The hardware design principles for microcontrollers are as follows:

1. Functionality: Ensure that the microcontroller hardware meets all the functional requirements specified for the target application.

2. Power Supply: Provide a stable and appropriate power supply to the microcontroller and its peripherals. Use proper decoupling capacitors to filter out noise.

3. Clock System: Design a reliable and accurate clock system to generate the required clock signals for the microcontroller and its peripherals.

4. I/O Interfaces: Design the input/output interfaces to accommodate the necessary external connections for communication with other devices and components.

5. Peripheral Integration: Properly integrate and configure additional peripherals like ADC (Analog-to-Digital Converter), UART (Universal Asynchronous Receiver-Transmitter), PWM (Pulse Width Modulation), etc., as per the application's requirements.

6. Reset and Initialization Circuitry: Implement a robust reset circuit to ensure a reliable start-up and initialization process for the microcontroller.

7. Memory Configuration: Plan the memory layout, including ROM, RAM, and any external memory components required for storing program code and data.

8. Grounding and Signal Integrity: Pay attention to grounding and signal integrity practices to minimize noise, interference, and signal loss.

9. Protection Circuitry: Incorporate protective measures like over-current protection, reverse polarity protection, and ESD (Electrostatic Discharge) protection to safeguard the microcontroller from potential damage.

10. Testability and Debugging: Include necessary features to facilitate testing and debugging of the microcontroller and its connected components.

11. Power Efficiency: Optimize power consumption to prolong battery life and reduce overall energy usage.

12. Electromagnetic Compatibility (EMC): Ensure that the microcontroller hardware design complies with electromagnetic compatibility standards to avoid interference with other devices.

13. Size and Cost Considerations: Keep the physical size and cost of the microcontroller hardware within acceptable limits for the target application.

14. Future Expandability: Allow room for future expansion or upgrades to accommodate potential enhancements or additional features.

15. By following these hardware design principles, you can develop a reliable and efficient microcontroller-based system for various applications.