HackSpace magazine

Adafruit CLUE review

By Ben Everard. Posted

This little board will look familiar to a lot of people. It’s based on the form factor of the micro:bit that’s been popular with schools in the UK and around the world, but comes with a lot more on board.

We can’t really skirt around the fact that this is an expensive microcontroller – it’s $39.95, not including delivery. However, for that, you get a whole lot of bits and pieces. It’s powered by an nRF52840 microcontroller which has a 64MHz ARM Cortex-M4 processor and 256kB RAM for crunching data, and Bluetooth Low Energy (BLE) for communication. On the front, the noticeable features are two buttons and a 240×240 pixel screen.

The display is small (just 1.3 inches), but a much higher resolution than we’re used to on maker boards. Of course, high-resolution can be a bit of a double-edged sword as it requires more processor power and RAM to be able to make use of it. Here again, the CLUE is well provisioned. This, combined with the recent speed improvements in the CircuitPython Displayio module, makes this display easy to use. It can also be used with the Arduino IDE.

Less noticeable is a whole bunch of other features. The full list is a little intimidating:

• STMicroelectronics series 9-DoF motion – LSM6DS33 accelerometer/gyroscope

• LIS3MDL magnetometer

• APDS-9960 Proximity, Light, RGB, and Gesture Sensor

• PDM microphone sound sensor

• SHT Humidity

• BMP280 temperature and barometric pressure/altitude

• RGB NeoPixel indicator LED

• 2MB internal flash storage for data logging, images, fonts, or CircuitPython code

• Speaker for playing tones and beeps

• Two bright white LEDs in front for illumination or colour sensing

It’s impossible to go through all of these in detail in a two-page review. We’ve gone through a few of the features in more detail in a tutorial on using CircuitPython on page 78. All the sensors are reliable, but maker level. For example, the microphone can record samples at 16000Hz, which is fine for a lot of uses, but don’t expect high-quality audio out of it.

Despite all the features, it’s a small board


There are good and bad things about the micro:bit form factor. It’s a good size for handheld devices (even for little hands), and the buttons either side of a central display are pleasing to use.

On the downside, we’re just not fans of the bottom connector on the micro:bit. It can be used with crocodile clips, but only three IO pins (plus 3 V and GND) can be accessed this way, and even then, only if you’re very careful to avoid touching any of the smaller pins. Banana plugs connect well to these holes, but not many other things connect to banana plugs. You can get banana-to-crocodile leads, which work great for the micro:bit, but only the micro:bit. If you’re planning on using a lot of external hardware with the CLUE, it’s worth considering a breakout adaptor such as Kitronik’s, which will make the IOs breadboard compatible.

The saving grace of the bottom connector is that it lets you push the micro:bit into expansion hardware and still access the buttons and display on the board. Note, though, that hardware designed for the micro:bit may or may not work with the CLUE. Software support is a particular problem as there’s no Scratch version for the CLUE’s microcontroller.

The CLUE extends the standard micro:bit form factor slightly by including a STEMMA QT connector which makes it easy to hook up I2C hardware. There are lots of expansions that are already compatible with this, including SparkFun’s Qwiic range and Grove’s I2C sensors (though the latter will require an adaptor). This, in our view, is a big advantage because not only is there a lot of hardware available off the shelf for this, but it’s easy to build your own.

You can power the CLUE via either USB or the battery connector

Lots of possibilities

That’s a lot of bits to play with, and that’s a good way of thinking about the board – a tool for learning about how to program a microcontroller with a lot of different hardware. There are probably few projects where it’s cost-effective to buy a CLUE rather than a more stripped-down board plus the bits you need. However, if you’re interested in learning about embedded computing – and particularly the programming side of it, then the CLUE is a great option because, while it might not be perfect for any one project, it’s great for lots and lots of projects.

We really like boards like this for learning and experimenting with. There’s so much bundled on the board that you can try out an immense amount without getting caught up in wiring. The inclusion of the STEMMA connection, in our view, is significant because this makes it much easier to hook up additional sensors and actuators.  

$39.95    adafruit.com

VERDICT Plenty to play (and learn) with in one small package.