Start with the tutorial on Basic EE by Rebecca Bruce
The most basic output device is the LED, but don’t fry your LED.
- Sparkfun’s LED Current Limiting Resistors tutorial or Adafruit’s All about LEDs tutorial
- current limiting resitor calculator
- Some specs
Controlling power with LEDs and servo
Controlling power with PWM
Pulse Wave Modulation is the most common way to control the brightness of an LED. (Unfortunately, Raspberry Pi is behind Arduino in this one.)
Controlling motion with a servo
Servos are frequently used in low-power motors that require accurate positioning. Servos provide a way to separate motor and processor power.
The PCA9685 was built to control LEDs, but it can also be used with Servos and other PWM-controlled devices.
- Adafruit board for PCA9685
- Arduino with PCA9685 tutorial
- Raspberry Pi with PCA9685 with Python library
Remember to save a copy of the circuit before changing it!
There are lots of confusing solutions out there.