ARDUINO UNO R3 CONNECTIONS

HC-SR04 ULTRASONIC SENSOR
Arduino 5V    -> HC-SR04 VCC
Arduino GND   -> HC-SR04 GND
Arduino D9    -> HC-SR04 TRIG
Arduino D10   -> HC-SR04 ECHO

0.96-INCH 4-PIN SSD1306 OLED (5V-compatible version only)
Arduino 5V    -> OLED VCC
Arduino GND   -> OLED GND
Arduino A4    -> OLED SDA
Arduino A5    -> OLED SCL

RED LED
Arduino D6    -> 220 Ohm resistor -> LED ANODE (+)
Arduino GND   -> LED CATHODE (-)

All components share a common GND.
NOTE: Check the OLED's operating voltage, pin labels and I2C address.
