Alternate I2C bus on Raspberry 4B+

Nicolas BOYARD

Hello,

I have a Raspberry Pi 4B+ and a Duet 6HC. I want to connect them together and, now, I use the ribbon which connect The GPIO of the Raspberry to the GPIO of the DUET 6HC.
However, I need to shut down and (re)start the Rapsberry using au power button/switch.
Regarding to the data on the Rapsberry, it seems that only the GPIO 3 of the Raspberry is able to do that. But this GPIO 3 is also used by the ribbon of the DUET 6HC.

So, my questions are :

Is there an other way to connect the DUET 6HC and the Raspberry Pi 4B+ without loosing any functionnality?
If i will loose some functionnality, which are they?
If it is necessary to use the ribbon, what is the exact use of GPIO 3 on the Raspberry 4B+?
If the GPIO 2 & 3 on the Raspberry 4B+ are used for I2C communication, may I used the GPIO 0 & 1 on the Raspberry 4B+ which can also provide an I2C communication?

Best regards,

Nicolas

chrishamm

@nicolas-boyard Perhaps you're looking for something like this: https://www.ebay.com/itm/GPIO-1-to-3-Port-Extension-Board-Shield-Adapter-for-Raspberry-Pi-2-Model-B/164126432041?epid=25016259789&hash=item2636b29b29:g:Z8IAAOSwz09aoicT I use a similar shield to get access to the pins needed for the official RaspPi 7' display.

DIY-O-Sphere

@nicolas-boyard

You can switch the shutdown pin to another free gpio.
edit /boot/config.txt on the pi
You should find a line

dtoverlay=gpio-shutdown

change that to

dtoverlay=gpio-shutdown,gpio_pin=#

where # is the free gpio pin number
But I haven't found information witch is a free gpio pin on the ribbon cable

Nicolas BOYARD

Hello Chrishamm,

Thanks for your answer, but on the website of Duet (https://duet3d.dozuki.com/Wiki/SBC_Setup_for_Duet_3), it is said that :

"Duet 3 and SBC not communicating :

Use of Pi cases that extend the GPIO pins or use the pins for external buttons or powering PWM fans will not work with the Duet."

That's why I didn't look in this way. But I see that you're a admin of the forum, so maybe you have more information for this use case. To your point of view, could it work with tour solution?

More, I just saw that, according to the pin mapping of the SPI bus, the GPIO 3 of the Raspberry Pi seems to be unused by the DUET 6HC. I am correct? could i "cut the wire" and use it for a power button on the Raspberry Pi? (see : https://duet3d.dozuki.com/Wiki/Duet_3_Mainboard_6HC_Wiring_Diagram)

Hello DIY-O-Sphere,

I agree that the shutdown could be set on every GPIO (according to Raspberry datasheet), however, I also need to restart the Raspberry after the shutdown, by a button, and not by unpluging/pluging the power (My Raspberry Pi will be set in a closed box, after electrical transformer, so no access for no one in this box).

Best regards,

Nicolas

Nicolas BOYARD

Hello,

It seems to be solved. I just tried to connect each pin of the duet marked "used" (with dupont connectors), according to the wiring scheme , to my Raspeberry and they communicate. So I freed the GPIO 3.

Thank you,

Nicolas