Using an Arduino UNO, a Waveshare 128x128 1.5" OLED and an Adafruit BN055 gyroscope we create a simple artificial horizon and directional indicator that works upright and inverted. Not for use in flight... for educational purposes only.
The code draws a horizon consisting of a horizontal line and two orthogonal lines to give perspective. It then draws a little fixed aircraft diagram similar to what is actually used in many real devices consisting of 4 lines like this: ---V---. The horizon lines pitch and roll according to input from the gyroscope which is averaged for 20ms or so. To make life simpler I use a normalized -1--+1 display area and draw lines in that co-ordinate system and rotate them there too. Then they are mapped onto a 128x64 bit map which is then uploaded to the 128x128x4 bit map in the waveshare by doubling the rows and mapping every single pixel to either full white or off. This is necessary because the Arduino UNO does not have sufficient memory to store the entire image. On a higher performance processor you could do all kinds of cool stuff like draw brown vs blue skye etc.
In addition to the horizon and small plane it also outputs a gyro computed heading. When the device first comes up it looks the maximum magnetic flux and uses that to be the north reference, it then adjusts what the gyro tell it is the current yaw and computes what that would be relative to where it thinks north is. During the period that it is trying to figure out north it puts and X over the heading. Likewise if the gyroscope is not reporting that it is calibrating or calibrated we draw a big X through the entire display.
There is a brief youtube description of this project here: https://youtu.be/mU1mT4dsyRU
There is also a youtube description of the watchdog funtion here: https://youtu.be/h2vJ4zZMkqA