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LED backpack issue with feathers
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Please be positive and constructive with your questions and comments.

LED backpack issue with feathers

by faelys on Tue Sep 21, 2021 9:01 am

Hello,

I have bought the 1.2" 4x7-segment display with the LED backpack, and I intended to use it with a feather.

The display and everything else works flawlessly on my Raspberry Pi Zero, and in the process of figuring out the issue I trimmed everything down to the following minimal code:

Code: Select all | TOGGLE FULL SIZE
import board
i2c = board.I2C()
while not i2c.try_lock()
    pass
i2c.writeto(0x70, bytearray([0x21]))
i2c.writeto(0x70, bytearray([0x81]))
i2c.writeto(0x70, bytearray([4, 2]))
i2c.unlock()


I get the expected result of having the central dots lighted up, most of the time only that though sometime there is some garbage data on the other registers.

This proves that the display works fine, my wire are good, and I can understand a wiring diagram (none of these were obvious before testing).

So I proceeded to try and use it with my feather STM32, and I got an error on the first write. However, this board already has some quirks (see https://forums.adafruit.com/viewtopic.php?f=57&t=183168) and I don't know how to ensure the I2C part of the board works as it should. Moreover, I program this board with Ada Drivers Library, so that's a bit too many unknowns on the line.

I also have a feather M0, with the embedded ATWINC1500 wifi thingy, and I flashed CircuitPython on it (admittedly this was not a good idea, but AFAICT it's still a good circuitpython as long as I pretend there is no wifi chip). So I used the python code quoted above, and it also failed, with "OSError: [Errno 5] Input/output error"

I tried going in REPL mode, and I could confirm that i2c.scan() returns an empty list on the feather M0, while on the raspberry pi it returns a single-item list with 112 (i.e. 0x70).

I wondered whether the USB pin of the feather might not be 5V, so I also tried wiring pi's 5V and GND to the backpack, pi GND to feather GND, and feather's 3.3V, SDA and SCL to the backpack, but it still didn't work.

At this point I have no idea what else to try. Would you have any idea on how to further understand the issue?

Thanks in advance.

faelys
 
Posts: 12
Joined: Mon Sep 13, 2021 1:45 pm

Re: LED backpack issue with feathers

by dastels on Tue Sep 21, 2021 10:23 am

Exactly (which pins are connected to which other pins) how do you have it wired up.

And the Feather's USB pin is connected directly to the 5v line of the USB connector. So, yes, it is 5v unless that you've connected the USB to is not working properly. So you don't need the Pi to power it. That's just complicating things.

Dave

dastels
 
Posts: 7570
Joined: Tue Oct 20, 2015 3:22 pm

Re: LED backpack issue with feathers

by faelys on Tue Sep 21, 2021 11:45 am

In the pi-less setup, I have the following connections, with relative localizations assuming facing the digits of the backpack and facing the feather chip with USB connector to the left and battery connector towards the top

  • backpack SCL (rightmost) to feather SCL (second-to-rightmost on the top row)
  • backpack SDA (second-to-rightmost) to feather SDA (lrightmost on the top row)
  • backpack GND (middle) to feather GND (fourth from the left on the bottom row)
  • backpack +5V (second-to-leftmost) to feather USB (third from the left on the top row)
  • backpack VIO (leftmost) to feather 3V (second-to-leftmost on hte bottom row)

All the connection are made directly with a wire, sold with female connectors on both ends, and I soldered male connectors on the backpack and on the feathers. The same wires are used when connected to the rpi, so I assume they work correctly, and the backpack sordering is good. I don't use a breadcrumb because I soldered the pins upside down, and I didn't see the need when only wires are involved.

I can provide photos if it the text is not clear enough or if my soldering is suspect.

faelys
 
Posts: 12
Joined: Mon Sep 13, 2021 1:45 pm

Re: LED backpack issue with feathers

by dastels on Tue Sep 21, 2021 11:55 am

That's wired correctly. Please post the photos.

Dave

dastels
 
Posts: 7570
Joined: Tue Oct 20, 2015 3:22 pm

Re: LED backpack issue with feathers

by faelys on Tue Sep 21, 2021 12:28 pm

Here is the backpack, along with the colored wired:

Image

Here is the chip-side of the feather, so you can double-check the color match, and you can see the upside-down male connector

Image

Here is the other side of the feather, where my soldering can be seen. I'm a bit disappointed with the quality, the En and USB look especially bad on the photo while in real life I can it clearly cone-shaped (although with less tin than the other pins) and not torus-shaped (which I know is a common wrong solder).

