Hi everyone, today I’m gonna show you how to use a photoresistor to regulate the luminosity intensify of a led.
The technique is called PWM and permit you to modify the wave’s duty cycle.
Modulating the duty cycle that is the proportion of “on” time to the “period” of time, you can regulate correspondent power.
Duty Cycle is expressed in percent, so 50% of duty cycle will mean that you will have Period/2 ms with “On” state and Period/2 ms with “Off” state. You will you get an analog result on the output with digital mean.
The voltage will be between 0V and 5V
With this approach, when it becomes dark, the led will be brighter.
Vice-versa when it becomes light, the led will be darker.
Below you can see what correspond our circuit; our photoresistor is like a variable resistor that will variate the voltage analog input on Arduino board.
This is the schematic that I designed with Fritzing program and what you should wire to replicate this project.
With Proteus Program, I wanted to simulate our circuit using these components:
- Arduino board
- Led-Red
- A resistor of 220 Ohm
- An Oscilloscope to watch the wave’s form.
- A com port terminal
- A Debug Terminal for the com port.
- A variable resistor to simulate our photoresistor.
- A voltage multimeter to measure voltage across variable resistor.
This is the source code you have to deploy into Arduino board.
It is necessary to “stretch” a variable that varies from 0 to 1023 (Analog Input Variable) into a variable that varies from 0 to 255(Analog Output Variable).
You can do this using the function called “map”. The implementation of this function is the following code:
0 1 2 3 | long map(long x, long in_min, long in_max, long out_min, long out_max) { return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min; } |
You can find the description of the function here:
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | .void setup() { /* add setup code here */ //pinMode(7, OUTPUT); analogReference(DEFAULT); Serial.begin(9600); } void loop() { int value; /* add main program code here */ value = analogRead(0); //Serial.println(value); value = map(value, 0, 1023, 0, 255); value = constrain(value, 0, 255); analogWrite(7, value); Serial.println(value); } |
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 | function varargout = GUIMatlab(varargin) % GUIMATLAB MATLAB code for GUIMatlab.fig % GUIMATLAB, by itself, creates a new GUIMATLAB or raises the existing % singleton*. % % H = GUIMATLAB returns the handle to a new GUIMATLAB or the handle to % the existing singleton*. % % GUIMATLAB('CALLBACK',hObject,eventData,handles,...) calls the local % function named CALLBACK in GUIMATLAB.M with the given input arguments. % % GUIMATLAB('Property','Value',...) creates a new GUIMATLAB or raises the % existing singleton*. Starting from the left, property value pairs are % applied to the GUI before GUIMatlab_OpeningFcn gets called. An % unrecognized property name or invalid value makes property application % stop. All inputs are passed to GUIMatlab_OpeningFcn via varargin. % % *See GUI Options on GUIDE's Tools menu. Choose "GUI allows only one % instance to run (singleton)". % % See also: GUIDE, GUIDATA, GUIHANDLES % Edit the above text to modify the response to help GUIMatlab % Last Modified by GUIDE v2.5 27-Feb-2018 11:51:54 % Begin initialization code - DO NOT EDIT gui_Singleton = 1; gui_State = struct('gui_Name', mfilename, ... 'gui_Singleton', gui_Singleton, ... 'gui_OpeningFcn', @GUIMatlab_OpeningFcn, ... 'gui_OutputFcn', @GUIMatlab_OutputFcn, ... 'gui_LayoutFcn', [] , ... 'gui_Callback', []); if nargin && ischar(varargin{1}) gui_State.gui_Callback = str2func(varargin{1}); end if nargout [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:}); else gui_mainfcn(gui_State, varargin{:}); end % End initialization code - DO NOT EDIT % --- Executes just before GUIMatlab is made visible. function GUIMatlab_OpeningFcn(hObject, eventdata, handles, varargin) % This function has no output args, see OutputFcn. % hObject handle to figure % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) % varargin command line arguments to GUIMatlab (see VARARGIN) % Choose default command line output for GUIMatlab handles.output = hObject; % Update handles structure guidata(hObject, handles); % UIWAIT makes GUIMatlab wait for user response (see UIRESUME) % uiwait(handles.figure1); instrreset; global s; s=serial('COM4','BaudRate',9600); fopen(s); % --- Outputs from this function are returned to the command line. function varargout = GUIMatlab_OutputFcn(hObject, eventdata, handles) % varargout cell array for returning output args (see VARARGOUT); % hObject handle to figure % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) % Get default command line output from handles structure varargout{1} = handles.output; % --- Executes on button press in StartButton. function StartButton_Callback(hObject, eventdata, handles) % hObject handle to StartButton (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) global s; i=0; adc=zeros(1,1000); while(i<1000) i=i+1; adc(i)=fscanf(s,'%d'); set(handles.ActualAnalogValue,'String',adc(i)); drawnow; axes(handles.axes1); plot(adc,'r.