Automation pHAT issues (breaking other HATs)

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1

Hi,

I have an automation pHAT, connectedit to a Pi Zero W using the mini Black Hat hack3r, along with a piTFT.

All was fine for a couple of days, then powering it up one morning, the TFT gives out noise. Removing the Automation pHAT solves the problem.

I have checked the GPIOs and there are no clashes. So:
Automation : I2C + GPIO[5, 6, 12, 16, 20, 21, 37]
TFT : SPI + GPIO[7, 8, 18, 24, 25,]

Apart from breaking out the SPI to a pin header, what could cause the automation pHAT to confict with the TFT?

2

as seen here https://pinout.xyz/pinout/pitft_plus_35 the screen uses bcm18 for backlight control.

Unless you completely disable the on-board audio of the Pi, I would expect trouble… that said I don’t have one of these screens to test.

3

which I have just realised does not answer your question - but AFAICT, no, Automation HAT shouldn’t screw things up, unless the pinout documented is incomplete or the noise is due electrical interference of some sort.

4

Thanks for the response. As I first stated, I checked there were no clashes before I purchased both.

It also, worked correctly for a couple of days and then made the screen go funky. So, I assume there is some undocumented features that cause issues after a while. But since I dont’s have circuit diagrams for both, I can not check…

5

How have you connected the 2 add-ons? … the TFT requires the HAT EEPROM i2c lines to be connected (phys pin 27-28). As per HAT specs, this means that Automation HAT should on the other hand not be connected to these lines, or the TFT auto-configuration will not happen correctly at boot time.

6

As stated in my first post, I am using the mini Black Hat hack3r. I believed, as it was I2C, they would be fine, afterall, that IS what the Black hat is for, is it not!

If that is not the case, how DO people connect multiple hats/shields?

7

again, you MUST disconnect phys 27-28 for one of the HAT, it will simply not work otherwise if one of them is relying on auto-configuration on boot (see the ‘EEPROM’ description on the TFT at https://pinout.xyz/pinout/pitft_plus_35).

One way to do that would be to snip those on one of the header on the mini Black HAT. Alternatively, use a full set of wires to connect exactly the needed connections for one of the HAT.

8

OK. Will give it a go.

Thanks