Great news! We have a sponsor! PCBWay will build our prototypes for free! Actually, the greatest challenge with our present board is the tiny size of the compass chips. They are sub mm and proved to be not hand solderable. So PCBWay is a real game changer here. With automatic machines they certainly wont have an issue.

With renewed motivation I transferred the firmware from the break out board assembly to the single circuit board. Achievement so far:

• Tested the motor controllers. They work like a charm.
• Transcribed RTC operation – tedious bit masking and I2C timing issues, but now it works.
• Connected external MPU9250 compass – because I don’t have the new chips yet.
• Ordered new magnetometer as a breakout for testing.
• Unconventional motor current measurement.

The last point was an open issue. We have an overvoltage surge protection diode to protect the FETs and we measure the spillover current. It works! Yet it will be dependent on the inductivity of the power supply and the cable. Actually current measurement can be quite energy consuming. Hall sensors draw something like 10-20 mA from our 24V supply and would heat up the voltage regulators. They also tend to be costly – not to mention chip shortage. The conventional method with shunts costs voltage and requires an additional op amp. So, I believe our solution is quite elegant.

The current measurement is important to detect blocked motors or damaged gears. If the current rises steeply, the motor is fully blocked and the tracker needs to stop. If the individual tracker reports higher and higher current consumption to the central field control, it is probably time for a service, e.g. lubrication. For both purposes a relative measurement is fine and we proved that our spillover method will do the trick!

So everything works as expected so far. We will wrap up the last necessary changes to the board and then we can have the final version built in a professionally by PCBWay.