Designing PCB layouts from scratch (Eagle, KiCAD). - digital electronics (STM32, Arduino/Atmega328, NRF51/52 series) - power electronics/electromechanical (DC-DC, AC-DC (up to 1kV), charging, relays) - analog electronics - wireless and rf (BLE, radio, Wi-Fi, NFC/RFID) - DC motor controllers - LEDs and sound