Connecting Raspi and Ardiuno gpio pins?

[quote=276058:@Derk Jochems]Well for one, you might burn the Pi’s chips. Second the communication could give errors.
It’s better to have 3.3v - 3.3v or 5v - 5v both with common ground.[/quote]
Thanks, Derk. As I’ve written, yours and Jean-Yves’ answer are conflicting. That’s the uncertainty that made me start this thread. Do you know for sure there is a risk or do you have any links to follow?

Currently, it doesn’t bother me that much because I reverted to USB communication, but it would be great to have a reliable answer. Any hints appreciated!

Sidenote: Like I wrote before, I tried it with a level shifter too and had no change in behavior except that the display that got its background lighting enabled via this level shifter came to life later. I suspect the level shifter itself, one of its lines seems to be somewhat slow.

I have burned a raspberry pi by doing so, the risk should be low but it’s always best to do it the right way.

The serial ports on my rpi b+ didn’t like the 5v of the arduino’s serial.

Trust me have done it alot of times, only 1 has stopped working but it’s a major pain to find the cause once you do so burn the chip.

Logic level converters are cheap, easy use and today mostly 2 way connectable.

Actually your problem is threading of the pi. The hardware pins have lower priority than the system but you leds ws2801 require all the comm time.

So it’s a timing problem yes. That could be causes by many things. Try stepping trough the suggestions.

You should atleast not use ws2801 on the RPI because it’s officially unsupported.

Did you actually use a library or code it yourself on arduino?

Thanks, Derk! As I wrote, I removed the interrupt Gpio connection which has fixed the timing problems.
One question: When you burned your Raspi, was it when you tried to talk back from the Arduino or did you use the pin connection to talk to the Arduino only?
I have an Arduino hat for Raspberry Pi here too which uses a direct pin connection. Only the pins are too short, so you cannot attach a breadboard connector. Makes me wonder if connecting both is really that dangerous.

Anyway: I was feeling uncertain about connecting both and I am glad the USB connection works.

I have the idea that pigpio could make using a WS2801 together with a Raspi possible. Currently I use FastLED on the Arduino which does a lot of color tricks that would take a lot of time to rebuild on a Raspi solution if it should work anyway. I have only run into an issue where the use of a palette returns wrong values which puzzles me at the moment.

http://www.newark.com/pdfs/techarticles/microchip/3_3vto5vAnalogTipsnTricksBrchr.pdf