Hobby Electronics Projects & More

Arduino Nano test circuit.Fig. 1

Arduino Motor Control Program Using IF

by Lewis Loflin

The two earlier tutorials will help with understanding this tutorial. See:

As a reminder of an "if" statement:

if (expression) true_do_this;
else false_do_this;

This tutorial will into more novel uses of the "if" statement.

We will create a motor control program for an Arduino. Note the diagram above.

Ill assume the output pins for LED1 and LED2 connect to separate DC motors with driver transistors or to one on my many H-Bridge circuits.

LED3 could be connected to a power ON-OFF circuit. Or just use the LEDs.

What we want is 1) S1 turns on LED1; 2) S2 turns on LED2; 3) S1 and S2 together turn on LED3 ON or OFF. LED1 and LED2 should be disabled while LED3 is toggling between ON-OFF.

All three LED pins (DP9, DP10, DP11) all have pulse-width modulation (PWM) function. I'll use the function POT() to control LED brightness or motor speed. We could even PWM the power ON-OFF LED3.

I created function S1(), S2(), and POT() and are included in the template at the bottom of the page. The template also incorporates an I2C LCD display displaying switch values (1 or 0) and the potentiometer reading on from ADC0 which is returned when POT() is called.

ON is defined as 1 or HIGH; OFF is defined as 0 or LOW.

void loop() {

  if ( POT() ) digitalWrite(LED1, ON);
  else digitalWrite(LED1, OFF);

Test 1

The function POT() reads the potentiometer connected to ADC0 on the Arduino. It returns an int value from 0-1023.

Observe line 2 of the LCD display "POT = 0" - set the control for 0. At position 0 POT() returns a 0 value when called making the "if" statement "false" turning OFF LED1.

Turn the potentiometer to any other value LED1 is ON. 1-1023 is interpreted as "true" thus LED1 is ON by the "if" statement except with 0.

The following line does the very same thing:

  if ( POT() != 0 ) digitalWrite(LED1, ON);
  else digitalWrite(LED1, OFF);

The following uses the NOT operator (!) to flip true to false, or false to true. Now LED1 is ON only at 0.

  if ( !POT() ) digitalWrite(LED1, ON);
  else digitalWrite(LED1, OFF);

The following turns on LED1 only when POT() is 700 or greater:

 if ( POT() >= 700 ) digitalWrite(LED3, ON);
 else digitalWrite(LED3, OFF);

The following turns on LED1 only when POT() is 700 or less:

 if ( POT() <= 700 ) digitalWrite(LED3, ON);
 else digitalWrite(LED3, OFF);

And so on Note the following comparison and Boolean operators:

Comparison Operators
== (equal to)
!= (not equal to)
< (less than)
> (greater than)
<= (less than or equal to)
>= (greater than or equal to)

Boolean Operators
&& (and)
|| (or)
! (not)

void loop() {
  if ( (POT() >= 400) && (POT() <= 800) ) digitalWrite(LED3, ON);
  else digitalWrite(LED3, OFF);
} // end loop

Test 2

In the above code snippet we use a logical AND symbol "&&". (A single & is a bitwise function and will produce an error.)

I'm checking "expression" for true and both MUST be true for the "if" statement to be true. POT() must return a value from 400 AND to 800 to turn on LED3.

I would suggest using individual parentheses for each "expression" inside the "if" parentheses. While in this case it compiled and worked fine, other times it could compile fine but be wrong.

With this in mind let us get to the good stuff.

Arduino motor test circuit.Fig. 2

Fig. 2 is my motor test setup. For either motor to run DP11 (LED3) must be ON turning on Q3.

DP9 (LED1) must be ON to turn on Q1 and MOT1 runs forward. DP10 (LED2) must be ON to turn on Q2 so MOT2 runs in reverse.

void loop() {

  if ( S1() && !S2() ) {
    if (S2()) { } // do nothing
    else digitalWrite(LED1, ON);
  else digitalWrite(LED1, OFF);

  if ( S2() && !S1() ) {
    if ( S1() ) { } // do nothing
    else digitalWrite(LED2, ON);
  else digitalWrite(LED2, OFF);
  if ( S1() && S2() ) {
    byte temp = !digitalRead(LED3);
    digitalWrite(LED3, temp);
    while( S1() || S2() ) { } // do nothing
  } // end if

  POT(); // update LCD display

} // end loop

Test 3

The above program uses two switches and has 3 outputs. Both S1 and S2 must be pressed together to enable motor power control Q3 ON or OFF.

Then either S1 or S2 will enable their respective motors. Both motors (or LEDs) can't be operated at the same time. Either S1 or S2 will check if the other switch is pressed and if it is the rest of the statement is skipped.

That is the purpose of "{ }" empty "do nothing" statement works somewhat like the "break" statement. Break doesn't work with the nested "if" statements.

If the power has not been enabled with Q3 neither motor will run.

void loop() {
  if ( S1() )   {
    digitalWrite(LED2, OFF);
    byte temp = !digitalRead(LED1);
    digitalWrite(LED1, temp);
    // wait for switch open
    while ( S1() ) { }
  } // end if

  if ( S2() )   {
    digitalWrite(LED1, OFF);
    byte temp = !digitalRead(LED2);
    digitalWrite(LED2, temp);
    // wait for switch open
    while ( S2() ) { }
  } // end if
  // this line acts as motor speed control
  analogWrite(LED3, POT() / 4);

} // end loop

Test 4

Program 4 above will toggle either motor ON-OFF. But motor speed is controlled through Q3 (LED3) circuit. If sketch has the LCD display the POT() value should be displayed.

If one motor is already ON it will be turned OFF as the new motor is turned on.

My YouTube Videos on Electronics
Introduction to the Arduino Microcontroller
Part 1: Programming Arduino Output
Part 2: Programming Arduino Input
Part 3: Arduino Analog to Digital Conversion
Part 4: Using Arduino Pulse-Width-Modulation
Repost Arduino AC Power Control