I have a number of devices connected to Phat stack working just fine on 400 (keyboard model) but when move connector to bog standard Pi 4 it fails on i2C and thus Piicodev setup.
I move the same SD card between the systems so identical OS and config…
Running i2cdetect on the Pi400 gets me near instant display of everything live and good… do the same on the Pi4 and it takes over a minute and shows all as blank!
The green lights on the Piicodev devices show the power is live and ok on both setups so to me that means the orientation of the connector is ok for both… but one works and the other doesn’t!
I would have thought/hoped there’s no diff between a 400 and 4 as far as the underlying fundamentals but clearly something is amiss and different between them
The Pi4 is bog standard, unmodified, brand new etc so hoping it is all functional and ok so what could the difference be?
Frustratingly the Pi 4 is not showing boot screen now… it’s now impossible to continue checking on it.
The pins marked are ultimately access by the Piicodev Hat which itself is on the PHat stack as shown.
I’ve made everything work off that board (there is another HAT as well as individual GPIO for this project) so I can move them all from one system to another with just a single ribbon cable plug/unplug and not disturb anything else.
The same SD card with settings used on both systems… so the idea is just move the ribbon cable and the SD card over and power up and continue… or not
After the (new additional) Pi 4 fail I move the card and cable back to the 400 and all runs fine… very frustrating as I was expecting the move over to the Pi 4 to be trivial as the same chipset etc… just a different form factor.
I also have a Pi 5 experimenting with the new touch screen and AI Camera on the side but that breaks the WS2811 LED library I was using and GPIO so I can’t currently run my project on it as-is so it’s been hard work to get all the parts I want working in the same place at the same time… but the most surprising was the failure in moving 400 → 4
Ultimately I need the form factor of the 4/5 for packaging reasons and while the software development can continue on the 400 just fine I need to see it running elsewhere before too much longer…
I didn’t try the Piicodev modules directly as I wanted them to be on the Phat stack so I could move easily between test platforms… it was here that I hit the unexpected snag and was careful with ribbon cable placement and alignment
On the Phat I have a Piicodev adapter (drives Laser, OLED, buzzer, 3 x servo) and an Adafruit stepper motor bonnet… 3rd set of pins used for individual GPIO (LED strips, mechanical switch)
Now the 4 has given up the boot ghost and can’t even debug/test I2C issues further as it shows the initial rainbow screen then a black hole and never comes back… I’ve barely used it… and nothing even connected this time as just trying it bare bones… it’s a deeply frustrating experience at times
So it’s back to the 400 I have to go to at least keep developing code while I ponder the hardware and if I suddenly have a dead 4 or not with barely any use. (always careful with poweroff, unplug power before plug/unplug such as the Phat)
Plugging the Phat into the 400 and using same SD card all works a treat… sigh
It’s a shame what happened to the Pi 4, does its ACT LED blink when it is powered? This is often the biggest indicator of what a Pi error is. Fortunately you still have your Pi 400 to keep your project moving in the meantime.
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