MOC7811 - Encoder Sensor

Specifications

• Sensor Type: Slotted Optical Switch / Photointerrupter
• Sensing Technology: Infrared (IR) Emitter & Phototransistor Receiver
• Gap Width: Standard ~3mm to 5mm slot (Perfect for acrylic or PCB encoder disks)
• Output: Analog (Requires an external comparator or ADC for clean digital logic)
• Operating Voltage: 3.3V to 5V (Typical for IR LED and Receiver circuits)
• Package Style: Compact black plastic housing to block ambient light interference
• Mounting: Features two built-in mounting holes on the body for easy chassis integration

Applications

• Robotics & Odometry: Build custom wheel encoders to track exactly how far your autonomous rover has traveled.
• Motor Speed Control: Monitor the RPM of DC gear motors to implement precise PID control loops.
• Industrial Automation: Use as a non-contact limit switch or object counter on small conveyor belts.
• 3D Printers & CNC: Highly repeatable end-stop detection for linear rails and mechanical axes.
• DIY Tachometers: Accurately measure the rotational speed of cooling fans, spindles, or any rotating shaft.

Unlock New Capabilities

• Past Projects: If you've mastered basic obstacle avoidance using generic IR modules, you know they can be sensitive to ambient light and reflection angles.
• The Upgrade: The MOC7811 unlocks closed-loop control. Instead of just telling a motor to "go forward," this sensor allows your microcontroller to verify that the motor is actually turning at the requested speed.

Package Includes:

• 1 x MOC7811 - Encoder Sensor

Frequently Asked Questions (FAQ)

• What is the MOC7811 sensor used for?
  It is used to detect the presence of an object passing through its slot, commonly used with slotted disks to measure motor speed (RPM) or position.
• Does the MOC7811 output a digital or analog signal?
  The raw MOC7811 outputs an analog signal based on the amount of light hitting the phototransistor. You need external resistors or a comparator to convert it to a clean digital pulse.
• Can I connect the MOC7811 directly to an Arduino?
  Yes, but you MUST use a current-limiting resistor for the internal IR LED and a pull-up resistor for the phototransistor output.
• What voltage does the MOC7811 require?
  The internal IR LED typically drops around 1.2V to 1.5V, but the system is usually powered from a 3.3V or 5V source using the appropriate resistors.
• How do I calculate motor RPM using this sensor?
  Count the number of pulses in a specific time frame using an interrupt, then divide by the number of slots on your encoder disk, and multiply by 60 to get RPM.
• Why is my microcontroller missing pulses at high speeds?
  You likely need a comparator circuit (like an LM393) to square up the analog waveform into a sharp digital signal, or you need to use hardware interrupts instead of polling the pin.
• Is the MOC7811 affected by sunlight?
  While the black plastic housing blocks most ambient light, intense direct sunlight hitting the gap can sometimes cause false readings.
• What is the gap width of the MOC7811?
  The gap is wide enough to comfortably fit standard 3mm acrylic or PCB-based rotary encoder disks.
• Can it detect the direction of rotation?
  A single MOC7811 can only detect speed (pulses). To detect direction, you need two sensors positioned in a quadrature arrangement.
• What resistor value should I use for the IR LED?
  For a 5V supply, a 220Ω or 330Ω resistor is standard to limit the forward current to a safe operating level.
• What resistor value should I use for the phototransistor?
  A 10kΩ pull-up resistor on the collector pin is standard for interfacing with microcontroller logic.