-','LineWidth',2); grid on; %axis([0 1000 0 300]); if i>999 i=0; end end function Analog_Actual_Value_Callback(hObject, eventdata, handles) % hObject handle to Analog_Actual_Value (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) % Hints: get(hObject,'String') returns contents of Analog_Actual_Value as text % str2double(get(hObject,'String')) returns contents of Analog_Actual_Value as a double % --- Executes during object creation, after setting all properties. function Analog_Actual_Value_CreateFcn(hObject, eventdata, handles) % hObject handle to Analog_Actual_Value (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles empty - handles not created until after all CreateFcns called % Hint: edit controls usually have a white background on Windows. % See ISPC and COMPUTER. if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor')) set(hObject,'BackgroundColor','white'); end function PWM_Actual_Value_Callback(hObject, eventdata, handles) % hObject handle to PWM_Actual_Value (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) % Hints: get(hObject,'String') returns contents of PWM_Actual_Value as text % str2double(get(hObject,'String')) returns contents of PWM_Actual_Value as a double % --- Executes during object creation, after setting all properties. function PWM_Actual_Value_CreateFcn(hObject, eventdata, handles) % hObject handle to PWM_Actual_Value (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles empty - handles not created until after all CreateFcns called % Hint: edit controls usually have a white background on Windows. % See ISPC and COMPUTER. if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor')) set(hObject,'BackgroundColor','white'); end % --- Executes on button press in StopButton. function StopButton_Callback(hObject, eventdata, handles) % hObject handle to StopButton (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) % --- Executes on key press with focus on Analog_Actual_Value and none of its controls. function Analog_Actual_Value_KeyPressFcn(hObject, eventdata, handles) % hObject handle to Analog_Actual_Value (see GCBO) % eventdata structure with the following fields (see MATLAB.UI.CONTROL.UICONTROL) % Key: name of the key that was pressed, in lower case % Character: character interpretation of the key(s) that was pressed % Modifier: name(s) of the modifier key(s) (i.e., control, shift) pressed % handles structure with handles and user data (see GUIDATA) % --- Executes during object creation, after setting all properties. function text4_CreateFcn(hObject, eventdata, handles) % hObject handle to text4 (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles empty - handles not created until after all CreateFcns called % --- Executes during object deletion, before destroying properties. function axes1_DeleteFcn(hObject, eventdata, handles) % hObject handle to axes1 (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) % --- Executes during object deletion, before destroying properties. function axes1_CreateFcn(hObject, eventdata, handles) % hObject handle to axes1 (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) % --- Executes during object deletion, before destroying properties. function axes1_ButtonDownFcn(hObject, eventdata, handles) % hObject handle to axes1 (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) function valoreattualeanalogico_Callback(hObject, eventdata, handles) % hObject handle to valoreattualeanalogico (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) % Hints: get(hObject,'String') returns contents of valoreattualeanalogico as text % str2double(get(hObject,'String')) returns contents of valoreattualeanalogico as a double % --- Executes during object creation, after setting all properties. function valoreattualeanalogico_CreateFcn(hObject, eventdata, handles) % hObject handle to valoreattualeanalogico (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles empty - handles not created until after all CreateFcns called % Hint: edit controls usually have a white background on Windows. % See ISPC and COMPUTER. if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor')) set(hObject,'BackgroundColor','white'); end % --- Executes during object creation, after setting all properties. function text6_CreateFcn(hObject, eventdata, handles) % hObject handle to text6 (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles empty - handles not created until after all CreateFcns called function ActualAnalogValue_Callback(hObject, eventdata, handles) % hObject handle to ActualAnalogValue (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) % Hints: get(hObject,'String') returns contents of ActualAnalogValue as text % str2double(get(hObject,'String')) returns contents of ActualAnalogValue as a double % --- Executes during object creation, after setting all properties. function ActualAnalogValue_CreateFcn(hObject, eventdata, handles) % hObject handle to ActualAnalogValue (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles empty - handles not created until after all CreateFcns called % Hint: edit controls usually have a white background on Windows. % See ISPC and COMPUTER. if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor')) set(hObject,'BackgroundColor','white'); end |
This is the Matlab code you have to run to simulate by yourself this tutorial 🙂
By reading serial port with Matlab I got this plot.
Enjoy!
Giuseppe 🙂
