Temperature Control PID

Why PID is Important

PID is crucial for stable temperature control.

Without PID, a simple way to control temperature would be:

If temperature too cold, turn heater on
If temperature too hot, turn heater off

But there is a big problem with that method.

Due to temperature not traveling instantly from the heater to the thermistor, when the thermistor reads a given temperature, the heater is already hotter than what the thermistor reads.

This overshooting is something we do not want.

It means reaching temperatures that could be undesirable, and it means you will not be able to correctly stabilize the temperature.

What is PID?

The solution to this is PID.

It uses some math, allowing us to correct those problems by turning the heater on and off in a smarter sequence.

PID stands for:

Proportional - Responds to current error
Integral - Responds to accumulated error over time
Derivative - Responds to rate of change of error

Configuring PID Values

The P, I, and D factors are configured in your config file as follows:

temperature_control.hotend.p_factor     100
temperature_control.hotend.i_factor     0.1
temperature_control.hotend.d_factor     100

Important: Do not try to use PID settings from Marlin as they are not compatible. Smoothie uses different PID algorithms and the values will not translate directly.

Finding the Right Values

The really tricky thing is to find the right values for these 3 factors.

The default ones are most probably wrong for your setup.

So unless you have been given those values with your hardware, or you are a PID grand-master, you will need some help finding the optimal values.

PID Auto-Tuning

Recommended Method: Use Smoothie's built-in PID auto-tuning feature to automatically calculate optimal PID values for your hardware.

To auto-tune your PID values:

Start the auto-tune process:
```
M303 E0 S200
```
- E0 specifies the hotend (use E1, E2, etc. for other extruders)
- S200 is the target temperature (adjust to your typical printing temperature)
Wait for completion - The process will take several minutes as it cycles the heater and measures response
Review the results - The auto-tune will output the calculated PID values
Update your config - Add the new values to your config file
Test - Heat to your target temperature and verify stability

Manual PID Tuning

If auto-tuning doesn’t work well for your setup, you can manually tune:

Starting Values

Begin with conservative values:

p_factor = 100
i_factor = 0.1
d_factor = 100

Tuning Process

Adjust P first:
- Too low: Slow to reach temperature, large oscillations
- Too high: Fast oscillations, unstable
Then adjust I:
- Too low: Won’t eliminate steady-state error
- Too high: Overshoots, slow to stabilize
Finally adjust D:
- Too low: More overshoot
- Too high: Very sensitive, noisy

Tip: Make small adjustments (10-20% at a time) and test thoroughly after each change. Monitor temperature graphs to see the effect of your changes.

Different Heater Types

Different heater configurations may require different tuning approaches:

High-Power Heaters

High-power heaters (like cartridge heaters) may need:

Lower P values
Higher D values
Faster response times

Low-Power Heaters

Low-power heaters (like resistive wire) may need:

Higher P values
More integral action
Slower response tuning

Heated Beds

Heated beds typically need:

Much lower P values due to large thermal mass
More integral action for steady-state
Lower D values due to slow thermal response

Troubleshooting PID Issues

Temperature Oscillates

Symptom: Temperature swings up and down around target

Solutions:

Reduce P factor
Increase D factor
Check for good thermal coupling between heater and thermistor

Slow to Reach Temperature

Symptom: Takes a long time to heat up

Solutions:

Increase P factor
Check PWM frequency settings
Verify heater power is adequate

Overshoots Temperature

Symptom: Temperature goes past target then settles

Solutions:

Reduce P factor
Increase D factor
Reduce I factor

Won’t Stabilize

Symptom: Can’t maintain steady temperature

Solutions:

Increase I factor slightly
Check for environmental factors (drafts, etc.)
Verify thermistor is working correctly

Advanced Configuration

PWM Frequency

The PWM frequency can affect PID performance:

temperature_control.hotend.pwm_frequency    1000

Higher frequencies (1000-4000 Hz) are typically better for solid-state relays and MOSFETs.

Bang-Bang Mode

For very simple setups, you can disable PID entirely:

temperature_control.hotend.bang_bang    true

This uses simple on/off control. Not recommended for most applications.

Safety Notes

Safety Warning:

Never leave heaters unattended during PID tuning
Ensure thermal runaway protection is enabled
Monitor temperatures closely during tuning
Have a fire extinguisher nearby
Stop immediately if anything seems wrong