Matrix Portal M4 with I2C Neopixel 1x4 Keyboard

[ntynen]

Hello,

I recently completed a project which utilizes the Matrix Portal (64x32 RGB display with ATSAMD51J19 Cortex M4). Using the I2C connector, I implemented support in my code for a Neopixel 1x4 keyboard.

When assembling the portal and keyboard, I observed that if I used any STEMMA QT / Qwicc cable longer than 50mm I would see periodic crashes. After a crash and resetting the board I would get the message "No pull up found. Check your wiring". If I turned the unit off, unplugged and plugged the same cable back it, it would work for a period of time. Also, any movement in the cable would result in the crash.

I've reworked the project to use a side mounted keyboard and 50mm cable. And it has been stable. However, it would be nice to be able to use a longer cable length.

I tried the following cables:

JST SH 4-Pin cable - 200mm (part 4401)
JST SH 4-Pin cable - 50mm (part 4399)
STEMMA QT/Qwicc cables - 100mm, 200mm (alternate manufacturer)
Build-your-own STEMMA QT/Qwicc cables - precrimped, 100mm

I looked over the documentation, and asked in Discord, but I could find nothing that indicated why anything longer than 50mm in length would cause this instability.

I tried two different boards (ATSAMD51J19 Cortex M4) and two different Neopixel 1x4 keyboards and observed the same behavior.

Does anyone have an idea why this happens?

Thanks,
Nicole

[johnpark]

I'm not sure why that's behaving that way, but I'd be curious if an active terminator would improve the cable length options. https://www.adafruit.com/product/4756

[ntynen]

Thanks for this information! I've added one to my cart for the next shopping trip. :) After I run some tests I'll let you know how it goes.