Students will
- Identify the phototransistor collector and emitter before wiring
- Read and describe an analog light-sensing signal
- Choose and test a threshold between two measured conditions
Arduino Uno R3
Light to threshold
Measure the kit phototransistor circuit, collect evidence, calibrate a threshold, and publish a dependable light event.
MS-DAT-DC-21Data & AnalysisMS-DAT-DI-27Data & Analysis
Evidence of success
- A table of repeated readings in two conditions
- A threshold justified from measured values
- Ten repeated trials with false triggers identified
Hardware
- Arduino Uno R3
- Starter Kit phototransistor
- 10 kΩ resistor
- Breadboard and jumper wires
- Small light source
Prerequisites
- Upload a sketch
- Open Serial Monitor
- Identify 5V, GND, and A0
Before class
- Verify the actual phototransistor identity, polarity, and reviewed Starter Kit circuit
- Confirm the 10 kΩ resistor value and breadboard rows
- Provide stable bright and shaded test conditions
Reviewed connection map
Phototransistor sensing divider
- Build the reviewed Starter Kit phototransistor and 10 kΩ resistor circuit with power disconnected.
- Connect the divider junction to A0.
- Verify sensor orientation, 5V, and GND before connecting USB.
Build and test
- 01Identify the phototransistor collector and emitter from the reviewed part information
- 02With power disconnected, build the reviewed phototransistor and 10 kΩ resistor circuit with A0 at the signal junction
- 03Print analogRead(A0) once every 100 ms and observe whether readings rise or fall with light
- 04Record repeated shaded and illuminated readings, then choose a threshold between the observed ranges
- 05Test near the boundary and revise if false triggers occur
Read before uploading
Annotated Arduino sketch
const int SENSOR_PIN = A0;
int threshold = 500;
void setup() {
Serial.begin(9600);
}
void loop() {
int reading = analogRead(SENSOR_PIN);
bool lightEvent = reading > threshold;
Serial.print(reading);
Serial.print(" event=");
Serial.println(lightEvent);
delay(100);
}Optional engineering record
Record evidence from this lesson
Choose the prompts that help students explain predictions, evidence, debugging, and transfer. Saving creates a new entry in this browser’s Rudi notebook.
Record your thinking — optional4 prompts
Use these prompts if they help students capture evidence, decisions, or questions. You do not need to complete every prompt or create an entry at every step.
Nothing is saved until you choose this button.
Troubleshooting
Reading stays near 0 or 1023
Disconnect power, then verify the phototransistor polarity, A0 signal junction, resistor value, 5V, and GND.
Light makes the reading move in the opposite direction
Use the observed direction in the comparison rather than assuming that brighter must produce a larger value.
Trigger changes with room light
Recalibrate in the actual installation and shield the sensor where appropriate.
2026 middle school standards
Potential CSTA connections
These are evidence-based crosswalk candidates for curriculum review—not a claim of official alignment.
Evaluate how different levels of precision and granularity in data collection affect accuracy, storage, and analysis.
Students compare repeated analog measurements and choose a useful level of precision for a threshold.
Lesson evidence: Bright and shaded reading tableSummarize a data investigation process, including potential biases, limitations, and supporting evidence.
Students collect repeated sensor readings, identify limitations, and support a threshold or response with evidence.
Lesson evidence: Threshold justification and ten-trial testSupporting concepts
component-boards · power-and-signals · ohms-law
Sources and review
Arduino Uno R3 documentationArduino Projects Book · CC BY-NC-SA 3.0Starting point, not verified curriculum. Review the actual hardware, circuit, code, power requirements, and classroom conditions.
After teaching this lesson