Arduino Frequency Counter

Bench frequency measurement is one of the most common lab tasks in electronics — oscillators, function generators, PWM outputs and clock sources all need their frequency verified, yet many college labs have only one or two commercial counters to share. This project shows the student building the instrument themselves: an Arduino Uno counts input pulses with its hardware timer, so the firmware stays simple and the counting is exact. Because real-world signals are rarely clean logic levels, an LM358 comparator stage with a threshold potentiometer converts sine, triangle or noisy waveforms into clean edges, and a diode clamp protects the Arduino input. The result is shown on a 16x2 LCD, auto-ranged in Hz, kHz and MHz. The build covers embedded timers, interrupts, analog conditioning and measurement error — exactly the mix examiners probe in an electronics viva.

1. The test signal enters the LM358 comparator stage, where the threshold potentiometer sets the trigger level and the output becomes a clean 0–5 V square wave.
2. The squared signal drives the Arduino's external clock input (Timer1 T1 pin), so every rising edge is counted by hardware with no firmware overhead.
3. The firmware opens a fixed 1 s (or 0.1 s) gate, reads the timer count at the end, and converts it to frequency.
4. Below roughly 100 Hz the firmware switches to period mode, timing the interval between successive edges for a more accurate low-frequency reading.
5. The measured value is auto-ranged into Hz, kHz or MHz and shown on the 16x2 LCD alongside the raw pulse count.
6. The student calibrates the unit against a known reference frequency, records the deviation, and reports it honestly in the project documentation.

Tech stack:

• Arduino Uno (ATmega328P)
• LM358 dual op-amp comparator stage
• 16x2 character LCD (HD44780)
• Arduino IDE (C/C++ firmware)
• Breadboard/perfboard assembly
• 5 V USB supply

• [Timer-interrupt pulse counting] The ATmega328P's Timer1 counts input pulses in hardware over a fixed gate time, so no pulse is missed between firmware cycles — the core measurement is handled by silicon, not polling.
• [LM358 input conditioning] A comparator stage with an adjustable threshold squares up sine, triangle and noisy signals into clean logic edges, with a diode clamp protecting the Arduino's 5 V input.
• [Auto-ranging LCD readout] Frequency and raw count appear on a 16x2 LCD, automatically displayed in Hz, kHz or MHz so the student reads the value without mental arithmetic.
• [Selectable gate time] The 1 s gate gives 1 Hz resolution; a faster 0.1 s gate trades resolution for a quicker update — the tradeoff is documented and demonstrated.
• [Low-frequency period mode] Below roughly 100 Hz the firmware measures the time between edges instead of counting pulses, keeping low-frequency readings accurate where gate counting would be slow.
• [Input protection] Diode clamping and a series resistor keep the Arduino input within 0–5 V even if the source is overdriven — a real-world design habit.
• [Buyer-run calibration] A step-by-step procedure compares the counter against a known reference (a function generator or the Arduino's own tone output) so the student documents accuracy on their own build.

• Working Arduino frequency counter prototype
• Arduino firmware source with commented timer/interrupt code
• Schematic and wiring documentation
• Input-conditioning and calibration procedure manual
• Project report PDF (timers, interrupts, conditioning theory, methodology)
• PPT presentation for final review
• Viva Q&A preparation document

• The ~2 MHz upper range is a design target — interrupt latency and the ATmega328P digital input set the practical ceiling; no measured maximum is claimed.
• Inputs must be brought into the conditioning stage's usable amplitude range; very large or very small signals read unreliably.
• Resolution is 1 Hz at the 1 s gate — faster gates trade resolution for speed.
• Accuracy depends on the Arduino's resonator clock; readings are meaningful only after the buyer-run calibration against a reference.
• It counts edges — it does not measure amplitude, duty detail or distortion.
• Single channel only; no simultaneous multi-channel measurement.