Found a little more time to troubleshoot this with the actual hardware today as well as squint at the datasheets again.

I was at least able to determine a couple more things:

I believe I've finally understood the schematics well enough to confirm that the M5 PPS operates on 3V3 I2C. I had previously gotten mixed up while trying to sort out M5's various conventions for labeling the different I2C lines (e.g. prefixes like SYS/ISO/INT/PA) as well as the fact that the M5 PPS schematic is split across two pages and I hadn't understood the precise relationship there.

TL;DR: The pins I'm using are the ISO_SCL/ISO_SCL pins as shown in the schematic below, and they are tied to the VDDB pin on the U1 isolator component, which in turn is powered via ISO_3V3 from the header.

M5 PPS I2C Pullups to 3V3 on ISO plane.png

(I also finally understand the "ISO" prefix as meaning "isolated plane", which, OK, I'll admit to a little facepalm that this wasn't obvious to me earlier.)

My wiring to the STM32 Nucleo ties ISO_SCL/ISO_SDA directly to corresponding pins on the Nucleo, while sourcing ISO_3V3 from the STM32's IOREF pin (and FWIW, I've also tried the STM32's dedicated 3V3 pin as well as probed those pins to confirm 3.3V that looks stable).

Just because it was easy to test, I tried adjusting the I2C speed parameter wayyyyy down to the comically-slow 1 kHz -- with no apparent change in behavior... but then the moment I wrote that, I realized I should check whether the Adruino TwoWire implementation I'm using actually supports arbitrary speed. Sure enough, it coerces ALL speed parameter values to one of the de facto standard values of [100 kHz, 400 kHz, 1 Mhz]. So... apparently I proved nothing via that test and doing otherwise would require hacks I'd rather not get into unless that's a pretty strong hypothesis. Sigh.

Solved it, just had to scan this QR Code
https://community.m5stack.com/assets/uploads/files/1742537195503-bad5272e-aaac-47df-857b-c6d130524d36-image.png

IMG_8101.jpg

Yes - that is the resistor. Once I lifted the one leg (after removing the solder) the 120 OHM resistance was not measured across Can Hi and Can Low. I sure wish they had put in a jumper.

Hey Dennis, sounds like you’ve covered most of the basics. A few things to check: make sure the antenna switch (INT/EXT) is physically set correctly on the module. Also, the NEO-M8N can take a few minutes for a cold start—try leaving it powered outside for 15–20 minutes. Lastly, ensure it has a clean 3.3V power source; voltage drops can affect satellite acquisition. If none of that helps, try updating the GPS firmware via u-center. Two dead modules is unlikely, but not impossible. Good luck!

@kuriko
thank you.

Thank you everyone for all the messagges.

update>
I got it to work.
Spent many whours trying and playing with DIP, and was able to get it working bu using a FTL-UART board and connecting straight to U-blox, which was challenging since I dont have a windows pc and had to borrow one.

the main problem seems to be confusion with DIP, and cables.

thank you all for the help!!!!

I might "recover" this problem, althought I don't know why.
Only in japaness web page, you can find firmware of old version (But Its gone now....). When flesh back to old version , seems could solve this problem.here

There isn’t an official Eagle or DXF file publicly available for the ATOMIC Proto Kit layout. However, you might find community-made resources or footprints in forums or GitHub repositories related to ATOMIC boards. Alternatively, you could create your own PCB layout by measuring the board dimensions and pin headers manually.

@Kabron The benefit is that it can be used as an offline programmer. Love this idea in that I don't need to use a computer to program a few various HEX/BIN files to several different chips.

Once the partition.cvs table is converted for Arduino IDE, it made it simple to change the fat image for updates.

The project is set to be compiled with Expressif-IDF/IDE.
Modify the html / display code prior to fit your needs (Like updating to English to avoid confusion if you're trying to use the in program ability to upload files).

Same issue here, with the M5Stack Core 1. Just installed all the packages / libraries following the M5Stack instructions.

#include <M5Stack.h> void setup() { // put your setup code here, to run once: M5.begin(); M5.lcd.print("Hello World!"); } void loop() { // put your main code here, to run repeatedly: }

Output:

c:\Arduino\libraries\M5Stack\src\utility\pngle.c:31:10: fatal error: rom/miniz.h: No such file or directory 31 | #include <rom/miniz.h> | ^~~~~~~~~~~~~ compilation terminated. exit status 1 Compilation error: exit status 1

@twigs said in Using M5Stack for Custom Signage Displays – Need Advice:

Hey everyone, I’ve been exploring M5Stack modules for a custom signage controller project—curious if anyone here has experience using UIFlow or MicroPython for real-time display updates?"
"Also open to suggestions on the best units for LED or TFT screen integrations—appreciate any tips!

For a start, Micropython is not a realtime language, it is an interpreted language.

The biggest issue for signage is that of memory and ram, the bigger the sign, the more the memory is required.

screen capture M5core Webserial.png

@Anasilviaavalos had the same, M5burner bind with account and re-load firmware/ user application sorted it