ESP32 Thing Plus Hookup Guide - WRL-15663 by SparkFun Electronics Datasheet
Paul's DIY electronics blog: 2016
optically isolated and debounced 24V switch input
understanding GPIO circuits - Raspberry Pi Forums
5V To GND when button pushed? - General Electronics - Arduino Forum
Arduino Uno USB ground connected to ground pins - IDE 1.x - Arduino Forum
Button, why a connection to ground? - Noob questions - General Electronics - Arduino Forum
Review: Digilent Analog Discovery 2
Isolate PH Circuit - General Electronics - Arduino Forum
Arduino Camping LED Light with Dimmer
RAMPS 1.4 - RepRap