Value sent from esp8266 code not the same as recieved(solved)

ESPHome
1

Hello i have a strange problem, i use custom sensor component and i send 39768182 but i receive 39768184 in HA and i just cant figure out why this is a simplified code that shows the problem
.yaml

esphome:
  name: livingroom
  platform: ESP8266
  board: esp01_1m
  includes:
    - my_custom_sensor.h

wifi:
  ssid: ""
  password: ""

  # Enable fallback hotspot (captive portal) in case wifi connection fails
  ap:
    ssid: "Livingroom Fallback Hotspot"
    password: "tAksgOaENwUm"

  
captive_portal:

# Enable logging
logger:

# Enable Home Assistant API
api:

ota:
    safe_mode: True


sensor:
- platform: custom

  lambda: |-
    auto my_sensor = new MyCustomSensor();
    App.register_component(my_sensor);
    return {my_sensor->temperature_sensor, my_sensor->pressure_sensor};

  sensors:
  - name: "My Custom Temperature Sensor"
    unit_of_measurement: °C
    accuracy_decimals: 0
  - name: "My Custom Pressure Sensor"
    unit_of_measurement: hPa
    accuracy_decimals: 0

my_custom_sensor.h

class MyCustomSensor : public PollingComponent {
 public:

  Sensor *temperature_sensor = new Sensor();
  Sensor *pressure_sensor = new Sensor();

  MyCustomSensor() : PollingComponent(15000) { }

  void setup() override {

  }

  void update() override {
	  unsigned long test_data=39768182;
  

    temperature_sensor->publish_state(test_data);

    pressure_sensor->publish_state(test_data);
  }
};

and this is what i get when i run it (same that shows up in ha)

0000 hPa with 0 decimals of accuracy
[19:52:57][D][sensor:092]: 'My Custom Temperature Sensor': Sending state 3976818
4.00000 °C with 0 decimals of accuracy
[19:52:57][D][sensor:092]: 'My Custom Pressure Sensor': Sending state 39768184.0
0000 hPa with 0 decimals of accuracy
[19:53:12][D][sensor:092]: 'My Custom Temperature Sensor': Sending state 3976818
4.00000 °C with 0 decimals of accuracy
[19:53:12][D][sensor:092]: 'My Custom Pressure Sensor': Sending state 39768184.0
0000 hPa with 0 decimals of accuracy

I just cant figure out why and its messing with the custom sensor I’m trying to write
I’m using the latest version of esphome downloaded just a few days ago
any and all tips big and small are welcome thank you!

2

Not sure if this is fixing it all, but Sensor#publish_state expects a float, not a long: https://esphome.io/api/classesphome_1_1sensor_1_1_sensor.html#a0df7b004586f6ab9eecfbabb25fcdf6c

Although, I just compared this with a custom sensor I just built, and I am sending a uint8_t value successfully through that API call.

3

Your problem is that an IEEE-754 float has an effective 24 bit mantissa (23 bits + 1 bit assuming its normalized). You can’t exactly represent that value in 24 bits, so its stored with the exponent 1 and you lose a bit of precision off the bottom.

See IEEE 754 - Wikipedia for the details.

4

What is more, that value is not in the realistic range for hPa (in the context of measuring air pressure). One atmosphere is about 1013 hPa. 39768182 is not a realistic value to test with :slight_smile:

5

Ah OK so it was that simple hmm i guess i will have to send it as text instead then, i was hoping to avoid that But thank you all very much now i know how to proceed.