| Sensor pin | Connects to | Note |
|---|---|---|
| VCC | 5V | Power |
| GND | GND rail | Ground |
| Trig | A1 PA1 | Output |
| Echo | A7 PA2 | Input |
| LCD pin | Connects to | Note |
|---|---|---|
| 1 VSS | GND rail | Ground |
| 2 VDD | 5V | Power |
| 3 V0 | Pot wiper | Contrast |
| 4 RS | A5 PA6 | Register select |
| 5 RW | GND rail | Write-only |
| 6 EN | A6 PA7 | Enable |
| 7–10 | N/C | Not used |
| 11 D4 | D9 PA8 | Data bit 0 |
| 12 D5 | D10 PA11 | Data bit 1 |
| 13 D6 | D11 PB5 | Data bit 2 |
| 14 D7 | D12 PB4 | Data bit 3 |
| 15 A (BL+) | 5V | Backlight + |
| 16 K (BL−) | GND rail | Backlight − |
| Pot pin | Connects to | Note |
|---|---|---|
| Left | 5V | High reference |
| Middle (wiper) | LCD pin 3 | Contrast out |
| Right | GND rail | Low reference |
| Component pin | Connects to | Note |
|---|---|---|
| Gate (G) | A2 PA3 | ~100 Ω series |
| Gate (G) | GND rail | 10k–100 kΩ pull-down |
| Drain (D) | Buzzer − | Switched output |
| Source (S) | GND rail | Direct to ground |
| Buzzer + | 3.3V | Power |
| Buzzer − | MOSFET Drain | Switched by FET |
| Diode cathode ▌ | 3.3V | Same node as Buzzer + |
| Diode anode | MOSFET Drain | Same node as Buzzer − |