Motor speed control with PWM in Arduino - Step-by-Step Execution

Concept Flow - Motor speed control with PWM

Start

↓

Setup PWM Pin

↓

Set PWM Value (0-255)

↓

Write PWM to Motor Pin

↓

Motor Speed Changes

↓

Loop or Update PWM

↩Back to Set PWM Value

The program sets up a PWM pin, writes a value between 0 and 255 to control motor speed, then loops to update speed as needed.

Execution Sample

Arduino

int motorPin = 9;
void setup() {
  pinMode(motorPin, OUTPUT);
}
void loop() {
  analogWrite(motorPin, 128); // half speed
}

This code sets motorPin as output and writes a PWM value of 128 to run the motor at half speed.

Execution Table

Step	Action	PWM Value	Motor Speed Effect
1	Setup motorPin as OUTPUT	N/A	Motor ready to receive PWM
2	Write PWM value 128 to motorPin	128	Motor runs at about 50% speed
3	Loop repeats, PWM stays 128	128	Motor speed remains steady
4	If PWM changes (e.g., 255)	255	Motor runs at full speed
5	If PWM changes (e.g., 0)	0	Motor stops
6	End of loop iteration	N/A	Ready for next PWM update

💡 Loop runs continuously; motor speed updates whenever PWM value changes

Variable Tracker

Variable	Start	After Step 2	After Step 4	After Step 5	Final
motorPin	9	9	9	9	9
PWM Value	N/A	128	255	0	0

Key Moments - 3 Insights

Why does the motor speed change when PWM value changes?

Because PWM value controls the power sent to the motor; higher PWM means more power and faster speed (see execution_table steps 2, 4, 5).

What happens if PWM value is 0?

The motor stops because no power is sent (execution_table step 5 shows PWM 0 means motor speed stops).

Why do we use analogWrite instead of digitalWrite?

analogWrite sends a PWM signal to control speed smoothly, while digitalWrite only turns motor fully ON or OFF.

Visual Quiz - 3 Questions

Look at the execution_table, what PWM value makes the motor run at half speed?

A 128

B 255

C 0

D 64

💡 Hint

Check step 2 in the execution_table where PWM value 128 corresponds to half speed

At which step does the motor stop running?

A Step 2

B Step 4

C Step 5

D Step 3

💡 Hint

Look at step 5 in execution_table where PWM is 0 and motor speed stops

If PWM value changes from 128 to 255, what happens to motor speed?

A Motor speed stays the same

B Motor speed increases to full speed

C Motor speed decreases

D Motor stops

💡 Hint

See step 4 in execution_table where PWM 255 means full speed

Concept Snapshot

Motor speed control with PWM:
- Use analogWrite(pin, value) where value is 0-255
- 0 means motor off, 255 means full speed
- PWM controls power by switching ON/OFF rapidly
- Setup pin as OUTPUT before writing PWM
- Loop to update speed dynamically

Full Transcript

This example shows how to control motor speed using PWM on an Arduino. First, the motor pin is set as an output. Then, analogWrite sends a PWM signal with a value between 0 and 255. A value of 128 runs the motor at half speed, 255 at full speed, and 0 stops the motor. The loop repeats to keep the motor running or update speed. PWM controls motor power by turning the pin on and off quickly, changing the average voltage and thus speed.