Buy the Sense HAT – as seen in space*!

……

The board itself has a suite of sensors, a “D-pad” style 5-button joystick and an 8×8 RGB LED matrix driven by a combination of an LED driver chip and an Atmel AVR microcontroller – an ATTiny88.

For the terminally curious, here are the schematics of the board.

Here’s the hardware run-down:

Sensing elements:

Pressure / Temperature
ST Micro LPS25H
– 24-bit pressure measurement resolution (260hPa to 1260hPa)
– 16-bit temperature measurement resolution (0-125°C)
Datasheet

Humidity / Temperature
ST Micro HTS221
– 16-bit humidity measurement resolution (0-100% relative humidity)
– 16-bit temperature measurement resolution (0-60°C)
Datasheet

Acceleration/Gyroscope/Magnetic field
ST Micro LSM9DS1
– 9 degrees of freedom (X, Y, Z independent axes for all sensors)
– ±16 g acceleration measurement range
– ±16 gauss magnetometer measurement range
– ±2000 dps (degrees per second) gyroscope measurement range
Each of these measurement channels has 16 bits of resolution.
Datasheet

All of these sensors have features for periodic sampling of sensor values – complete with internal FIFO storage. The LPS25H and HTS221 have maximum sample rates of 25 per second, the LSM9DS1 has a maximum sample rate of 952Hz – we are already imagining the birth of a million Pi-controlled stunt quadcopters.

LED Matrix
The LED matrix is driven by a combination of a constant-current LED driver and an Atmel ATTiny88 running a custom firmware that delivers an 8×8 display with 15-bit resolution RGB colour. If you want to get into the gory details, the AVR firmware is available on Github.

Joystick
The Atmel is responsible for sampling the joystick. We didn’t have enough pins left on the Atmel to dedicate the five that we needed to sample the joystick axes independently, so they’ve been spliced into the LED matrix row selects. The joystick gets updated at approximately 80Hz, which is the scan rate of the LED matrix.

All of the sensors (and the base firmware for the Atmel) are accessible from the Pi over I2C. As a fun bonus mode, the SPI peripheral on the Atmel has been hooked up to the Pi’s SPI interface – you can reprogram your HAT in the field! We use this method to get the firmware into the Atmel during production test – and we leave it unprotected so you can substitute the stock firmware to get it to do whatever you want. Seriously. First person to turn this sensor HAT into a quadcopter controller HAT wins a cookie from me.

Software
If you’re not assembly-language inclined, you can always use the HAT’s sensors from our shipped Python library – standard function calls return sensor values, give you joystick key events and allow you to display things on the LED matrix. The Sense API is available through the Raspbian APT repositories.

To access the magic, simply enter:

sudo apt-get update
sudo apt-get install sense-hat
sudo pip-3.2 install pillow

into a terminal window. Note you will have to reboot for the Sense HAT to be recognised.

The API is well-documented (and tested extensively by schoolchildren as part of Astro-Pi) – get reading here.