Gather the Datasheet Information
• Locate the HC-SR04 datasheet (pin configuration, dimensions, electrical characteristics).
• Identify the key pins (typically VCC, Trig, Echo, and GND).

Create a Custom Schematic Symbol
• In Flux, open the custom part or schematic symbol editor.
• Draw the symbol to represent the HC-SR04.
• Place pins for VCC, Trig, Echo, and GND and label them accordingly.
• Optionally, add necessary annotations or datasheet references.

Design a Custom Footprint
• Open the PCB footprint editor in Flux.
• Use the dimensions from the datasheet to lay out the pads corresponding to the HC-SR04 sensor.
• Set the pad sizes, spacing, and any silkscreen markings as needed.

Link the Symbol and Footprint
• Once both symbol and footprint are created, link them together to form the complete custom part.
• Double-check that the pin names and numbers match between the schematic symbol and the footprint.

Save and Add to Your Project
• Save the newly created part in your personal library within Flux.
• Add the custom HC-SR04 part to your schematic, and verify that it appears with the correct symbol and footprint.

Test the Part in Your Design
• Place and wire the HC-SR04 in your schematic.
• Verify (using the design rules in Flux) that the custom part integrates correctly into your project.