A pH monitoring circuit is one of the simplest circuits to construct in reef-pi. Here is a general overview of the connections: Raspberry Pi's I2C pins (SDA and SCL) is connected to the EZO circuit, along with power (5V) and GND connection. You can find more details in official Atlas Scientific wiring guide
It is recommended to use two 4.7K pull up resistor for SDA and SCL connections. We'll use a Mint tin size Perma Proto board to create 5V and GND rails and to mount male/female headers where Pi, EZO and input power will be connected. Here is a Fritzing breadboard view of the entire setup
I am using yellow solid core wire to denote SDA pin and green solid core wire to denote SCL pin. Female header pins are soldered to mount the EZO board and BNC connector.
Ignore the red solid core wire at the bottom, it was soldered by mistake. Also, there are four female headers at the bottom to connect BNC connector, but only the three rightmost ones are used.
EZO board attached to the female headers
And the entire circuit, including BNC connector. Note: I am using just BNC connector here, but I recommend using the ones with carrier board for voltage isolation (linked in the parts list)
That's it, next we'll move on to fabricating the enclosure