Read this in other language: French
Disclaimer: This device is used to detect rainfall as early as possible in order to trigger actions. The purpose is not to measure the amount of precipitation over a given period of time (prefer to use a balancing bucket system).
Following the development of the ESPHome-based weather station, I wanted to have a system that would to have a system allowing to detect as soon as possible a rainfall in order to trigger automations in Home Assistant, especially the one used in conjunction with the roof window opening sensor.
The weather station has a rain sensor but it is a device for measuring rainfall. It works via the filling of calibrated cup mounted on a balance and the time that a first cup is filled in order to toggle the device, it has already rained the equivalent of 0.2794mm: it is already too late.
I imagined a lot of things before taking the simplest way: measuring the resistance between 2 conductors separated by a few millimeters in the hope of detecting a drop of water that would have landed between the 2.
This technique has the merit of being simple but poses some problems, the biggest of which is the corrosion of the conductors, by doing it correctly, we will be able to limit the this.
- Adjustable rain detection attempt interval (default 5 seconds)
- Temperature / relative humidity / air pressure measurement
- RGB status LED based on WS2812
- Low cost
- All functions usable with ESPHome
- MQTT
- OTA (Over The Air updates)
- The list is long
As you can see on the introduction picture, the module is installed in a waterproof box (whose screws have completely oxidized despite everything) attached to the end of a mast on top of the weather station. attached to the top of the weather station but the device is totally independent and could have been installed elsewhere.
In order to install the firmware on the ESP32, I invite you to follow the procedure described on the ESPHome website: Getting Started with ESPHome
- Reduce consumption by putting the ESP on standby between two measurements
The sensor used comes from a rain detection kit easily found on line whose photo is below.
After 6 months out, the trails are in pretty good shape.
The kit has 1 input for the sensor, 1 potentiometer to adjust the threshold, 2 LEDs and 2 outputs: one analog and one digital.
The kit is practical but is not ideal, in addition to working permanently (which will have an impact on the autonomy and oxidation of the tracks), these LEDs and its potentiometer will not serve us for anything, I preferred to use only the sensor in order to have more control over the measurements via the software.
The idea is therefore to measure at regular intervals the resistance, between each measurement, the voltage applied to the terminals of the tracks of the detection circuit is cut to limit the corrosion of the latter.
Operation:
- By default, when dry, the resistance is very high.
- When the sensor is detected as dry, every 5 seconds (variable
$measure_interval_dry), a measurement is taken and averaged, if the value + the rain detection threshold ($rain_detection_threshold) is lower than the last measurement, then it is considered as rain (or snow). - If the average sensor resistance minus the dry detection threshold
$dry_detection_thresholdbecomes greater than the last value read, then the sensor is considered to be drying.
There are a lot of configuration variables that allow you to configure everything.
Note: For the case of snow, the thresholds may not be the same and it may be possible to distinguish rain from snow
At the level of the ESPHome configuration, the whole is mainly articulated around 3 declarations:
- The declaration of the analog to digital converter
- The
resistanceplatform which usesadcto make the resistance measurement we are interested in - And finally, a GPIO switch which is the current source for the measurement
sensor:
- platform: adc
id: source_sensor
pin: GPIO33
name: ADC
attenuation: 11db
internal: true
# It is important to have a low update interval so that
# the measurement has time to be done correctly during
# the activation of the voltage AND taking into account the median filter
update_interval: 250ms
filters:
- multiply: 0.846153 # 3.9 (11db attenuation full-scale voltage) -> 3.3V
- median:
window_size: 7
send_every: 4
send_first_at: 3
- platform: resistance
sensor: source_sensor
id: real_resistance_sensor
#name: "${friendly_name} resistance"
configuration: DOWNSTREAM
resistor: $resistor_value
reference_voltage: 3.3V
internal: true
icon: "mdi:omega"
filters:
- lambda: 'return max((float)$min_resistance, x);'
- lambda: 'return min((float)$max_resistance, x);'
on_value:
then:
- if:
condition:
lambda: |-
return (
id(real_resistance_sensor).state > $min_resistance
&&
id(real_resistance_sensor).state <= $max_resistance
);
then:
- sensor.template.publish:
id: resistance_sensor
state: !lambda "return id(real_resistance_sensor).state;"
switch:
- platform: gpio
id: resistance_bias
name: "${friendly_name} resistance bias"
icon: "mdi:power"
pin:
number: GPIO19
mode: OUTPUT
I used exactly the same configuration as for the weather station.
These 3 quantities are measured by a Bosch BME280 sensor and its configuration in ESPHome is the following:
- platform: bme280
address: 0x76
update_interval: 60s
iir_filter: 16x
temperature:
name: "${friendly_name} temperature"
oversampling: 16x
humidity:
name: "${friendly_name} humidity"
oversampling: 16x
pressure:
name: "${friendly_name} pressure"
oversampling: 16xAn RGB LED type WS2812 is used to inform about the status of the assembly via a flashing script.
If you power the assembly via a solar panel or a low power source, you should disable the use of the LED.
light:
- platform: fastled_clockless
chipset: WS2812
id: status_light
name: "${friendly_name} status light"
pin: GPIO18
num_leds: 1
rgb_order: GRB
restore_mode: ALWAYS_OFF- raindetector.yaml: The ESPHome configuration file
- network.yaml: Your network information
- secrets.yaml: The secret information about your network.
