Trace a timer sleep-and-wake cycle

Trace two sleep-and-wake cycles and audit the measured state ledger behind an average-current and lifetime estimate.

Physics Phoebe: I want you to audit each state duration and measured current before trusting the lifetime number., your practice guide

Physics Phoebe: I want you to audit each state duration and measured current before trusting the lifetime number.
Predict the reading, then compare it with the measurement.

Wokwi ESP32

Third party Tool

Trace two sleep-and-wake cycles and audit the measured state ledger behind an average-current and lifetime estimate.

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

1,262 bytes · Circuit connections

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{
  "version": 1,
  "author": "IoTClass",
  "editor": "wokwi",
  "parts": [
    {
      "type": "wokwi-esp32-devkit-v1",
      "id": "esp",
      "top": 20,
      "left": 0,
      "attrs": {}
    },
    {
      "type": "wokwi-potentiometer",
      "id": "sensor",
      "top": -120,
      "left": 260,
      "attrs": {}
    },
    {
      "type": "wokwi-led",
      "id": "status",
      "top": 170,
      "left": 260,
      "attrs": {
        "color": "green",
        "label": "awake"
      }
    },
    {
      "type": "wokwi-resistor",
      "id": "r1",
      "top": 250,
      "left": 260,
      "attrs": {
        "value": "220"
      }
    }
  ],
  "connections": [
    [
      "esp:TX0",
      "$serialMonitor:RX",
      "",
      []
    ],
    [
      "esp:RX0",
      "$serialMonitor:TX",
      "",
      []
    ],
    [
      "esp:D12",
      "sensor:VCC",
      "red",
      []
    ],
    [
      "esp:D34",
      "sensor:SIG",
      "blue",
      []
    ],
    [
      "esp:GND.1",
      "sensor:GND",
      "black",
      []
    ],
    [
      "esp:D2",
      "status:A",
      "green",
      []
    ],
    [
      "status:C",
      "r1:1",
      "black",
      []
    ],
    [
      "r1:2",
      "esp:GND.1",
      "black",
      []
    ]
  ]
}

sketch.ino

2,058 bytes · ESP32 program

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#include <Arduino.h>
#include <esp_sleep.h>

constexpr uint64_t SLEEP_SECONDS = 5;  // Simulator teaching interval; deployment example is 900 s.
constexpr int SENSOR_ENABLE_PIN = 12;
constexpr int SENSOR_INPUT_PIN = 34;
constexpr int STATUS_LED_PIN = 2;

RTC_DATA_ATTR uint32_t wakeCount = 0;

void preparePeripheralsForSleep() {
  digitalWrite(STATUS_LED_PIN, LOW);
  pinMode(STATUS_LED_PIN, INPUT);
  digitalWrite(SENSOR_ENABLE_PIN, LOW);
  pinMode(SENSOR_ENABLE_PIN, OUTPUT);
}

void printMeasuredLedger() {
  const float chargeMilliampSeconds =
      (0.018f * 895.0f) + (6.0f * 2.0f) + (24.0f * 1.0f) + (110.0f * 2.0f);
  const float averageMilliamps = chargeMilliampSeconds / 900.0f;
  const float usableCapacityMah = 2400.0f * 0.70f;
  const float lifeDays = usableCapacityMah / averageMilliamps / 24.0f;
  Serial.printf("LEDGER charge=%.2f mA*s average=%.3f mA\n",
                chargeMilliampSeconds, averageMilliamps);
  Serial.printf("LIFE usable=%.0f mAh estimate=%.0f days\n",
                usableCapacityMah, lifeDays);
}

void setup() {
  Serial.begin(115200);
  delay(100);

esp_sleep_wakeup_cause_t cause = esp_sleep_get_wakeup_cause();
  if (cause == ESP_SLEEP_WAKEUP_UNDEFINED) wakeCount = 0;
  wakeCount++;

pinMode(STATUS_LED_PIN, OUTPUT);
  pinMode(SENSOR_ENABLE_PIN, OUTPUT);
  digitalWrite(STATUS_LED_PIN, HIGH);
  digitalWrite(SENSOR_ENABLE_PIN, HIGH);

Serial.printf("ENERGY CYCLE wake=%lu cause=%d\n",
                (unsigned long)wakeCount, static_cast<int>(cause));
  delay(250);
  int reading = analogRead(SENSOR_INPUT_PIN);
  Serial.printf("STATE sensor-warmup duration=250 ms reading=%d\n", reading);
  Serial.println("STATE active-compute status=ON sensor=ON");
  printMeasuredLedger();

preparePeripheralsForSleep();
  Serial.printf("SLEEP timer=%llu s status=OFF sensor=OFF\n",
                (unsigned long long)SLEEP_SECONDS);
  Serial.flush();

esp_sleep_enable_timer_wakeup(SLEEP_SECONDS * 1000000ULL);
  esp_deep_sleep_start();
}

void loop() {
  // Execution restarts in setup() after deep sleep.
}

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 and trace the switched sensor and status paths.
You will see
GPIO12 powers the simulated sensor, GPIO34 reads its signal, and GPIO2 drives the awake-status LED.
Why it matters
A whole-node energy trace must include sensor and status loads rather than measuring only the microcontroller.
Step 2
Do
Inspect the wake counter, wake-cause check, and five-second teaching interval.
You will see
wakeCount uses RTC_DATA_ATTR, undefined startup resets the count, and the timer interval is explicitly labeled as a simulator acceleration.
Why it matters
Retained state and wake cause make consecutive duty-cycle traces distinguishable and reproducible.
Step 3
Do
Start the simulation and open Serial Monitor at 115200 baud.
You will see
ENERGY CYCLE wake=1 cause=0 appears for the initial boot.
Why it matters
The first cycle establishes the baseline reset reason before any timer wake is interpreted.
Step 4
Do
Inspect the first cycle's state lines.
You will see
The sensor warm-up lasts 250 ms, then active-compute reports status=ON and sensor=ON.
Why it matters
Separating warm-up and active work prevents a short high-current state from disappearing inside an average.
Step 5
Do
Read the measured ledger calculation and compare its two summary lines.
You will see
The source chapter's example prints 272.11 mA*s, 0.302 mA average, 1680 mAh usable capacity, and about 232 days.
Why it matters
A calculator result becomes reviewable only when its state currents, durations, capacity reserve, and arithmetic remain visible.
Step 6
Do
Confirm the pre-sleep line before the board sleeps.
You will see
SLEEP timer=5 s status=OFF sensor=OFF appears after the status and sensor pins are shut down.
Why it matters
The simulator can prove control state and timing, but not the physical board's true sleep current.
Step 7
Do
Wait at least 6.5 seconds for a second timer cycle; if the web editor does not resume after deep sleep, record that limitation.
You will see
In this captured web run, the last application line remains SLEEP timer=5 s status=OFF sensor=OFF; no second ENERGY CYCLE line appears.
Why it matters
The missing web-editor wake is evidence of a simulator boundary, so timer-wake retention still requires a physical-board trace before a power policy is accepted.

Chapter checks

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

A battery-life calculator predicts four years, but the model uses datasheet sleep current, nominal battery capacity, and one successful radio transmission per cycle. What should the engineer do before accepting the result?
Return to the chapter’s knowledge check
Beyond a single lifetime figure, what is the most useful thing a battery-life tool provides?
Return to the chapter’s knowledge check
For a node that reports once per hour with a 0.5 s active burst, a sweep shows halving sleep current gives +59% life while halving active current gives +15%. Which optimization should the team pursue first, and why?
Return to the chapter’s knowledge check

Return to Power Management Tools · 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