hi,
I do not want that the BrickPi3 powers the Pi via battery / switch through the 5V GPIO pins, I just want to power my Pi via the USB cable. So how to cut or disable the voltage supply from BrickPi3 to the PI?
Why do you want to disconnect the BrickPi3 5v from the RPi 5v? You can use USB power at the same time as BrickPi3 5v power (batteries and USB).
If you want to power a stationary robot, you can connect a regulated power supply to the battery barrel jack connector. Make sure it’s suitable for the motors with load. Something like 9-12v 2-4A would be good for most applications.
If you need to disconnect the 5v lines for some reason, there are several ways you could do it (none of which are recommended).
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You could cut pin 2 on the RPi header so it doesn’t mate with the BrickPi3 female connector. Instead of cutting you could use a soldering iron to remove that pin.
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You could use a 2x13 ribbon cable to connect from the RPi GPIO header to the top of the BrickPi3 GPIO header, and then cut the 5v supply wire.
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You could modify the BrickPi3 circuit. You could take a knife to the traces on the BrickPi3, or you could unsolder one or more components to disable the 5v regulator circuit.
hello,
the reason is 1st, that I do not want the Pi to start if the battery is connected to the BP3 and switched on, I want to control the booting by another circuit via USB. 2nd, I want to be sure that an incidental over-voltage on the BP3 5V pin might not perhaps demage my Pi.
To cut pin 2 on the RPi header probably would be the simplest way then, thank you!
ooops, i missed that point - to cut the Pi GPIO pin is no option, because I do not want to destroy my Pi, and the RP3 pin cannot be cut because it’s female.
To unsolder things on Pi or BP3 is also no option, neither to cut traces with a knife, I am too much concerned to destroy anything incidentally. So unfortunately it’s still unresolved how to achieve the disconnection… 
You could use something like this between the RPi and BP3, and cut pin 2 (it will add about 18mm in height between the RPi and BP3).
You could use a ribbon cable like this and cut the wire that connects pin 2. The BP3 won’t be able to stack on the RPi.
If you want to be able to control the power electronically, you could add a relay or transistor between the battery pack and the BP3, and always leave the BP3 power switch in the ‘ON’ position. You could even use USB 5v to control the relay/transistor.
Why do you think the BP3 5v rail voltage will perhaps go high enough to damage the RPi? I’ve never had that happen, and I don’t remember having heard of such an issue.
well, my current Pi was destroyed during my last Robot control, but I have no idea what actually caused that issue. I am using 10*1.2V LiH battery cells, and when fresh charged they may have some over-voltage of almost 14V which might have caused an overvoltage also on the 5V DC/DC regulator, but that’s just a rough idea, nothing evident. Anyway, I think that an electrical seperation of Pi and BP3 circuit would be a good idea though.
The additional stacking header in between would make the stacking tower too high, I was hoping that there was something like a soldering bridge underneath the shield, or perhaps an obscured jumper, or perhaps even a software command to disable the 5V/5V connection. A ribbon cable might be an option though, in case I could make some space free in my robot chassis to mount the 2nd shield tower then.
Hi @HaWe,
Or you could have another set of 2x13 female headers stacked on top of your Raspberry Pi.
On that stack of female headers, I’d cut the power pin. This means you would be stacking the BrickPi3 board on top of 2 female headers.
This should help you save some space instead of using a ribbon cable.
Thank you!
yes, thanks, but that would also enlarge the over-all heigth of the multiple stacked shields-tower, like Matt already suggested, IIUC. To cut a Pin on the BP3 by tongs or unsolder a solder-bridge or unplug a jumper on the BP3 would be an option actually, but not acting with a knife and cut traces in the board, that’s too dangerous IMO.
Not to forget that i have multiple BP3 shields to be stacked upon each other.
Perhaps for a BP4 that design could be improved, additionally to 4 standard holes for mounting shields like in original HAT-designs, plus providing a 40-pin stack-through (B+, 2B, 3) GPIO header. 