A game that uses High Voltage to "zap" players. A player is picked at random and zapped uisng some flyback high voltage transformers of low power. The case is 3D printed, it uses rechargable batteries with a TP4056 charger, it has a speaker and DF player for sounds and addressable LEDs.

Homemade fully portable soldering iron with a battery inside taht could melt solder in under 10 seconds. See the schematic, the code and the PCB and make a digital soldering ironj yourself It is also based on Arduino and you can always improve the code.

Learn all the blocks of the Arduino internal ADC. All the registers and bits and how to make a measurement. Also how to use the internal temperature sensor.

Solder SMD components on the PCB with solder paste and the stencil using this homemade Reflow hot palte made with a chlotes iron and a solid state relay.

Homemade 7 channel Radio controller with STM32 microcontroller and the NRF24 radio module. It has a 3D printed case and NEXTION touchscreen.

Automatic solder paste dispenser with Arduino, a DC motor with gear and OLED display to select the time and amount of paste to push out. The case is 3D printed.