The Proportional/Integral/Derivative controller or PID controller or just PID, is a proccess' control techinics that join Proportional integral and Derivative actions, thus causing the error signal is minimized by proportional action, integral action and cleared by a speed obtained with the preemptive derivative action.
It is based on mathematical modeling of the response of a loop process to be controlled.
In practice the PID controllers are found inside electronic controllers called "single-loop", often with microprocessors, and also through software on programmable logic controllers (PLC) and other control equipment.
In this project, we will simulate a brightness control with Arduino.
The Arduino will be running the PID library which can be found at:
In addition to the PID library for Arduino, will also need the PID Front End for processing, which is a GUI in order to configure the control parameters, such as P, I, D, Set Point and ways of working, etc. .. .; performing a user-friendly interface with Arduino.
You can also download the PID_FrontEnd from the link above.
As we will work with Arduino and Processing, we need to have the Arduino's IDE and Processing 1.0.1 2.0b8 installed in our computer.
To the Processing software, run properly with PID_FrontEnd, we also need the library "ContorlP5" for Processing installed in our computer.
You can Download the library "ControlP5" directly from the related link below:
For details on PID control processes, I advise you to visiting the PID_V1 Library's creator website.
Also access the "Control Guru" website for more details about automation and control.
Details about "Control Systems" can be found in the website:
Step 1: Constructive Aspects - Part One
We will do two tests, one with the simulated environment by a dark tube (this environment will not allow interference from outside), and another test with the open environment, where we can interfere externally and thus, verify the system response.
Test - 1
The environment is simulated by a dark tube (black).
At one end of the tube, we will have a white LED with high-brightness (it will be used to illuminate the environment). At the other end of the tube, we will have a LDR (the LDR will be used to manage the amount of light in the environment, it will be our system's feed back).
The connection with the Arduino is very simple:
The pin D3 (digital 3) of the Arduino will be used as output and is connected to the LED's anode. The LED has a resistor of 220 Ohms in series with the anode (for the LED's polarization); the LED's cathode is directly connected to GND.
The pin A0 (analog 0) of the Arduino will be connected to the LDR and used as analog input. The LDR has one leg connected directly to the +5 V supply, and the another leg of the LDR is connected to a pull-down resistor value of 10K (the resistor will be connected in series with the LDR and connected to the GND. At the intersection of the LDR + resistor we will have the output signal of the light sensor that will be connected to the Arduino's pin A0.
Look at the pictures to know how to do the circuit interconnection of sensors and actuators with Arduino, the circuit was designed with Fritzing.
Step 2: Constructive Aspects - Part Two
Now the system may suffer external actions which are called disturbances such as shading or excessive light in the sensoror in the environment or even blocking the sensor.
The disturbances are automatically controlled by the Arduino_PID, ie:
When we have a decrease of the incident light on the LDR (simulated by a shadow on LDR), the system will automatically increase the brightness of the LED trying to maintaining a constant ambient lighting.
When we have an increase of the incident light on the LDR (a flashlight may increase the brightness for simulation purposes), the system will reduce the brightness of the LED trying to maintaining a constant ambient lighting.
Another detail of this particular test is that the Setpoint value, is controlled by a potentiometer, is no longer needed to using the Setpoint configuration via PID_FrontEnd.
In the pictures, we have the circuit of sensors and actuator's interconnection with Arduino.
Step 3: Programming Aspects
1 - Download and unzip the libraries:
PID_V1 to the libraries' directory of the Arduino IDE;
Front End PID to a folder on your computer;
ControlP5 to the Processing Libraries' directory.
2 - Start the Arduino IDE and open the file "PID_FrontEnd_ArduinoSampleCode" from the "PID_FrontEnd" folder.
Send this scketch for arduino.
3 - Start the "Processing" and open the file "PID_FrontEnd_v03" from the PID_FrontEnd folder.
Run the application.
Look at the some pictures related to the process described above:
For the second test, in particular; we must send to the Arduino, the sketch below:
(this sketch will be used in place of the file "PID_FrontEnd_ArduinoSampleCode")
You can download this sketch from the link below.
Remembering that the Setpoint control value is done by a potentiometer.
As a disturbance source, we can use a flashlight to focus more light in the LDR or a little screen to shade the LDR.
When we have a disturbance in the process, the controller will increase / decrease the brightness of the LED trying to keeping the output under control and at the level settled by the setpoint (in the case of making a "shadow", the controller will increase light intensity of the LED), we can see these changes in PID_FrontEnd graphically.
Step 4: PID FrontEnd GUI
In this window, we can note the following functions:
TOGGLE_AM - changes the PID mode to automatic or manual;
SETPOINT - desired amount of light in the environment(from 0 to 1024);
INPUT - the actual value of the ambient brightness (measured by LDR and returned as feedback);
OUTPUT - the control value returned by the Arduino as a PID controller (brightness control of the LED attached on pin D3);
Kp - Proportional control's constant;
Ki - Integral control's constant;
Kd - Derivative control's constant;
TOOGLE_DR - changes the PID's direction (if output grows as grows the entry or the reverse of it);
SEND_TO_ARDUINO - send data to the Arduino;
PID Input / Setpoint - Graphical Window for the setpoint (desired value for brightness) and input (measure of brightness LDR) curves.
PID Output - Graphical window for the control output of the LED.
In the pictures, we can notice the setpoint settled to 950 (green line), the input variable (red line) and the PID control output variable (blue line) to control brightness.
We can understand the information described acimas through a block diagram (look at the pictures).
Where we note that the Error = SP - PV and the error is applied to the PID controller that generates the MV for process control.
PV = Proccess Variable;
SP = Set Point;
MV = Manipulated Variable.
Each controller type: P, I and D can be used independently or jointly as:
P controller (very used)
PI controller (very used)
PD controller (rarely used)
PID controller (most used)
Look at the pictures and you can observe a change in the setpoint value (from 950 to 700 and then to 950 again) and you can see the performance of PID control on the input variable.
You can observe that has a bit of oscillation in control (characteristic of each controlled system, whether it is first or second order, etc.).
Step 5: Videos
Again, I apologize, but the videos are in Portuguese. Please use the youtube caption that is translated into English.