Pi zero hat compatibility

Question

I need help determining if these two devices are compatible on the raspberry pi zero w. I just got the adafruit pitft plus 2.8

https://www.adafruit.com/product/2298

Site says pins used are SCK MOSI MISO CE0 CE1 Gpio 25,24 It also uses gpio pins 23,22,21,18 for the buttons from what I read somewhere else. Idk if it's possible to change those pins but I can remove the buttons if I must. I would prefer not to though.

and I want to get the just boom amp zero phat

https://www.justboom.co/product/justboom-amp-zero-phat/

I can only find the pinout on pinoutxyz.com and idk if it's even right. I was hoping someone could try and help me figure out if these two devices are compatible together.

Thank you for your help.

Edit. I have googled this it's just that as far as I know the just boom amp zero phat is relatively new to the scene and this is also my first raspberry pi build. I've done much with Arduino since I'm in college for engineering and I've used a raspberry pi before but I've never actually compiled a list of components to build something on my own. Thank you again for the help.

Answer 1

As it says in bold print on the Adafruit page:

This updated design fits perfectly onto the Pi Zero, Pi 3, Pi 2 or Model A+, B+! (Any Pi with a 2x20 connector)

This is because all 40 pin models have the exact same pinout, just as all 26 pin models have the exact same pinout. So if you find a hat intended for the Pi that has a 40 pin plug, it is compatible with the Zero W, including the JustBoom amp which says on its product page:

designed specifically for the Raspberry Pi Zero and Pi Zero W

It's not clear in your question if what you mean is, "Can I use these hats at the same time?", to which the answer is, "maybe". The Adafruit product page makes it explicit that it uses the SPI bus (including both chip select pins, so that means no other device can use the bus) plus GPIOs 25 and 24.

The JustBoom pinout does not use SPI, it uses I2C, which the PiTFT does not. So the only obstacle are the overlapping GPIO pins. Not all GPIOs are created equal though -- here's a chart including the potential specializations of each pin, based on which I'd make the following observations:

• The PiTFT uses GPIO 18 (BCM numbering) for backlight control. This will certainly mean it is using it as a PWM pin. Although there are 4 PWM pins, there are only two clocks: GPIO 12 and 18 are on one, GPIO 13 and 19 on the other.

  The amp hat uses 18 for the PCM clock. There is not another option there, and it also uses 19 for PCM. This means you probably could use 12 or 13 for the TFT backlight instead.

• Both hats use 24 and 25. But these do not, I think, have any special purpose that is being exploited. So likely that could rearranged.

Of course this mean tweaking some source; almost certainly that for the Adafruit board is available. Likely both of them use a device tree layout which will need tweaking as well.

Neither hat is stackable though, so using them both at once is going to get a bit messy. Further, even if they were stackable, those pin correspondences are hardwired on the hat, so presuming the tweaks above work out, at least one of them cannot be put directly on the Pi's breakout.