The beginnings of a new project. Software is coming together, but now it's time to pull together the hardware. This will be an antenna azimuth/elevation satellite tracker. In previous posts I have explored the calculations necessary and the details of using hobby servos to create a simple proof of concept.
For now I am experimenting with the ATMega2560 board (on the left) as it has plenty of flash and RAM space for the task at hand. I plan to control the device via a web page that it serves up, so for now I have an ethernet shield attached, though in the end the plan is to use WiFi.
Calculating satellite passes requires an accurate position for the observer in terms of latitude and longitude, but also elevation and time-of-day. I am using a GPS module to provide this information (lower right).
While the mighty ATMega2560 is certainly capable of generating the necessary PWM signals to position servos, I have decided to offload that to separate controller based on the PCA9685 which provides I2C interfacing of 16 channels of 12 bit PWM data. This particular board was originally intended to be used as an RGB LED controller, but my plan is to re-purpose it for this task. It has its own internal 25 MHz oscillator that offloads the ATMega2560 from having to generate these signals. That, plus the fact that I happened to have one on hand drove the decision to use this component to drive my servos.
After spending some time in the Avionics industry and working on electronic aviation attitude indicators, the math involved in Euler angle solutions to the orientation of a rigid body, plus the mapping of raw gyro, accelerometer and magnetometer sensor data into 3D space is a bit tedious. Fortunately for me, Bosch has done an amazing job of taking MEMS data from on-die sensors and adding an ARM Cortex M0 processor to produce a single chip solution that abstracts away all the raw sensor fusion and spits out data directly in quaternions, Euler angles or vectors.
The plan is to use this sensor mounted on the antenna fixture to measure azimuth and elevation relative to the calculated position on earth with no careful alignment of antenna orientation required. The Arduino will accept keplerian elements for the desired satellite and then automagically track the spacecraft as it passes overhead.
More updates as this comes together into a demonstrable solution.