Optical Speed Lab Kit

Classes 9-10, typical ages 14–16. Age ranges vary by learner. Guided low-voltage electronics.

Activity engagement

75–105 minutes. Explore 15–20 min · Build 25–35 min · Test and discuss 35–50 min. Estimated time for building, testing and discussion.

What you need

A computer with a USB port and Arduino IDE is required and is not included.

Included components

• Small Breadboard / Mini Solderless Board - 400 points — 1 breadboard
• Jumper Wire Combo - Male to Male, Male to Female and Female to Female Breadboard Connecting Wires (10 Qty Each) — 1 set
• Illustrated Activity Guide and Observation Sheets — 1 set
• Fitted Headers and Labelled Connection Leads — 1 set
• Arduino Uno R3 CH340G version compatible Arduino Development Board — 1 controller board
• USB A to B Programming Cable for Arduino Uno/ Arduino Mega — 1 data cable
• LM393 Motor Speed Measuring Sensor Module — 1 sensor module
• Twenty-Slot Encoder Disc and Hand-Turned Spindle Stand — 1 set

What you learn

• An optical interrupter converts slots into pulses.
• RPM depends on pulses per revolution and measurement time.
• Short measurement windows trade smoothness for responsiveness.

Connection guide

• LM393 optical slot sensor VCC → 5 V; GND → GND; DO → Uno D2.
• Mount the supplied twenty-slot disc so it passes through the sensor gap without touching it. Use the hand spindle only.

Steps to make it

1. Disconnect all power and identify the supplied part labels and pinouts before wiring.
2. Assemble the stable spindle mount and count the disc slots before entering slotsPerTurn.
3. Wire the sensor, upload and turn the disc slowly by hand.
4. Compare one-turn and five-turn pulse totals at slow speed.
5. Turn steadily and compare RPM estimates using one-second and two-second windows.
6. Change only the named parameter for the extension, repeat the controlled trials, save observations and disconnect power afterward.

Programming resources

Arduino IDE: select Arduino Uno and the USB port. Use the supplied USB data cable. Serial Monitor/Plotter: 115200 baud.

Uses the selected board core libraries.

Download starter sketch

Test challenge

Check pulses per full revolution before trusting the displayed RPM.

Observation task

Slot count, measurement window, pulses and computed RPM.

Expected result

Pulses are counted on one edge; RPM = pulses × 60 / (slots × elapsed seconds).

If it does not work

Check sensor gap alignment and the actual disc slot count. Do not spin it with a drill or motor.

Try next

Estimate the minimum resolvable RPM increment for each window length.

Use and supervision

Use only the supplied low-voltage DC parts. Disconnect power before rewiring; check polarity and labelled pinouts. No soldering or exposed mains connections. Adult guidance is recommended.

How this experiment works

Download class activity guide

Cover illustrations show component types. Functional animations explain principles and are not recorded prototype tests. Follow the supplied connection labels and pinouts.