IO Expander Breakout

Can anyone tell me about the VIN+ and GND- connectors.
The VIN+ appears to be connected to 3-5V but the GND- is not connected to GND.
A circuit diagram of the board would be nice. Can anyone share?

If you have it plugged into a breakout garden hat, but that hat is not plugged into a Pi, some of the GPIO ground pins may not be linked together?
All the GPIO ground pins are common on the Pi itself, but that’s not always possible to do on a Hat or pHat. They will all be linked together when attached to a Pi though.
Just something to keep in mind.

Are you saying the 4 pins marked GND, aren’t connected to the GND pin on the edge connector? That would be very surprising (to me anyway) if true?

Yes, exactly that is indicated using a continuity meter. But connecting a potentiometer across VIN and one of the 4 pins marked GND gives a voltage on the slider when the expander has power.
Perhaps it’s to do with the reverse voltage protection provided by the board. There is a transistor close to the GND pins. Maybe it connects the two GND’s when power is applied.

This is all just curiosity on my part really. The board seems to work OK.
btw I’m not using a breakout garden.

Ok, weird? I have the Breakout Garden Mini SPI i2c, I don’t have that breakout though.

Thinking about it, I’m not sure why they would have marked it VIN if it was just 5V or 3.3V, because why not just say that?

It might be worth asking on Twitter or opening a Git issue, unfortunately the Pimoroni staff aren’t super active here. Unfortunately they don’t tend to publish schematics of their boards.

1 Like

I believe the board is capable of working between 3v and 5v, but I agree VIN is an odd designation. I’m not a Twitter person, and as you say, this is probably not a good forum for these questions.
Thanks to all who have chipped in.

Actually, the IO Expander is pretty well documented. On its product page you’ll find links to the board’s schematic as well as the Datasheet and Technical Reference for its Nuvoton MS51 microcontroller.

That’s a recent addition, but welcome.
Thanks for pointing it out.

You can power the expander with 3.3V or 5V. If you use the breakout garden HAT it will be 3.3V. If you e.g. want to run servo’s (PWM) you will need 5V and have to power it with that. VIN will be the same voltage as the one you use to power the module.

The boards 4 GND pins are NOT hard wired to the input GND. This would also probably be because of PWM issues or Pimoroni’s reverse polarity protection.