I want to heat a small volume of water (~15 mL) using a waterproof heating pad (Electric Heating Pad - 10cm x 5cm : ID 1481 : $3.95 : Adafruit Industries, Unique & fun DIY electronics and kits) and temperature probes (DS18B20). I have a good grasp of the math behind PID, and Arduino's PID(&Input, &Output, &Setpoint, Kp, Ki, Kd, Direction) is easy enough to use. However, I need to know:
What does MOSFET do, and how do I use it? Lot's of PID posts mention this.
Does PID require analog input and output? Are my parts analog?
What parts need resistors, and what principles should I follow to choose their values?
I am inexperienced with circuitry, so thanks for everyone's help. I realize my questions may be broad, so providing links to read is fine.