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

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

Download

{
  "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

Download

#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
In Wokwi's project editor, paste diagram.json and sketch.ino into a new Wokwi ESP32 project and trace the switched sensor and status paths.
You will see
ESP32 GPIO12 supplies the sensor VCC path (diagram.json line 54). Sensor signal connects to ESP32 GPIO34 (diagram.json line 60). Sensor ground connects to ESP32 ground (diagram.json line 66). Status LED anode connects to ESP32 GPIO2; its cathode returns through r1 to ground (diagram.json lines 72, 78, 84). The status LED’s resistor r1 is 220 Ω (diagram.json line 32).
Why it matters
GPIO12 switches the simulated sensor supply before a sample, GPIO34 reads it, and GPIO2 marks the awake phase. Those separate paths make later sleep-cycle output interpretable.
Step 2
Do
In Wokwi's sketch editor, inspect the wake counter, wake-cause check, and five-second teaching interval.
You will see
Set the simulator sleep interval: constexpr uint64_t SLEEP_SECONDS = 5; // Simulator teaching interval; deployment example is 900 s. (sketch.ino line 4). Name sensor-enable GPIO12: constexpr int SENSOR_ENABLE_PIN = 12; (sketch.ino line 5). Name sensor-input GPIO34: constexpr int SENSOR_INPUT_PIN = 34; (sketch.ino line 6). Name status-LED GPIO2: constexpr int STATUS_LED_PIN = 2; (sketch.ino line 7). Keep a wake counter across sleep: RTC_DATA_ATTR uint32_t wakeCount = 0; (sketch.ino line 9).
Why it matters
The five-second constant is the simulator teaching interval. Pin constants identify the switched sensor and status paths, while RTC_DATA_ATTR preserves the wake counter across later sleep cycles.
Step 3
Do
In the Simulation toolbar, start the run and read the first Serial Monitor heading.
You will see
Input: start the supplied timer-sleep sketch. Observed: "ENERGY CYCLE wake=1 cause=0". Observed: the heading appears before sensor warm-up. Expected: one initial boot with wake counter 1.
Why it matters
The wake counter begins at one. The reported wake cause is zero. This is the first run through setup. The later sleep line must be read separately.
Step 4
Do
In the Serial Monitor panel, inspect the warm-up and active-compute rows.
You will see
Input: leave the first cycle running. Observed: "STATE sensor-warmup duration=250 ms reading=0". Observed: "STATE active-compute status=ON sensor=ON". Expected: sensor warm-up precedes active computation.
Why it matters
The warm-up duration is 250 ms in this model. The warm-up reading is zero. Both status and sensor are ON for active computation. The ordering is visible in the live serial trace.
Step 5
Do
In the Serial Monitor panel, read the charge ledger and life estimate.
You will see
Input: inspect the first cycle summary. Observed: "LEDGER charge=272.11 mA*s average=0.302 mA". Observed: "LIFE usable=1680 mAh estimate=232 days". Expected: the average and estimate follow the simulated ledger.
Why it matters
The model reports 272.11 mA*s per cycle. It reports 0.302 mA average. The usable capacity is 1680 mAh. The 232-day figure is an estimate from this teaching model.
Step 6
Do
In the Serial Monitor panel, confirm the pre-sleep line.
You will see
Input: observe the end of the first cycle. Observed: "SLEEP timer=5 s status=OFF sensor=OFF". Observed: the status and sensor had been ON during active-compute. Expected: both switched paths turn OFF before sleep.
Why it matters
The timer is set for five seconds. Both switched paths report OFF. This is the last application line before deep sleep. It shows a state transition, not measured battery life.
Step 7
Do
In the Serial Monitor panel, wait past the five-second timer and look for a second heading.
You will see
Input: wait until the Wokwi clock reaches 8.866 s. Observed: the last application line remains "SLEEP timer=5 s status=OFF sensor=OFF". Observed: no second "ENERGY CYCLE" line appeared. Expected: record this web-simulator limitation.
Why it matters
The first cycle completed. The monitor did not show another wake heading by 8.866 s. A missing second heading cannot prove that physical hardware would stay asleep. This matches the real captured web-editor limit.

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