It features over 5,400 projects, ranging from simple tutorials — like using a soil moisture sensor with Arduino — to more complete guides like building a Bluetooth-controlled car.

Most already come complete with the UNO board and a bunch of components like LEDs, a temperature sensor, a DC motor, a servo motor, and an LCD module. Then, there's the matter of the power supply.

The input circuit is a simple keypad matrix. To read each button push, the Arduino brings one keypad input line high and checks the voltage of the four output lines in order.