Build an LDR change-evidence record

Collect a bounded before-change-after-retest LDR record that preserves sensor identity, sample order, units, validity, setup changes, and claim limits.

Physics Phoebe: I want you to preserve the question, state change, units, validity, and retest trigger—not just the number., your practice guide

Physics Phoebe: I want you to preserve the question, state change, units, validity, and retest trigger—not just the number.
Predict the reading, then compare it with the measurement.

Wokwi ESP32

Third party Tool

Collect a bounded before-change-after-retest LDR record that preserves sensor identity, sample order, units, validity, setup changes, and claim limits.

Tier 1 · Web · No account

Version tested: Compiled and booted by the Wokwi gate (ESP32 Arduino core 3.3.11); captured in the Wokwi web editor on 2026-09-09. Date: 2026-09-09.

Open the ESP32 editor, paste diagram.json, then paste sketch.ino.

Open Wokwi to paste in the files (new tab)

Get the files

Use both prepared files. This is a paste-in setup; saving a project requires a Wokwi account.

diagram.json

558 bytes · Circuit connections

Download

sketch.ino

1,009 bytes · ESP32 program

Download

constexpr uint8_t LDR_PIN = 34;
uint32_t sampleNumber = 0;
char condition[16] = "STARTUP";

void readConditionCommand() {
  if (!Serial.available()) return;
  String label = Serial.readStringUntil('\n');
  label.trim();
  if (label.length() > 0 && label.length() < sizeof(condition)) {
    label.toUpperCase();
    label.toCharArray(condition, sizeof(condition));
    Serial.printf("CHANGE note=%s retest-required=yes\n", condition);
  }
}

void setup() {
  Serial.begin(115200);
  analogReadResolution(12);
  Serial.println("LDR LAB scope=direction-only reference=none");
  Serial.println("QUESTION does-light-change-move-the-recorded-signal");
}

void loop() {
  readConditionCommand();
  const int raw = analogRead(LDR_PIN);
  const float voltage = raw * 3.3f / 4095.0f;
  const bool valid = raw >= 0 && raw <= 4095;
  sampleNumber++;
  Serial.printf("EVIDENCE n=%lu id=ldr state=%s raw=%dcount V=%.3f valid=%c\n",
                sampleNumber, condition, raw, voltage, valid ? 'Y' : 'N');
  delay(500);
}

Use the launch button above to open the ESP32 editor in Wokwi.
Select the editor’s diagram.json tab and replace all its text with the supplied diagram.json.
Select the sketch.ino tab, replace all its text with the supplied sketch.ino, then click Start Simulation.

Steps

Screens captured against Wokwi ESP32 Compiled and booted by the Wokwi gate (ESP32 Arduino core 3.3.11); captured in the Wokwi web editor on 2026-09-09 on 2026-09-09; the tool may have moved on — the text steps are the contract.

Step 1
Do
Paste diagram.json and sketch.ino into a new Wokwi ESP32 project, then trace the LDR module's analog path.
You will see
The module uses 3.3 V and common ground, with analog output connected to GPIO34.
Why it matters
The controller, sensor identity, supply, and signal path are setup evidence for every later reading.
Step 2
Do
Inspect the serial change-note handler and evidence-record output.
You will see
Each record preserves sample order, LDR identity, named setup state, ADC counts, voltage, and validity.
Why it matters
A value without identity, units, context, and validity cannot support a reviewable interpretation.
Step 3
Do
Start the simulation and read the declared scope and measurement question.
You will see
The lab declares direction-only scope, no reference, and asks whether a light change moves the recorded signal.
Why it matters
The declaration prevents simulated ADC values from being mistaken for calibrated lux or building-performance evidence.
Step 4
Do
Send BASE in Serial Monitor while the supplied LDR control remains at 500 lux.
You will see
The next valid record pairs a BASE state with an ADC count and derived voltage.
Why it matters
A named starting condition gives the later direction-of-change result a comparison point.
Step 5
Do
Set the LDR control to 50 lux, send SHADE, and preserve the next reading.
You will see
The SHADE evidence record changes from the baseline while retaining identity, count units, voltage, and valid state.
Why it matters
The before-and-after pair supports only the direction-of-change claim in this simulated setup.
Step 6
Do
Set the LDR control to 10,000 lux, send BRIGHT, and preserve the next reading.
You will see
The BRIGHT record moves in the opposite direction from SHADE and remains within the 12-bit ADC range.
Why it matters
Exercising both sides of the baseline is stronger evidence than one attractive reading.
Step 7
Do
Restore the LDR control to 500 lux, send RETEST, and compare with the baseline.
You will see
The RETEST record returns near the original simulated baseline value.
Why it matters
A return test checks repeatability and states the trigger: any placement, optical cover, wiring, sampling, or reference change requires a new record.

Chapter checks

These questions refer to the chapter’s examples. Use the return links to review their answers.

A team chooses a sensor module because it is easy to wire, but the review does not state placement, calibration, environment, or the decision it supports. What is the strongest finding?
Return to the chapter’s knowledge check
A soil-moisture sensor works during a classroom demo but degrades after outdoor installation. What should the practitioner add to the hardware decision record?
Return to the chapter’s knowledge check
A room comfort sensor is mounted inside a sealed electronics box, and its readings track board heat more than room air. What is the best under-the-hood response?
Return to the chapter’s knowledge check

Return to Sensor Hardware Selection · Browse Labs

Wokwi ESP32

Get the files

diagram.json

sketch.ino

Steps

1 Step 1

2 Step 2

3 Step 3

4 Step 4

5 Step 5

6 Step 6

7 Step 7

Chapter checks

Step 1

Step 2

Step 3

Step 4

Step 5

Step 6

Step 7