turns on then just kinda sits there.

[Blazes946]

Well I'm pleased to report that it works 100% perfect now. Putting in the I2C level shifter instantly fixed it.

If it's not presumptuous to suggest: Might be something to include in the backpack tutorial since the new microcontrollers use 3.3v logic but the backpacks like it at 5, so a shifter can be of help.

[dastels]

Excellent.

Why not just power the backpack with 3.3v as suggested in the bit you quoted from the tutorial? The biggest disadvantage I think of is that the brightness will be lower which may be an issue depending on use. That said, an I2C level shifter does the job at the cost of an additional part.

Dave

[dastels]

Also FYI, almost all modern MCUs use 3.3v logic.

Dave