Magnetic Stirrer

1/*
2 Magnetic Stirrer
3 
4 Layman summary: 
5 We will use a potiometer  to control the speed of a DC motor.
6 When the potiometer is turned to full Ohms  then the motor should stop.
7 When the potiometer is turned to 0 Ohms then the  motor should be running full speed.
8 And if the potiometer is somewhere in the  middle then the motor speed will follow. 
9 
10 
11 InDepth summary;
12 This  code will read an analog voltage of the potiometer using pin(A0). 
13  We will  take the analog to digital conversion (ADC) value and 
14 produce a corresponding  PWM signal on pin(9). The PWM signal will turn the 
15 NPN transistor on/off very  quickly to the point where the motor will spin like
16 it is getting less than  full power. 
17 
18 Notes:
19 1. Please note the ADC on the Arduino mega is 10  bits. The PWM is 8 bits. 
20 So we need to divide the ADC value from pin(A0) by  4 and then send that value to 
21 the PWM on pin(9).  
22 
23 2. Intersting to  note that if you leave out the division then 
24 you will notice that a 1/4 turn  of the potiometer will give you a 0 rpm to full speed 
25 on your motor. This is  because 8 bits will get you 255 steps for the PWM and the 
26 ADC 10 bits will  give you 1023 steps. 1023/255 = 4 (roughly) 
27 
28 3. I added a delay at end  of loop to help stablize motor speed. I noticed
29 with PC fans I was using that  if you rotated the potiometere quickly or back and fourth
30 that the load of the  magnets and the drastic speed up/down would burn out the 
31 cheap PC fan motors.  So a word of caution is to turn the pot slowly to avoid motor burn out :)
32 
33  
34 Brief Function description: 
35 analogWrite() allows us to send a 0 to 255  value to a PWM pin. 
36 ReadAnalogVoltage() allows us to read a 0 to 5Vdc voltage  and convert
37 voltage into a value between 0 to 1023. 
38 Serial.Began starts  serial communication to "Serial Monitor" 
39 Serial.PrintLn writes one line to  "Serial Monitor"
40
41
42 Credits:
43 Giving credit to the contributors of  the example (basic) "Fade" program 
44 and "ReadingAnalogVoltage" program since  this code is really just a cut/paste of 
45 both example programs into one working  code.
46 
47 
48 leaving the original ReadAnalogVoltage notes since I found them  useful as well :) 
49   ReadAnalogVoltage
50  Reads an analog input on pin 0,  converts it to voltage, and prints the result to the serial monitor.
51  Graphical  representation is available using serial plotter (Tools > Serial Plotter menu)
52  Attach the center pin of a potentiometer to pin A0, and the outside pins to +5V  and ground.
53
54  This example code is in the public domain.
55 */
56
57
58int  motor1 = 9;           // the PWM pin 
59int motor1speed = 0;    // how fast motor1  is
60
61// the setup routine runs once when you press reset:
62void setup() {
63  // declare pin 9 to be an output:
64  pinMode(motor1, OUTPUT);
65    // initialize  serial communication at 9600 bits per second:
66  Serial.begin(9600);
67}
68
69//  the loop routine runs over and over again forever:
70void loop() {
71  
72      //  read the input on analog pin 0:
73  int motor1speed = analogRead(A0);
74  
75    // Convert the analog reading (which goes from 0 - 1023) to a voltage (0 - 12V):
76  float voltage = motor1speed * (12.0 / 1023.0);
77  
78  // print out the value  you read:
79  Serial.println(motor1speed);
80  // print out the voltage 
81  Serial.println(voltage);
82  
83  // set the motor1speed of pin 9:
84  analogWrite(motor1, motor1speed/4);
85  
86  // delay 30 miliseconds. this pre
87  delay(30);
88}
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