Image

faelys
 
Posts: 12
Joined: Mon Sep 13, 2021 1:45 pm

Re: LED backpack issue with feathers

by dastels on Tue Sep 21, 2021 1:00 pm

The soldering looks good overall, though I'm wondering about the I2C pins. Maybe retouch those and see if it helps.

Dave

dastels
 
Posts: 7570
Joined: Tue Oct 20, 2015 3:22 pm

Re: LED backpack issue with feathers

by faelys on Tue Sep 21, 2021 2:26 pm

I added a bit more tin on the I2C pins, but now that the night has fallen the photos are even worse.

It hasn't changed anything with my problem, there is still no communication with the LED backpack.

What else can I try?

faelys
 
Posts: 12
Joined: Mon Sep 13, 2021 1:45 pm

Re: LED backpack issue with feathers

by dastels on Tue Sep 21, 2021 2:57 pm

It sounds like a problem board.

Please email support@adafruit.com with a link to this thread, your order number, and request the replacement of one 1.2" 4x7-segment display with the LED backpack as shown on the order.

Dave

dastels
 
Posts: 7570
Joined: Tue Oct 20, 2015 3:22 pm

Re: LED backpack issue with feathers

by faelys on Wed Sep 22, 2021 9:49 am

It might be too late, since I have already mail the support, but here is a new data point.

If I don't plug the 5V pin (which was done unintentionally at first), the I2C communication works perfectly. I even get a display of the dots, though the registers related to the actual digits seem ignored. I understand that more voltage is needed to drive these LEDs, so I'm not surprised with that behavior. What I find interesting is that when 5V pin is unplugged, the backpack behaves as I expect, while as soon as I plug it on the feather or on the rpi the backpack goes silent.

Can that help pinpoint where there might be a faulty connection or component or soldering? Can I hope to repair it instead of replacing it?

faelys
 
Posts: 12
Joined: Mon Sep 13, 2021 1:45 pm

Re: LED backpack issue with feathers

by dastels on Wed Sep 22, 2021 12:03 pm

Odd. Vdd powers the breakout (the driver chip as well as the LEDs) while the 3v (I/O) just powers the I2C pullups (so they match the SCL/SDA voltage).

There definitely seems to be something off with the board.

Dave

dastels
 
Posts: 7570
Joined: Tue Oct 20, 2015 3:22 pm

Re: LED backpack issue with feathers

by faelys on Fri Oct 08, 2021 7:54 am

Sorry for bringing back this thread, but I'm still facing this issue, and I have new data points.

I got a replacement display and backpack from the support, and it had the exact same behavior as the old one. I also got a replacement feather STM32 because of https://forums.adafruit.com/viewtopic.php?f=57&t=183168, and with that new one both displays work flawlessly, just as they both do with my raspberry pi zero.

I also bought another feather M0 with wifi, because I have a use for both units and (maybe one or two more further down the line), and I have the exact same symptoms with both displays.

So I have two feathers, two sets of wires, and two displays, and all 8 combination have the same behavior, with I2C working fine with 5V unplugged, but only the dots glow and only dimly, while with all wires plugged the I2C communication doesn't work.

I also tried hot-plugging and hot-unplugging the 5V wire, hopefully that doesn't do much harm, and I2C communication is broken when the wire is plugged and comes back when it is unplugged. Also when initializing the display with the wire unplugged and then plugging the wire, the display goes bright and the digits display whatever was send to the backpack earlier. So it's really as if the 5V connection somehow shorted the I2C communication.

Is it possible that the atwinc1500 wifi module somehow interferes with the 5V or the I2C of the backpack? Or is there some other feature of that particular board which can explain the issue?

The whole point of the project is to have a NTP-capable clock, so if there is a compatibility issue between the atwinc1500 wifi and the backpack I'd like to find out how to work around it. I expected the SPI bus and the I2C bus to be independent but maybe I'm wrong?

faelys
 
Posts: 12
Joined: Mon Sep 13, 2021 1:45 pm

Re: LED backpack issue with feathers

by faelys on Fri Oct 08, 2021 11:41 am

Another data point is that I managed to plug together a DS3231 breakout and the backpack on the same feather M0, I can see and communicate with both of them when the 5V wire is unplugged, and when the 5V wire is plugged the backpack becomes unresponsive without affecting the communications with the DS3231 (I haven't tried to actually use the DS3231 yet, but it does increment is register 0 about every second, so I assume things work correctly from one end to the other).

faelys
 
Posts: 12
Joined: Mon Sep 13, 2021 1:45 pm

Please be positive and constructive with your questions and comments.