Electronics 01
How to Drive a Relay or Motor from Arduino with a Transistor
Wire a relay, DC motor or 12 V LED strip to an Arduino or ESP32 pin with a PN2222A or a MOSFET: base resistor math, flyback diode, pin limits and heat.
esp32
Electronics 02
5V to 3.3V With a Voltage Divider (and When Not To)
Step a 5 V signal down to 3.3 V with two resistors: which values to use, the E24 pairs, how loading and pin speed limit it, and when you need a regulator.
Electronics 03
What Resistor for an LED on Arduino 5V and 3.3V?
Resistor values for every LED colour on Arduino 5V and ESP32 3.3V pins, with the pin limits, worked examples and why a white LED on 3.3V is a trap.