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layout title permalink sequence power
power
Power
/power
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tree components calculation source battery_life charging_duration charging_instruction
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<code>1500mAh</code> Rechargeable 16320 battery
1.12 year
??? hours
Plug in a USB-C cable to charge the battery.

Power consumption

Using nRF Power Profiler PPk2, the power consumption of the PCB can be measured. Follow a simpler ESP32-C3 dev board tutorial to learn how to use PPK2.

![Measure power consumption with nRF PPK2]({{ site.url }}/images/power/measure-power-ppk2.jpg)

Power consumption with no optimisation

The average power consumption of the PCB no optimisation:

  • with 2 power LEDs
  • no firmware optimisation
  • radio is on

The average power consumption is:

  • 3.87mA in deep sleep mode
  • 25.69mA for 30s during the timeout after the bell is pressed and the Ding Dong sound is played
  • 31.94mA for 34s during the entire cycle of the bell press and going to sleep
  • 70.62mA for 6s during the Ding Dong sound

Download nRF PPK2 file

[![Demo power consumption graph with no optimisation]({{ site.url }}/images/power/demo-power-consumption-no-optimisation.jpg)]({{ site.url }}/images/power/demo-power-consumption-no-optimisation.jpg)

Power consumption with optimisation

Firmware and hardware optimisation can be done to reduce the power consumption:

  • remove the power LEDs, TX and RX LEDs
  • optimise the firmware to turn off the WiFi and radio as soon as the function is done: WiFi.disconnect(true); and WiFi.mode(WIFI_OFF);
  • optimise the firmware to not blink the user LED

The average power consumption of the PCB with optimisation:

  • 73.04uA in deep sleep mode
  • 17.11mA for 30s during the timeout after the bell is pressed and the Ding Dong sound is played
  • 24.93mA for 34s during the entire cycle of the bell press and going to sleep
  • 63.99mA for 6s during the Ding Dong sound

Download nRF PPK2 file with no LED

Download nRF PPK2 file with no LED and radio/WiFi [![Demo power consumption graph with optimisation]({{ site.url }}/images/power/demo-power-consumption-optimised.jpg)]({{ site.url }}/images/power/demo-power-consumption-optimised.jpg)

Battery life calculation

Based on the above values, the battery life can be calculated with this python code:

Estimated battery life: 410.14 days or 1.12 years

{% highlight python %} {% include_relative power/calc_battery_life.py %} {% endhighlight %}

Battery measurement simulation

The battery measurement circuit is simulated in Falstad.

$ 1 0.000005 5.023272298708815 78 5 50 5e-11
172 224 240 176 240 0 7 0 3.3 0 0 0.5 Gate Voltage
w 352 224 352 176 1
f 288 240 352 240 33 1.5 0.02
R 352 176 352 144 0 0 40 4.2 0 0 0.5
c 224 240 288 240 0 0.1 0.000999999998577626 0.001
r 288 192 336 192 0 1000000
w 336 192 352 192 0
w 288 192 288 240 0
g 352 352 352 368 0 0
r 352 256 352 304 0 100000
r 352 304 352 352 0 100000
w 352 304 256 304 0
o 2 64 0 4099 0.001220703125 0.00009765625 0 2 2 3

With a p-channel MOSFET, when the gate voltage is 0V or LOW, the battery voltage is measured. When the gate voltage is 3.3V or HIGH, the battery voltage cannot be measured.

Charging setup

The battery is charged with a USB-C cable. Plug in the USB-C cable to a power socket on-the-wall or a power bank.

[![Charging on-site]({{ site.url }}/images/power/charging-onsite.jpeg)]({{ site.url }}/images/power/charging-onsite.jpeg)