Automation Hat Mapping


Can anyone find some time to help a learner with some questions about the Automation HAT layout?

I think I have mapped out most of the RPi pins to the Automation HAT layout from the PinOut GPIO diagram (, but I am left with a number of questions that don’t seem to be answered here ( If there is another reference source anywhere I couldn’t find it…

  1. I am trying to locate the BCM 2 (SDA) GPIO Pin 3 & BCM 3 (SCL) and GPIO Pin 5 to attach an LCD 1202 12x2. They are pictured on the PinOut diagram but I can’t see them on the HAT.

  2. I don’t understand the breakout header

a) #1 on left side (3V3)
Is this just another 3.3v source - in which case which GPIO pin does it map to?

b) #2 on left side (#25)
Is this GPIO pin 25 which according to my reference is another GND?

c) #3 on left side (ADC4)
Is this the Input mentioned in the Analog Usage info (“Three of the four analog inputs on Automation HAT are 24V tolerant, with a forth (!) 3.3V input in the breakout header”) - in which case which GPIO pin does it map to?

d) #4 on left side (GND)
Is this just another GND source - in which case which GPIO pin does it map to?

e) #1 on right side (MISO)
Presumably Master In Slave Out GPIO Pin 21?

f) #2 on right side (MOSI)

Presumably Master Out Slave In GPIO Pin 14?

g) #3 on right side (SCLK)
Presumably Serial CLock GPIO Pin 23?

h) #4 on right side (CE0)
Presumably Chip Select 0?

  1. BCM #2 and #3 are connected to the ADS1015 ADC internally, and are not broken out on the board itself. You could use a Black HAT Hack3r to access these. aims to document pins required for the board to function, and doesn’t include information about the breakout pins.

  1. For the most part it’s an SPI header, mapping to MISO/MOSI/SCLK and CE0 of the SPI0 bus:
    a) Due to its proximity, I’d guess it connects internally to physical pin 17, I’ll need to look at the schematic to be sure!
    b) That’s BCM 25, not physical pin 25. So it’s just a regular ol’ GPIO pin:
    c) ADC4 doesn’t map to a GPIO pin. It’s connected to the ADC which, in turn, is connected to the I2C bus.
    d) The ground plane in our boards is almost always continuous (IE: all the ground pins are electrically connected and don’t really map anywhere), so it doesn’t map to any specific pin. usually specifies which ground pins it’s a good ideas to connect, though.
    e) Correct MISO = Physical pin 21, or BCM9
    f) Nope MOSI = Physical pin 19 or BCM10
    g) Correct SCLK = Physical pin 23 or BCM11
    h) Correct, AKA BCM8 or Physical pin 24

Much of this is documented on the reverse of the HAT, too.

  1. BCM #2 and #3 connected to the ADS1015 ADC internally…Black HAT Hack3r …>>
    Is this the only option if my LCD unit is looking for SDA & SCL connections ?

  2. SPI header comments - Understood thanks


It’s far from the only option, but it’s probably the most straight forward.

You can, for example, solder wires to those GPIO pins on the bottom of the Pi. As long as you’re careful, the i2c bus wont mind being extended to another device or two, or more!


to add to this, it would be relatively trivial to grab those pins on the underside of the HAT, since it uses a surface mount header… what’s best depends on where you want your LCD to be (semi) permanently connected, the Pi or the HAT.


I have ordered the Black Hat anyway (I’m sure it will get used for this or something else), but I will investigate these options as well.

Thanks for the support