Project Logs

Collapse

• Temperature Overshoot in Hot Air Control – Implementing Software Tapering

  Srinivasan M S • 2 hours ago • 0 comments

  During initial testing of the temperature control system, a noticeable overshoot was observed when the heater approached the set temperature.

  The system uses PID-based control with thermocouple feedback. While the steady-state regulation was reasonably stable, the heating phase exhibited a tendency to exceed the target temperature before settling back.

  This behavior was more pronounced at higher temperature settings and during rapid heating cycles.

  Initial investigation suggested that the issue was not with sensor accuracy, but with the control response near the setpoint. The heater, being a relatively high-power element, continued to deliver residual heat even after the control output was reduced.

  To address this, a simple software-based tapering approach was introduced.

  Instead of allowing full control output until the setpoint is reached, the system gradually reduces heater drive as the temperature approaches the target. This effectively softens the control action near the setpoint and reduces thermal inertia effects.

  After implementing this change:

  • Temperature overshoot was significantly reduced

  • Settling time improved

  • Control behavior became more predictable

  This approach proved to be effective without requiring major changes to the PID parameters.

  It highlights the importance of considering system dynamics and thermal inertia in addition to pure control loop tuning.

  Would be interested to know how others handle overshoot in similar thermal control systems.

• Power Supply Debugging – Resolving 7812 Dropout and System Instability

  Srinivasan M S • a day ago • 0 comments

  During the initial testing phase, the system exhibited unstable behavior, particularly when the fan and control electronics were operating simultaneously.

  The 12V rail, derived using a linear regulator (7812), showed noticeable voltage drop under load. This resulted in erratic system operation, including unreliable fan startup and inconsistent control behavior.

  At first, the issue was suspected to be related to firmware timing or PWM interaction. However, further measurements revealed that the root cause was insufficient bulk capacitance on the rectified DC supply.

  The original design used a 1000 µF reservoir capacitor, which proved inadequate for handling transient load demands from the fan and control circuitry. Under load, the input voltage to the 7812 regulator dropped below its required dropout margin, causing the regulated 12V rail to sag to approximately 10.6V.

  To resolve this, the reservoir capacitance was increased from 1000 µF to 5000 µF. This significantly improved voltage stability by reducing ripple and maintaining sufficient headroom for the regulator during peak load conditions.

  After this modification:

  • The fan started reliably across the full PWM range

  • The control system became stable

  • Temperature regulation operated consistently

  This debugging process highlighted the importance of proper power supply design, especially in systems combining high-power loads with sensitive control electronics.

  Ensuring adequate bulk capacitance and understanding regulator limitations are critical for stable operation.

View all 2 project logs