What is STEMMA?

You may have noticed that starting in 2018, a lot of Adafruit development boards have connectors that look like this:

We call these STEMMA connectors - technically they are called 3 and 4 pin JST PH connectors. They're our way of making it easy to plug-n-play various sensors and devices without a lot of wiring. Especially with the board isn't breadboard-friendly, as above.

The idea is that by having easy-to-plug cables, you can wire up things without soldering, wiring and complexity. For example, here's a STEMMA soil sensor.

Adafruit STEMMA Soil Sensor - I2C Capacitive Moisture Sensor

PRODUCT ID: 4026
Most low cost soil sensors are resistive style, where there's two prongs and the sensor measures the conductivity between the two. These work OK at first, but eventually...
$7.50
IN STOCK

As you can see, the soil sensor has a matching 4-pin JST PH connector on the end.

The sensor is well suited to using a cable connection - its an I2C sensor so needs 4 pins, and you will want to stick it into a plant, so it makes sense to have it on a cable!

Plugging in the sensor is easy, you just need to connect a JST-to-JST cable. So for example, you can make a IoT plant monitor with the two parts above with no soldering or special wiring.

STEMMA connector types

There are THREE different STEMMA connectors you will see:

  • STEMMA 4 Pin JST PH - These are larger 2.0mm pitch connectors
  • STEMMA 3 Pin JST PH

STEMMA 4 Pin JST PH - These are larger 2.0mm pitch connectors

They are for I2C use!

STEMMA 3 Pin JST PH - These are larger 2.0mm pitch connectors

They are for PWM/Analog/Digital use!

STEMMA QT ('cutie') 4 Pin JST SH - These are smaller 1.0mm pitch connectors

They are for I2C use when the larger JST PH connectors won't fit on a small sensor board!

This guide was first published on Jul 28, 2019. It was last updated on Jul 28, 2019. This page (What is STEMMA?) was last updated on Oct 22, 2019.