1. Watchdog
Quick read about using a watchdog for a product that is difficult to reach, so it should reboot itself in case of a problem: https://hackaday.com/2021/10/14/basics-of-remote-cellular-access-watchdogs/
Jack Ganssle has been writing about embedded systems for a long time. Any time you see an article by him, you should take time to read it!
2. Timers and PWM
Pulse-Width Modulation
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Pulse width: … the width of the pulse (high time, usually). Measured in duty cycle (high / period), or high/low times.
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Modulation: varying a property of another signal
3. Servo: motor + position control
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Everyone gets an SG90 servo to keep.
TowerPro SG90 servo datasheet: https://drive.google.com/file/d/1IYrXqi3QZPs6FQUHoZGrPoCTo4iSEi4h/view?usp=sharing
The "fg90" datasheet has more technical information.
How does a servo work?
Glad you asked!