In 2014, Adafruit designed development boards with standard connectors for interfacing external sensors and modules. As they are known, STEMMA is typically 3 and 4 pin JST PH connectors using PWM/analog/digital and I2C communication for the interfacing purpose, respectively. Sized at 2.0mm pitch connectors are seen to be larger for small and wearable hardware modules. In 2018, after the introduction of Qwiic, Adafruit came up with STEMMA QT, technically 4 pin JST SH, as a smaller 1.0mm pitch connector using I2C communication.
While designing standard connectors, most of the top embedded electronic manufacturers, including Adafruit, Seeed Studio, SparkFun and DFRobot, focussed on the cross-compatibility of the connectors with each other. Interestingly, Qwiic controllers are directly compatible with STEMMA QT modules without the need for an adapter, while Grove and Gravity controllers require a 4-pin cable adapter from JST PH to JST SH. They signify that the STEMMA QT connector is identical to the Qwiic connector and uses the exact pin ordering. The only difference is that Qwiic has level shifting and voltage regulation on the controller and not devices, so you can use Qwiic devices on a STEMMA controller if you set the voltage jumper from 5V to 3V.
One of the most famous Adafruit sensors with STEMMA QT JST SH connectors is the PCT2075 temperature sensor with integrated NXP’s PCT2075 temperature-to-digital converter with an accuracy of ±1°C operating over a range of ‑25°C to +100°C range. They are considered a drop-in replacement for the commonly used I2C temperature sensor, the LM75. Compared to LM75, the 11-bit ADC in the PCT2075 provides more precise measurements. Without the need for soldering, the PCT2075 temperature sensor can be interfaced with the host hardware platform through STEMMA QT connectors. Supplied with the temperature threshold feature, the user can set a high-temperature threshold that the sensor will compare to the current temperature and alert when the current temperature exceeds the threshold.
Specifications of Adafruit PCT2075 Temperature Sensor
- Type: Temperature Sensor
- Accuracy: ±1°C
- Operating temperature: ‑25°C to +100°C
- Dimensions: 25.5x18.0x4.6 mm
- ADC resolution: 11-bit
- Temperature resolution: 0.125°C
- Connectors: STEMMA QT JST SH connector
- Temperature threshold: 80°C
This ambient light sensor provides 16-bit light measurement in lux, a standard light measuring SI unit– making it easy to compare with references from other sensors. The BH170 light sensor can measure light from 0 to 65,000 lux, and with some calibration and adjustments, this can be increased to measure as much as 100,000 lux. Fabricated in a STEMMA QT form factor, the BH170 integrated a voltage regulator and level shifting circuitry on 3.3V devices like Feather M4 and Raspberry Pi and 5V devices like Arduino.
Specifications of Adafruit BH1750 Light Sensor
- Type: Ambient light sensor
- Light measurement resolution: 16-bit
- SI Unit: lux
- Measurement range: 0 to 65,000 lux with a limit of 100,000 lux
- Connector: STEMMA QT JST SH connector
- Compatibility: 3V3 and 5V host platforms, including Raspberry Pi and Arduino
- Dimensions: 25.3x17.7x4.5 mm
For environmental applications where you are required to check the water pressure with relative changes in pressure and absolute pressure. To help you with both demands, the Adafruit LPS33HW pressure sensor combines protection from water intrusion while maintaining high precision for relative and absolute measurement. STMicroelectronics’ LPS33HW is an ultra-compact piezoresistive pressure sensor that acts as a digital output barometer with an IC interface to communicate through I2C and SPI protocols. Providing 24-bit pressure data and 16-bit temperature data has an accuracy of +/- 0.1% hPa for pressure readings.
Specifications of Adafruit LPS33HW Water Resistant Pressure Sensor
- Type: Pressure sensor
- Integrated circuit: STMicroelectronics’ LPS33HW
- Communication protocol: SPI and I2C
- Operating range: -40 °C to +85°C
- Absolute pressure range: 260 to 1260 hPa
- Supply voltage: 1.7 to 3.6 V
- Pressure data output: 24-bit
- Temperature data output: 16-bit
- Dimensions: 25.7x17.7x4.6 mm
The combination of a triple-axis accelerometer and gyroscope on a single PCB makes it one of the most demanded sensors for various hobbyist projects. The integrated classic 3-axis accelerometer tells which direction is down towards the Earth while the gyroscope detects and measures angular motion. InvenSense’s MPU-6050 is a low-power motion tracking device that can access external magnetometers and other sensor data without intervention from the system processor.
Specifications of Adafruit MPU-6050 6-DoF Accel and Gyro Sensor
- Type: IMU sensor
- Sensors: 3-axis accelerometer and 3-axis gyroscope
- Integrated circuit: InvenSense MPU-6050
- Communication protocol: I2C
- Interfacing other sensors: Access external magnetometers or other sensors through an auxiliary master I2C bus
- Dimensions: 26.0x17.8x4.6 mm
- Weight: 1.8g
For altitude measurement, the Adafruit sensor comes with an integrated Infineon DPS310 high precision digital barometric air pressure sensor for measuring altitude change with high accuracy and low current consumption. The sensor is capable of measuring both pressure and temperature with an accuracy of +/- 0.002 hPa and +/- 0.5°C, respectively. The sensor data is available through the serial I2C and SPI interface.
Specifications of Adafruit DPS310 Altitude Sensor
- Type: Barometric Pressure / Altitude Sensor
- Operation range: Pressure: 300 to 1200 hPa and Temperature: -40 to 85°C
- Pressure sensor precision: +/- 0.002 hPa (or ±0.02 m)
- Relative accuracy: +/- 0.06 hPa (or ±0.5 m)
- Absolute accuracy: +/- 1 hPa (or ±8 m)
- Temperature accuracy: +/- 0.5°C
- Pressure temperature sensitivity: 0.5Pa/K
- Power supply: 1.7 to 3.6 V
- Average current consumption: 1.7 µA for pressure measurement and 1.5uA for temperature measurement
- Interface: I2C and SPI
- Dimensions: 25.5x17.7x4.6 mm
Final thoughts on STEMMA QT Sensors
For small development boards and wearable modules, STEMMA QT has served the purpose of a standard connector to interface external sensors. Following the same design as the Qwiic connector, STEMMA QT offers excellent cross-compatibility. Several more external sensors with STEMMA QT connector support are available in the market.
Your turn: Have you got any experience with STEMMA QT Sensors? Let us know which one is your favorite in the comments section below!