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power.md

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layout title permalink sequence power_tree power_source battery_life charging_duration charging_instruction
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Power
/power
6
true
<code>2000mAh</code> LiPo battery
1 month
12 hours
Remove the WeMos Battery shield from the board. Plug in the USB cable to the WeMos battery shield to charge. <code>Red</code> LED will be on while it is charging.<code>Green</code> LED will be on when charging is complete.

Main components

<table class="table is-fullwidth">
  <thead>
    <tr>
      <th>Chip #</th>
      <th>Chip</th>
      <th>Operating Voltage</th>
      <th>Active mode</th>
      <th>Modem-sleep mode</th>
      <th>Deep-sleep mode</th>
      <th>Total</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>ESP8266</td>
      <td>WiFi based MCU</td>
      <td><code>3.3V</code></td>
      <td><code>170mA</code></td>
      <td><code>15mA</code></td>
      <td><code>10uA</code></td>
      <td></td>
    </tr>
    <tr>
      <td>Si7021</td>
      <td>Temperature / Humidity sensor</td>
      <td><code>1.9V</code> - <code>3.6V</code></td>
      <td><code>150uA</code></td>
      <td></td>
      <td><code>60nA</code></td>
      <td></td>
    </tr>
    <tr>
      <td>SN4HC595</td>
      <td>Shift register</td>
      <td><code>2V</code> - <code>6V</code></td>
      <td><code>60uA</code></td>
      <td></td>
      <td><code>1uA</code></td>
      <td></td>
    </tr>
    <tr class="is-selected">
      <td>Total consumption</td>
      <td></td>
      <td></td>
      <td><code>170.23mA</code></td>
      <td><code>15mA</code></td>
      <td><code>11.06uA</code></td>
      <td></td>
    </tr>
    <tr class="is-selected">
      <td>Total duration</td>
      <td></td>
      <td></td>
      <td>30s.</td>
      <td>10s x 12 = 120s.</td>
      <td>4h.</td>
      <td>4h.</td>
    </tr>
    <tr class="is-selected">
      <td>Total charge</td>
      <td></td>
      <td></td>
      <td>30/14400 * 170.21m <br>= 0.354 mAs</td>
      <td>120/14400 *15m <br>= 0.125mAs</td>
      <td>14250/14400 * 11.06u <br>= 0.011mAs</td>
      <td>0.589mAs</td>
    </tr>
  </tbody>
</table>

Calculation

<div class="content is-medium">
  <p>3 power modes:</p>

  <ol>
    <li>Wakes up in <strong>Active mode</strong> for 30 seconds every 4 hours to read the sensor value and ping to cloud</li>
    <li>Wakes up in <strong>Mode-sleep mode</strong> for <strong>10 seconds</strong> every <strong>20 minutes</strong> to check whether the counter has reached the threshold</li>
    <li><strong>Deep-sleep mode</strong> for the rest of the time, unless user button pressed</li>
  </ol>

  <p><code>1200mAh</code> battery will last for <code>(1200/24/30)</code> = <strong>2.89 months</strong></p>
</div>

Measuring power

<table class="table is-fullwidth">
  <thead>
    <tr>
      <td>Mode</td>
      <td>Pins</td>
      <td>Voltage</td>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>Deep sleep</td>
      <td><code>5V</code> - <code>GND</code> on WeMos D1 mini</td>
      <td><code>4.94V</code></td>
    </tr>
    <tr>
      <td>Deep sleep</td>
      <td><code>Vin</code> - <code>GND</code> on Si7021 breakout board</td>
      <td><code>5V</code></td>
    </tr>
    <tr>
      <td>Deep sleep</td>
      <td><code>Vcc</code> - <code>GND</code> on 74HC595 chip</td>
      <td><code>5V</code></td>
    </tr>
    <tr>
      <td>Deep sleep</td>
      <td><code>EN</code> - <code>GND</code> on 74HC595 chip</td>
      <td></td>
    </tr>
  </tbody>
</table>

Actual vs. Calculated

<table class="table is-fullwidth">
  <thead>
    <tr>
      <td>Periodic wakeup</td>
      <td>Calculated</td>
      <td>Actual</td>
      <td>Error %</td>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>6 hours</td>
      <td>2.89 months</td>
      <td>30 days</td>
      <td>~300% ⁉️</td>
    </tr>
  </tbody>
</table>