I'd be curious to know how much the temperature fluctuates and what the average temperature is, plotted against the target. A simple on/of setup like this is much less complicated than a PID setup, but in my experience, the PID code would allow for a much more accurate temperature to be maintained.
In larger baths of water (I am using a half-filled 4.75 gallon container), the temperature only fluctuates ~0.25C from the setpoint, as measured by the sensor. I think the large quantity of water makes the change in temperature very gradual.
