View source for DC Motor with Encoder

{{DISPLAYTITLE:Arduino Motor RPM Measurement Using LM393 Encoder}}

{| class="wikitable" style="float:right; margin-left:20px; width:300px;"
! colspan="2" style="font-size:120%;" | Motor RPM Measurement
|-
! Controller
| Arduino
|-
! Motor Driver
| L293D
|-
! Encoder
| LM393
|-
! Encoder Disc
| 20 slots
|-
! Encoder Position
| Gearbox output shaft
|-
! Output
| RPM
|}

'''Arduino Motor RPM Measurement''' is a simple motor-control and speed-measurement setup using an Arduino, L293D motor driver and LM393 optical encoder.

The '''20-slot encoder disc''' is mounted on the '''gearbox output shaft'''. Therefore:

<center>
'''20 pulses = 1 output-shaft revolution'''
</center>

The Arduino controls the motor and counts encoder pulses for one second to calculate the output-shaft RPM.

== Connections ==

{| class="wikitable"
! Device
! Pin
! Arduino
! Function
|-
| LM393
| DO
| D2
| Encoder pulse
|-
| LM393
| VCC
| 5V
| Power
|-
| LM393
| GND
| GND
| Ground
|-
| L293D
| EN1
| D5
| Motor PWM
|-
| L293D
| IN1
| D7
| Motor direction
|-
| L293D
| IN2
| D8
| Motor direction
|}

=== Motor direction ===

<syntaxhighlight lang="cpp">
IN1 = HIGH
IN2 = LOW
</syntaxhighlight>

=== Encoder ===

The LM393 produces a digital pulse whenever a slot on the encoder disc passes the sensor.

<syntaxhighlight>
20 slots
   ↓
20 pulses
   ↓
1 output-shaft revolution
</syntaxhighlight>

== Working ==

The motor is driven through the L293D. The encoder disc rotates together with the gearbox output shaft.

The LM393 detects the slots and produces digital pulses. These pulses are connected to Arduino '''D2'''.

D2 uses an external interrupt to count the pulses.

Every '''1 second''', the Arduino:

# Reads the number of encoder pulses.
# Resets the pulse counter.
# Converts the pulse count into RPM.
# Displays the result on the Serial Monitor.

The RPM calculation is:

<math>
RPM = \frac{Pulses \times 60}{20}
</math>

For example:

<math>
100\ pulses \rightarrow \frac{100 \times 60}{20} = 300\ RPM
</math>

== Arduino Code ==

<syntaxhighlight lang="cpp">
/*
  Encoder disc:
      20 slots

  Encoder location:
      Gearbox OUTPUT shaft

  Therefore:
      20 pulses = 1 output-shaft revolution

  Encoder:
      LM393 DO -> Arduino D2

  Motor driver:
      L293D
      EN1 -> D5
      IN1 -> D7
      IN2 -> D8
*/

#define ENCODER_PIN 2

#define EN1 5
#define IN1 7
#define IN2 8

#define SLOTS_PER_REV 20
#define MIN_PULSE_INTERVAL_US 2000
#define SAMPLE_TIME_MS 1000

volatile unsigned long pulseCount = 0;
volatile unsigned long lastPulseTime = 0;

int motorPWM = 150;

// Encoder interrupt
void encoderISR()
{
  unsigned long currentTime = micros();

  if ((currentTime - lastPulseTime) >= MIN_PULSE_INTERVAL_US)
  {
    pulseCount++;
    lastPulseTime = currentTime;
  }
}

void setup()
{
  Serial.begin(115200);

  pinMode(ENCODER_PIN, INPUT);

  pinMode(EN1, OUTPUT);
  pinMode(IN1, OUTPUT);
  pinMode(IN2, OUTPUT);

  // Motor direction
  digitalWrite(IN1, HIGH);
  digitalWrite(IN2, LOW);

  // Motor speed
  analogWrite(EN1, motorPWM);

  // Encoder interrupt
  attachInterrupt(
    digitalPinToInterrupt(ENCODER_PIN),
    encoderISR,
    RISING
  );

  Serial.println("RPM");
}

void loop()
{
  static unsigned long lastMeasurement = 0;

  unsigned long currentTime = millis();

  if (currentTime - lastMeasurement >= SAMPLE_TIME_MS)
  {
    unsigned long pulses;

    noInterrupts();
    pulses = pulseCount;
    pulseCount = 0;
    interrupts();

    float rpm =
      (pulses * 60.0) /
      (SLOTS_PER_REV * (SAMPLE_TIME_MS / 1000.0));

    Serial.print("Pulses ");
    Serial.print(pulses);

    Serial.print(",RPM ");
    Serial.println(rpm);

    lastMeasurement = currentTime;
  }
}
</syntaxhighlight>

== Observation ==

The Serial Monitor is set to '''115200 baud'''.

Example observations:

{| class="wikitable"
! Pulse Count
! Calculated RPM
|-
| 80
| 240 RPM
|-
| 82
| 246 RPM
|-
| 81
| 243 RPM
|-
| 83
| 249 RPM
|}

Example Serial Monitor output:

<syntaxhighlight>
RPM
Pulses 80,RPM 240.00
Pulses 82,RPM 246.00
Pulses 81,RPM 243.00
Pulses 83,RPM 249.00
</syntaxhighlight>

'''Result:''' The Arduino successfully controls the geared motor and measures the '''gearbox output-shaft RPM''' using the 20-slot LM393 encoder.