While developing the temperature control system for the rework station, firmware-based control using PID regulation provided stable and predictable operation under normal conditions.

However, relying solely on firmware for safety was considered insufficient for a system involving a high-power heating element.

Potential failure scenarios were evaluated, including:

• Microcontroller hang or crash
• Software bugs affecting control logic
• Sensor failure or disconnection
• Unexpected operating conditions

In any of these cases, the heater could remain energized without proper regulation, leading to uncontrolled temperature rise.

To mitigate this risk, an independent hardware-based safety mechanism was incorporated.

The design ensures that, regardless of firmware state, the heater operation is constrained by hardware conditions. This includes enforcing safe operating limits and preventing continuous heating in abnormal situations.

Additionally, a fan–heater interlock was implemented to ensure that the heater cannot operate without adequate airflow. This prevents localized overheating and protects both the heating element and surrounding components.

By separating safety mechanisms from firmware control, the system achieves an additional layer of protection.

After implementing hardware safety:

• System resilience improved significantly
• Failure modes became more predictable and controlled
• Risk of overheating due to firmware issues was minimized

This approach reflects a general design principle in power electronics and embedded systems:

Critical safety functions should not depend solely on software.

Combining firmware control with independent hardware safeguards provides a more robust and fail-safe system.

Would be interested to know how others approach safety design in similar high-power embedded systems