Contactless Digital Tachometer using IR Sensor

Measuring rotational speed without touching the shaft matters wherever contact would disturb the measurement or wear the sensor — motors, turbines, spindles. The industrial answer is non-contact sensing: a reflective mark on the shaft, an optical sensor watching it, and a counter converting pulses per second into RPM. This project implements exactly that with student hardware: an IR reflective sensor module faces a motor shaft carrying a contrasting mark, each pass generates a pulse, and the Arduino counts pulses over a one-second gate (or measures pulse period) to compute revolutions per minute on a 16x2 LCD. Hold and averaging modes, a low/high range, and a calibration procedure against a known reference make it a complete measurement-instrument build rather than a toy counter.

1. A contrasting (white) mark is fixed on the motor shaft; the IR sensor module is positioned a few millimetres away, facing it.
2. Each shaft revolution carries the mark past the sensor once, producing a clean digital pulse via the module's comparator.
3. The pulse feeds an Arduino external-interrupt pin, which increments a counter on every rising edge.
4. Once per second (the gate time), firmware reads the counter, computes RPM as pulses-per-second × 60 ÷ marks-per-revolution, and resets the counter.
5. The result is written to the 16x2 LCD; in average mode the firmware smooths several consecutive gate readings.
6. The hold button freezes the displayed value; the range/marks button cycles the marks-per-revolution setting.

Tech stack:

• Arduino Uno (ATmega328P)
• IR reflective sensor module (with comparator)
• 16x2 character LCD
• DC demo motor with marked shaft disc
• Push buttons (hold, mode)
• 5–9 V power supply
• Arduino IDE (C/C++ firmware)

• [Non-contact IR sensing] A reflective IR sensor detects a contrasting mark on the rotating shaft — nothing touches the shaft, so the measurement adds no load.
• [Interrupt-driven counting] Shaft pulses are captured on a hardware interrupt for accurate counting even at high RPM, independent of LCD update timing.
• [Live RPM on 16x2 LCD] Revolutions per minute update continuously on the character LCD with a stable, readable refresh rate.
• [Hold and average modes] A push button freezes the reading (hold); a second mode averages over multiple gates to smooth fluctuating speeds.
• [Marks-per-revolution setting] Firmware supports 1 or multiple marks per revolution, configurable for different shaft setups.
• [Demo motor included] A DC motor with a marked disc is part of the kit, so the instrument is demonstrated end to end out of the box.
• [Calibration procedure] The report includes a buyer-run procedure to verify readings against a reference (e.g. a second instrument or a known supply frequency).

• IR sensor head with mounting stand
• Demo DC motor with marked shaft disc
• Arduino Uno with tachometer firmware
• 16x2 LCD and control buttons
• Calibration and operating procedure
• Project report PDF (optical sensing, interrupts, RPM computation, calibration)
• PPT presentation for final review
• Viva Q&A preparation document

• Needs a contrasting mark on the shaft and a stable few-mm standoff; dark, tiny or inaccessible shafts need preparation by the user.
• The ±1% figure is a design target verified by the buyer's own calibration — the report documents the procedure rather than claiming a measured result.
• Very low RPM (below ~30) needs a longer gate time for resolution; the firmware documents this tradeoff.
• Ambient IR (direct sunlight on the sensor) can disturb readings; indoor demo lighting is recommended.
• It measures speed only — torque, vibration and direction need separate instruments.