Connectors

We use an abundance of components for temporarily or permanently creating electrical circuits. This page includes notes on some specific components we use in the lab, and is by no means comprehensive.

Modular Microcontroller Systems

Several manufacturers have sought to create modular part systems for easy connection of microcontrollers to breakout boards. As is often the case, they are similar but not compatible. (See https://xkcd.com/927/ for a commentary on this process.)

Grove System

The Grove System from Seeed Studio uses a four-pin latching connector. It supports multiple signal types, including I2C, Analog I/O, digital GPIO, and PWM. The pin functionality is not fixed and the user must take care to observe part compatibility, as can be seen below in the example pinouts.

The cables use female connectors to mate with male board headers. The pin spacing is 2 mm. The cables are not directional, both ends have the same wire order. The connectors are keyed for orientation and include a locking tab. The actual connector might be a proprietary NS-Tech 1125S-4P A2005 (not verified). Cables are available in different standard lengths. We do not have pins, housing, or a crimper which can assemble custom cables.

The typical I2C usage is as follow:

Pin	Color	Signal
1	Black	Ground
2	Red	VCC, 3.3V or 5V
3	White	SDA, I2C Data
4	Yellow	SCL, I2C Clock

Sensors with analog outputs appear to use:

Pin	Color	Signal
1	Black	Ground
2	Red	VCC, 3.3V or 5V
3	White	NC (no connect)
4	Yellow	OUT, analog sensor output

Servos with PWM inputs appear to use:

Pin	Color	Signal
1	Black	Ground
2	Red	5V motor power
3	White	NC (no connect)
4	Yellow	PWM, servo command input

The Cytron MD13S motor driver uses a Grove connector pinout:

Pin	Color	Signal
1	Black	Ground
2	Red	NC (no power to driver)
3	White	PWM driver input
4	Yellow	DIR driver input

The Maker Pi Pico baseboard includes six Grove connectors:

Pin	Color	Signal
1	Black	Ground
2	Red	3.3V
3	White	GPIO (variable function)
4	Yellow	GPIO (variable function)

Qwiic

The Qwiic connect system from SparkFun uses small four-pin JST connectors to carry I2C between modules. The connectors are polarized but not locking. Most components have two connectors to enable daisy-chaining the I2C bus from module to module. It is also possible (within reason) to fork the bus using small hubs. The Quiic connectors use a 1 mm pin spacing so are smaller than Grove. Cables are available in different standard lengths. We do not have pins, housing, or a crimper which can assemble custom cables.

This system has standarized on 3.3V I2C digital bidirectional communication. This reduces the chance of wiring incompatibility, although please note I2C devices need distinct addresses and may not be compatible together. Qwiic devices should not be attached to STEMMA QT using 5V, only 3.3V.

The typical I2C usage is as follow:

Pin	Color	Signal
1	Black	Ground
2	Red	VCC, 3.3V
3	Blue	SDA, I2C Data
4	Yellow	SCL, I2C Clock

STEMMA QT

The STEMMA QT connect system from Adafruit uses four-pin JST connectors to carry I2C between modules. There are two STEMMA connector sizes in use, a JST PH at 2.0 mm pitch and a JST SH at 1.0 mm pitch. The QT products use the smaller SH connectors and are compatible with Qwiic.

The electrical difference is that STEMMA QT allow for 5V operation, not just 3.3V. STEMMA QT products are required to accept 5V. Users of 5V microcontrollers should check voltage compatibility if mixing product families.

STEMMA

The STEMMA connect system from Adafruit includes analog, digital, and I2C interfaces using 3 and 4 pin JST connectors.

The larger 2 mm pitch STEMMA PH connectors follow a different wiring convention than the smaller QT SH connectors, instead they are similar to Grove. E.g, the I2C pinout is reversed:

Pin	Color	Signal
1	Green	SCL
2	White	SDA
3	Red	V+
4	Black	GND

It appears that 4-pin STEMMA connectors (2 mm pitch) can connect to Grove board connectors, although they lack the latch.

goBILDA Encoders

The goBILDA servomotors use a four-pin JST XH connector (2.5 mm pitch) for the encoder output using the following pinout:

Pin	Color	Signal
1	White	B phase output
2	Blue	A phase output
3	Black	GND
4	Red	VCC, 3.3 to 5V

goBUILDA offers a cable to connect this to a 4-pin JST PH compatible with 2 mm STEMMA (regular, not QT):

Pin	Color	Signal
1	Blue	A phase output
2	White	B phase output
3	Red	V+
4	Black	GND