This is a Raspberry Pi hat meant for use with CraftBeerPi. It's created with EasyEDA and optimized for production via JLCPCB.
This project is certified as open source hardware by the OSHWA under the UID DE000132.
Currently this project is designed with EasyEDA. You can find
all necessary files in the folder easyeda. When modifying this project please
respect the CERN-OHL-S license used in this project.
- Slots for up to 5 MAX31865 modules for PT100/PT1000 measurements
- 7 digital outputs with up to 1 amp of output power
- All 7 outputs have flyback diodes to drive inductive loads like solenoids
- All 7 outputs have resettable fuses for extra protection
- RTC so the Raspberry Pi doesn't loose its time in offline installations
- QWIIC connector to hookup additional sensors and actors following the SparkFun QWIIC specification
- OneWire connection for additional sensors
- Can operate on 12-24V, digital outputs operate directly on input voltage
- Reverse voltage protection (but please be still be careful)
Please note that the digital outputs are inverted in logic due to the push pull stage, but CraftBeerPi supports inverting GPIO actors.
This board is powered by 12-24V and provides some reverse polarity protection. But still please be careful when wiring up the board. Looking at the front of a connector the left side of a connector is always the negative side and the right side of a connector is always the positive side!
PCB:
Schematic:
Digital outputs are counted starting on the most left. Outputs 2,3 and 7 are marked on the edge of the PCBs upper layer. On the bottom layer every output is numbered and the polarity marked. On the upper layer polarity markings are only next to the outer most ports on each side. But polarity is always left side negative, right side positive.
| Output # | GPIO |
|---|---|
| 1 | 25 |
| 2 | 8 |
| 3 | 7 |
| 4 | 12 |
| 5 | 16 |
| 6 | 20 |
| 7 | 21 |
The MAX31865 modules are connected via SPI and each have a different CS-Pin. Modules 1,2,3,5 are mounted with the upper side facing left (towards the power connector and the SD-card slot of the Raspberry Pi). Module 5 is flipped 180°. Every module connector has the first two and last two pins marked with the same markings as the module to ensure the correct orientation.
| Modules # | GPIO CS |
|---|---|
| 1 | 17 |
| 2 | 27 |
| 3 | 22 |
| 4 | 5 |
| 5 | 6 |
The OneWire data line is connected to GPIO 4. The pins on the connector are marked behind the connector
on the top side of the PCB. They are, from left to right VCC - DAT - GND. A 4.7k pull up is
already provided on the board.
To enable OneWire support on a Raspberry Pi you need to add
dtoverlay=w1-gpio,gpiopin=4
to your config.txt
The RTC (DS3231) is connected via I2C and should be usable by adding
dtparam=i2c_arm=on
dtoverlay=i2c-rtc,ds3231
to your config.txt
- On revision 1.0 outputs 2 and 3 are mapped to chip enable pins of SPI0. Users need to disable CE pins on SPI0
- On revision 1.0 outputs are not in the desired off state during and directly after boot
To solve these issues the Raspberry Pi can be configured via config.txt.
With adding dtoverlay=spi0-0cs to the config.txt you can disable the hardware CE pins for SPI 0, freeing up GPIO 7 and 8
making Output 2 and 3 freely usabel.
With gpio=25,7,8,12,16,20,21=op,dh in the config.txt we set all pins controlling powered outputs to output and pull them high
as early as possible to disable the outputs. During power on there might be less than a second where the outputs might be enabled.
# Enable SPI
dtparam=spi=on
# Enable 1-Wire
dtoverlay=w1-gpio,gpiopin=4
# Enable RTC
dtparam=i2c_arm=on
dtoverlay=i2c-rtc,ds3231
# Disable SPI0 CE pins
dtoverlay=spi0-0cs
# Disable outputs on boot
gpio=25,7,8,12,16,20,21=op,dh