For those of you who are not sure how the PID settins are expressed in the Mypin let me explain. Maybe this will help out anyone that has a mypin and are trying to get their process dialed in.
With the Mypins the proportional gain is expressed in degrees, not percent like some other controllers. This means that if integral and derivative are both turned off (zero) and proportional gain is set to 5 °F on a cold start your system will fire at 100% output until the process variable (PV) reaches within 5 °F of the setpoint value (SV). Once the temperature (PV) reaches within 5 °F of the SV the output will begin to taper off. For example, once the PV is within 2.5 °F of the setpoint the output will be at 50% and once the PV reaches setpoint the output should be 0%. I think this is where people with mypins are getting hung up. The controller is still outputing after the setpoitn has been reached/exceeded. This simply should not be happening. But I digress.
The problem with only using proportional gain to control at setpoint is that once the setpoint is reached the output is reduced to 0%. On really fast systems with constantly changing PVs that may be OK but on homebrew systems, we need some integral to maintain the setpoint.
Integral is typically expressed in seconds per reset (S/R) or resets per minute (R/M). Mypins express integral in seconds per reset. So if you set your integral to 60 on a mypin you will be capable of achieving 1 reset per 60 seconds. If you set it to 30 you will achieve 1 reset in 30 seconds, or 2 resets per minute. The more resets per minute, the faster your system will be able to react.
Don't worry about Derivative. It likely won't benefit your homebrew system enough to bother dialing in the proper setting. The proper P and I settings will get you where you need to be.