Can I use a HAT hacker HAT with these two

Support
1

Hi guys

I am thinking of purchasing one of these :

What I want to do is mount a Unicorn HAT Mini at the top :

And an Inky WHAT e-ink screen at the bottom:

The Hat Hacker has a handy drawing showing the sizes, but I cant quite figure out if things will fit. Because the screen and unicorn overlap the GPIO pins a little, its hard to get a read on if this will fit.
Anyone done something like this before?

Many thanks!

2

Before you worry about physical conflicts, you need to look for pin conflicts.
Unicorn HAT Mini at Raspberry Pi GPIO Pinout
Inky wHAT at Raspberry Pi GPIO Pinout

It looks like they both use SPI0. I donā€™t think you will be able to use both on one Pi?

3

Oh crap. You are right. They do have some of the same pins. I am new to all this, so Iā€™m not sure if they can be shared?
Or do they have different addresses? Iā€™m not sure what that means, but I remember people talking about that somewhere. šŸ˜¬

4

The shared SPI-bus is not the problem. The problem is that the Uncorn HAT Mini has two internal devices and the HAT uses both chip-select lines of the Pi named CE0 and CE1. The ā€œCEā€ stands for ā€œchip-enableā€ and is a synonym for chip-select. The Inky only uses CE0 so you could combine the Inky with a display that uses (only) CE1.

1 Like
5

@bablokb , Yeah, I saw that. I just got lazy in my reply and didnā€™t elaborate. My bad.

1 Like
6

So is there a way to switch between them perhaps? The inky screen could be updated every couple of hours, and then I could run the unicorn while the inky isnā€™t being updated?
Since the inky will just continue showing what was last updated anyway.

7

This is not how SPI works. All devices on the bus share the clock (SCK) and the data-line (host->device, traditionally called MOSI: master-out slave-in). A device knows that the data is for itself when the chip-select is pulled low.

So when you try to update the Inky, you would pull the CS low to tell the Inky that you are sending data. But the Unicorn will also have the shared CS low and will also think the data is for itself. And vice-versa.

8

Ok. Thinks for explaining! I really appreciate it!

9

I have Pi setups with dual and triple SPI LCD displays in use. Like @bablokb said, as long as each display uses a different chip select pin, its doable. One issue for you is The Unicorn Hat Mini uses CE0 and CE1. I think thatā€™s going to conflict with the use of CE0 by the Inky What? They are both using SPI0.