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Battery Monitoring

Summary:

  1. I made my first voltage divider. You need two resistors. I landed on 2 x 300kΩ
  2. Wire them like below. I think it’s right. (Edit, Its not quite right as battery power should go to esp battery terminal) wanted to keep the diagram simple and didn’t want to draw up my full wiring yet. You just add extra wires for power and ground as you need for your other devices. Edit: best to see the wiring diagram now.

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image616Ă—529 64 KB

Longer version and resources:

  1. Article: ESP8266 battery level meter | ezContents blog 37,
  2. Thread: ESPHome Battery Level Sensor 48,
  3. Some help/checks from @ssieb over on Discord ,

From what I could understand the sum of the resistors should be high and the divided voltage should be < 2.4V
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Which led me to my 2 x 300kΩ selection. I also like this “symmetric” design. Doesn’t matter which way you wire it.

Battery sensor snippet

#Notes:
#Voltage divider: Used 2 x 300K Ohm resistors
  - platform: adc
    id: batt_voltage
    name: Battery Voltage
    internal: true
    pin: ${batt_voltage_pin} #ADC1
    update_interval: never
    accuracy_decimals: 2
    attenuation: auto
    filters:
      # #Scale it back up from voltage divided value 2 x 300K > 2.1. 4.2/2.1 = 2.
      - multiply: 2
    on_raw_value:
      then:
      #Sensor update counter.
        - lambda: id(count_batt_voltage).publish_state(id(count_batt_voltage).state +1);
      
#Intermediate sensor. Might consolidate them later.
  - platform: copy
    source_id: batt_voltage
    id: batt_voltage_filtered
    icon: "mdi:battery"
    internal: false
    name:  Battery Voltage
    unit_of_measurement: V
    accuracy_decimals: 2
    filters:
      - median: #Use moving median to smooth noise.
          window_size: 10
          send_every: 10
          send_first_at: 10
       
#Convert the Voltage to a battery  level (%)
  - platform: copy
    source_id: batt_voltage_filtered
    id: batt_level
    internal: false 
    icon: "mdi:battery"
    name: Battery Percent
    unit_of_measurement: '%'
    accuracy_decimals: 0
    filters:
      # Map from voltage to Battery level
      - calibrate_linear:
          - 3.1 -> 0 #Set 3.0 to 0% even though it can go lower (2.4V), for life extention. There's not much capacity below this anyway.
          - 4.1 -> 100 #Set 4.05 to 100% even though it can go higher (~4.2V), for life extention.
       
      #Overide values less than 0% and more than 100%
      - lambda: |
          if (x < 0) return 0; 
          else if (x > 100) return 100;
          else return ceil(x / 5) * 5;
    on_value:
      then:
      #Publish that data is recieved
       - binary_sensor.template.publish:
          id: batt_level_recieved
          state: ON
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