Scroll pHAT - which pins?

I’m about to order a Scroll pHAT to use with a Pi Zero, and I’m interested in knowing if there’s a way to use it while still being able to use some of the GPIO pins for other purposes.

So my first question is, which GPIO pins does the Scroll pHAT actually use? I’m pretty sure it must be only a small subset of them, but I don’t know which.

Assuming there are some unused pins, to my beginners’ eyes there are maybe two ways I could in practice access them.

  1. As far as I can tell from the picture of the header that is supplied with the Scroll pHAT, I won’t be able to access any of the GPIO pins for other purposes. So perhaps instead of using that header, I could instead solder wires to just the contacts on the pHAT that are needed, and plug them into the corresponding pins on a header that I solder on to the Pi Zero.

  2. If I do put a full header on the pHAT and plug it in like a normal HAT, maybe there’s some sort of special header that I can use on the Pi Zero and/or the pHAT that would enable me still to access pins? For instance, is there a way to have pins sticking out on both sides of the Zero so that I can plug a HAT in on one side and still access pins on the other?

Thanks in advance and be gentle - I’m a complete beginner with soldering, Python, etc etc!

I’ve made some progress in answering my first question, having now found which indicates that the Scroll pHAT uses pins 3 and 5 (presumably for I2C).

However, that doesn’t account for power. I don’t know on which pin it expects to draw (5V?) power, and where it expects to be connected to ground - can anyone help with that? While it seems that at the RPi side the 5V pins are identical and the ground pins are identical, it may be that at the Scroll pHAT side it is using connections to particular ones of these pins, and I don’t know which.

Plus I’m still keen to know whether my option 1 or option 2 (or some other option) is feasible for being able to access other pins!

For most add-ons power pins tend to be used on the left end side. It may not necessarily be always the case but it certainly is for the scroll pHAT. Here’s one of my ‘lazy’ soldering job to illustrate:

And here’s a link to a replacement header that will retain access to the GPIO:

Thanks so much for that - it certainly narrows down the pins I need to try.

That long-pinned header would presumably mean that I’d be accessing the spare pins on the LED-side of the Scroll pHAT. I’d rather leave that side clear to keep the display unobstructed and for possible fitting of a diffuser when it becomes available, so what I might do is just attach the standard header to both the Pi Zero and the pHAT, and test for (and then leave connected) the required pins by plugging in separate wires.

Well, you could use the tall-pin header on the Pi Zero and poke in jumper wires from the bottom side. There are other solutions such as using angled pins:

For power, since the question is asked often, the Scroll pHAT only requires 5V, which can be sourced from pin 2 or 4, or supplied externally to either of those.

For ground, I2c devices require a common ground for the entire bus. Pin 6 would be suitable and probably the most practical.

Mine’s running perfectly well using pins 3/4/5/6, leaving all the other GPIOs available for other tasks.