Pin Out – Cable Tester

I2C Pin Out (STEMMA from Adafruit)

STEMMA is a connector system designed to simplify connecting sensors and other devices to microcontrollers and single-board computers. Used by Adafruit, STEMMA aims to streamline the process of prototyping and building electronics projects.

Do take note that STEMMA is a different connector to STEMMA QT. The pin out is similar but the connector is much smaller for STEMMA QT, suitable for smaller sensor circuit board.

The I2C cable connector from STEMMA (Adafruit) is compatible to Grove (Seeed Studio). Their connector and the pin out are the same.

STEMMA I2C connector details

STEMMA I2C inter-connection system uses PH series from JST. JST specialises in connector product. The following is the datasheet and drawing for the JST PH series connectors use.

Datasheet, JST PH 2.0mm pitch connector (pdf 1.0MB)

Cable Plug

Housing part number: PHR-4
– Available from Digikey: 455-1164-ND

Crimp Pin part number: SPH-002T
– Available from Digikey: 455-1127

Board Socket

– Socket part number: B4B-PH-K-S (Available from Digikey: 455-1706-ND)
– Socket part number: S4B-PH-K-S (Available from Digikey: 455-1721-ND)

Tools Accessories

Tool hand crimper 28-30AWG side, part number WC-240 (Available from Digikey: 455-1128-ND)
TOOL EXTRACTION PH SERIES CONTAC, part number EJ-PH (Available from Digikey: 455-EJ-PH-ND)

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I2C Pin Out

I2C is a short name for Inter-Integrated Circuit. I2C is a simple two-wire serial protocol used to communicate between chips in an embedded system. I2C has two lines SCL and SDA, SCL is used for clock and SDA is used for data.

I2C is really not designed as a protocol over the cable. The convenience of I2C allows additional chip or circuit module to be added without affect the overall circuit design. This popularity and convenience of I2C lead to people using it as a protocol to communicate between 2 circuit modules over a cable. This cable is usually 4 wires. Two wires SDA and SCL for the data. Two wires VCC and GND for the power. VCC for I2C cable is usually either 5V or 3.3V.

Over the years, circuit modules producing companies starts to come up with their own name of their I2C ecosystem standard. They are still the same basic I2C 4 wires cable. However the type of connector used and the pin out varies. These leads to some variation of I2C cable system standard.

There is not yet an international standard of a I2C cabling system. The following presents the available I2C cable and pin out of varies brand on the market.

At this moment of writing, there is 5 types of I2C cable system that I have found, out of the seven I2C system brand name. Those with the same background color means that the cabling system is compatible and can be inter-swap with one another.

The recommended standard I2C cabling to implement, I would personally prefer to follow

Grove (Seeed Studio), STEMMA (Adafruit) for standard I2C cabling system.
qwIIC (Sparkfun), STEMMA QT (Adafruit) for mini-connector I2C cabling system.