Lately, I've been playing with a number of interesting and inexpensive I2C modules purchased online. Almost all of them have pads to mount a 2.54mm header – but I wanted an easier way to connect them to the QWIIC socket on my BEAPER Nano and BEAPER Pico circuits.

Unfortunately, not all of the header pin layouts on these circuits are the same. Most of the circuits I have on hand have one of two, common, pin-outs. I designed Adapt-2-QWIIC to adapt both of these two styles to QWIIC connectors.

Photo: Two different VL53L0X ToF (Time-of-Flight) distance sensor modules. Left are the front (top) and back (bottom) of one style of module, at the right is a second style of module. The second module has its VIN and GND pins at the opposite side of the header, compared with the first module, when both are viewed from the front.

What's QWIIC?

QWIIC is a 4-pin polarized connector ecosystem developed by Sparkfun to connect 3.3V I2C peripheral devices to microcontroller boards. It's one of a number of different interconnection systems, and this page on the Adafruit website has a good comparison of the most common interconnects.

The main features of QWIIC are: the use of a 1mm-pitch, 4-pin JST-SH connector and cable, and 3.3V operation for both power and I2C signals. Since I2C is a shared bus, QWIIC devices often include two connectors, to enable devices to be connected in a daisy-chain from one to the next.

Adapt-2-QWIIC

Photo: Screen shot of the Adapt-2-QWIIC layout in KiCad showing the pin header connections (bottom) and cuttable jumpers beside the R1 and R2 SCL and SDA pull-up resistors. At the top is a power LED and current-limiting resistor. The JST SH QWIIC connectors are on the back side.

In its simplest form, Adapt-2-QWIIC connects one or two JST SH QWIIC connectors to 2.54mm header pins.

Most I2C hosts and many I2C peripherals already include the appropriate I2C bus SCL and SDA pull-up resistors. Adapt-2-QWIIC provides two sets of 0805 SMD pads to let you add pull-up resistors if none of the other I2C bus devices contain their own. If, after mounting pull-up resistors on Adapt-2-QWIIC you find they're no longer needed, two cuttable jumpers lets you quickly disable them without any desoldering.

In the remaining bit of space left on the board, I also added pads for an 0805 LED as a power indicator and its current-limiting resistor – an unnecessary but nice-to-have addition to verify a device is (or should be) powered.

Building Adapt-2-QWIIC

While soldering SMD components is challenging, the use of 0805 components means it's easily manually accomplished with a fine-tipped soldering iron. For the JST-SH connectors, I find using a solder paste stencil and hot air or a hot plate for soldering easier – even if it takes a bit more time than manually soldering the pins. Since the main purpose of Adapt-2-QWIIC is providing QWIIC connectors, solder these onto the PCB first. Adding these first makes it easier to keep the board flat on a hot plate before adding the other components on the opposite side.

If your device needs pull-up resistors, add these next. 4.7kΩ is the usual common I2C pull-up value, but some higher-speed I2C circuits benefit from lower values such as 2.2kΩ resistors instead. But, it's important to know how many other devices on the I2C bus also include pull-ups, and their values to determine the best value of pull-up resistors to use.

If you'd like to include a power indicator, add an 0805 LED and current-limiting resistor. I've specified a 1kΩ resistor to minimize LED current in the schematic, but you can reduce its value if you want the LED to be brighter.

For most applications, you'll likely add a 4-pin header or header socket either at one end or the other end of the 6 through-hole pads in the board. Choose the position that matches the signals on your I2C device. I use a header socket on Adapt-2-QWIIC and matching header pins on the device for easy interchangeability. For a permanent connection with a lower profile and a smaller gap between the circuit boards, solder header pins directly into each circuit.

You can find a complete list of parts for Adapt-2-QWIIC shared on DigiKey.

Adapt-2-QWIIC is a simple circuit, and I hope it can be a useful addition to your hobby circuits bin!