HKD Slotted Optical Speed Sensor Module — 74HC14 Schmitt Trigger, TTL Output for Arduino & ESP32

Handy Tips

1. Works with encoder / code wheels — Mount this sensor around a slotted encoder disc (code wheel) on a motor shaft or wheel axle. Each slot that passes through the beam generates one pulse on the output pin. Count pulses per second and divide by the number of slots on your disc to calculate RPM or surface speed accurately.
2. Schmitt trigger gives clean, stable pulses — The onboard 74HC14 Schmitt trigger cleans up the raw phototransistor signal, eliminating the slow rise/fall edges and bounce that raw optical sensors produce. This makes it safe to connect directly to a microcontroller interrupt pin without additional filtering or debounce circuitry.
3. Use hardware interrupts for accurate counting — Attach the output pin to a hardware interrupt-capable GPIO and count pulses in an ISR (Interrupt Service Routine). At higher RPMs the pulse rate can exceed what polling in a main loop can reliably capture — missed pulses directly translate to underreported speed readings.
4. Output is active LOW — The output goes LOW when an opaque object interrupts the IR beam and returns HIGH when the beam is clear. In speed measurement applications this means each falling edge represents one slot passing through the sensor — trigger your interrupt on FALLING for the most consistent timing reference.
5. Slot width limits maximum disc tooth size — The 5.9mm slot accommodates encoder disc teeth and flags up to approximately 5mm wide. Ensure your code wheel teeth are narrow enough to pass cleanly through the slot without touching the sensor body — physical contact will damage the sensor and produce erratic output.
6. Transparent or translucent objects will not trigger — The sensor only triggers when the IR beam is fully interrupted by an opaque object. Clear acrylic, thin paper, and semi-transparent plastics may pass through the slot without reliably breaking the beam. Use a solid opaque encoder disc material such as black PLA, ABS, or metal for consistent triggering.
7. M3 mounting holes allow precise alignment — Use both M3 mounting holes to secure the sensor rigidly to your chassis or bracket. Any flex or vibration in the sensor mounting will cause the encoder disc to drift within the slot, introducing timing jitter and inconsistent pulse widths that degrade speed measurement accuracy.