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# PID_RT

Arduino library for PID controller.


## Description

The PID_RT class allows the user to instantiate a PID controller.


## Interface

### Constructor

- **PID_RT()** minimal constructor.
- **PID_RT(float sp, float Kp, float Ki, float Kd)** constructor that sets minimal parameters to get started.


### Core

- **void reset()** resets internals to startup.
- **void setPoint(float sp)** sets setPoint, that needs to be reached.
- **float getSetPoint()** read back setPoint.
- **bool  compute(float input)** does one iteration of the PID controller. 
Returns **true** after calculation. 
Returns **false** if not computed, either due to stop flag or not yet time to do the calculation.
- **float getOutput()** get the last calculated output value. 
- **bool  setK(float Kp, float Ki, float Kd)** Set the initial P I D parameters as a group.
Overwrites the values set in the constructor.


### Start Stop

- **void start()** enable the PID controller to **compute()** new output values.
- **void stop()** disable the PID controller, see **compute()**.
- **bool isRunning()** return the enable/disable flag.


### Behaviour parameters

- **bool setInterval(uint32_t interval)** set the interval between two **compute()** calls. 
Returns **true** if changed, otherwise **false**.
- **uint32_t getInterval()** read back interval set.
- **void setOutputRange(float rangeMin, float rangeMax)** tune the output range, default 0..100
- **float getOutputMin()** read back setting rangeMin.
- **float getOutputMax()** read back setting rangeMax.
- **void setReverse(bool reverse)** reverse behaviour, seldom needed.
- **bool getReverse()** read back the setting.


### K-parameters

- **bool setKp(float Kp)** runtime updates are allowed - at your own risk.
- **bool setKi(float Ki)** runtime updates are allowed - at your own risk.
- **bool setKd(float Kd)** runtime updates are allowed - at your own risk.
- **float getKp()** read back setting.
- **float getKi()** read back setting.
- **float getKd()** read back setting.


### Proportional

- **void setPropOnInput()** this is default behaviour.
- **void setPropOnError()** alternative.
- **bool isPropOnInput()** read back setting.
- **bool isPropOnError()** read back setting.


### debugging calls

- **float getInput()** read last input.
- **float getLastError()** read the last error.
- **uint32_t getLastTime()** get the last time **compute()** was called.
Note this value is incremented with **Interval** every iteration so it 
may have some offset of the actual time. This is chosen as this way it is 
almost sure that no iterations are missed. 


## Operations

See examples.


## Future

#### must

- update / improve documentation
- more testing

#### should

- add examples to test more
- improve unit test
- move all code to .cpp

#### could

- add reference to PID book / website?
- investigate if it works as PI or P controller too.
  - PI as derived or base class?