Micromod - 2 yellow blinks


Well-known member
Micromods are giving me 2 yellow blinks on my board. Several Micromods tested, all working perfectly fine in Sparkfun's Datalogging Board.

I'm making 5V from 12V, then making 3.3V (3.301V actual) for the Micromod. Giving 5V (Actual 4.82V) to VIN Pin 9, 3.3V on pins 2 & 74. Grounds on 1,7,33,36,39,45 & 75. All caps here are ceramic MLCC.

The other 5V inputs (VBUS & +5Vp) have all been tried and are normally not connected. I also jumped D3 and got 5.00V to VIN.

(Side quest - I placed a 0 ohm in R24, but that voltage never got above .8V and the 3.3V regulator didn't turn on.)

Prior rev of the board with different power, but identical GPIO connections works fine. Serial data & GPIO, all 3.3V logic. I2C is all NC at the moment.


I'm guessing it's power related.

This is the 5V and 3V3 rails when I set 12V power to the board. I think the dip at the 400uS mark might be the issue.


Do these spikes look like they could cause the 2 yellow blinks?

If I pull the MicroMod, this is the powerup. Ignore the noise and the channel swap, I was holding 2 probes on the board while connecting 12V power.


The 12V rail has lots of bulk capacitance.

My gut is telling me I need more capacitance on the 5V rail to prevent the droop. Maybe a tantalum?

All ideas and theories are welcome.

2 quick blinks means the bootloader can't see the main processor at all. Not good. I don't know why it's happening, but as a first troubleshooting step I'd take that MicroMod out and test it in a known-good carrier board. If it's been damaged or destroyed somehow, best to learn that sooner rather than later after wasting a lot of time and effort.

The blink code are shown at the end of the T4 bootloader chip page.

Thanks @Paul, the MicroMods all work fine when I move them to the SparkFun Board. I see the same behavior on several devices and several of my boards. And I swap MicroMods back and forth between sparkfun (boots fine) and my board (yellow blinks), so I don't think they are getting damaged.