Single Red Blink Followed By Normal Operation After Connection to Custom PCB

Hardware
1

Hi everyone,

I'm a bit stumped by this one. I have an M404 . When I plug it into the M.2 SOM Evaluation Board and power it via USB, the module turns on, the status RGB LED lights up white and starts flashing green, and it prints to the serial monitor. This sequence is as expected. When I then plug the M404 into my own custom carrier board, the RGB LED does not turn on and the module does not connect to my PC when a USB cable is connected. When I plug this M404 back into the M.2 SOM Evaluation Board and power is via USB, the RGB LED blinks red for a brief moment, turns white for a moment, and then starts flashing green like normal. When I unplug the USB cable (remove power) and plug it back in, there is no red blink, it just goes to white and then flashing green as normal.

The carrier board is a new revision of the design with very slight changes from a previous verison of the board. The difference between designs is just in moving some components slightly to adjust spacings between some conductors, but all connections and components are the same, and I've verified this through close examination of the board designs. The previous board revision worked perfectly with M404 modules running slightly different firmware. I've gone through the firmware carefully to check that the pin assignments and standard Particle setup functions are the same. I believe both are using Device OS 5.8.0. I've measured and confirmed that the carrier board is outputting the necessary voltages for powering the M404, and again, the power supply components are the same as the previous versoin which worked fine.

Finally, I have a B404 module running similar firmware (with different pin assignments). When I plug it into my custom carrier board and power it on, the RGB LED status light turns white and starts flashing green as expected.

Something seems to be happeneing to the M404 when plugged into my carrier board which casuses it to flash a red light the first time it is reconnected to the evaluation board. And whatever is happening doesn't seem to affect the B404.

I can't seem to find any helpful resources about this single red blink at the beginning followed by normal operation (no additional red blinks later on and no SOS).

Any ideas?

2

A single red blink is not built into the bootloader firmware. It's usually the result of a power issue, typically insufficient startup current or too slow of a ramp. It's actually a white blink, but because the red LED in the RGB LED typically has a lower forward voltage than green and blue, it looks red.

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