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tags: IoT

A simple plant monitor for Homeassistant

ja225huTue, Jul 12, 2022 After running this for a while, the water level sensor has corroded rather rapidly, leaking copper into the soil/water, this is obviously not desirable, to prevent this a capacitive moisture sensor would be ideal, but changing the setup so that the extant sensor is powered via one of the GPIO pins, and only powered in short, infrequent bursts while measuring would limit corosion and extend the lifespan of the sensor from a few days to several weeks or months.

Hello! I am John Åkerhielm (ja225hu), this is my tutorial for a simple IoT device for monitoring a plant's environment.
Time required; 1-2 hours.

Objective

I'll be able to determine how fast my plants dry out, and automatically logging when I am watering them.

Materials

Item	Price	Link
Esp32 development board	167 sek	amazon.se
37 Sensor kit	282 sek	amazon.se

Since I knew I wanted to stay in the smarthome arena, I decided that a wifi based device makes the most sense, both from a deployment (every home has wifi already), and development perspective.
I purchased the sensor kit since it was pretty cheap and a fun bunch of things to have. For this project I used:

• DHT11 Temperature & Humidity Sensor
• Water Level Sensor

Computer setup

I use MicroPython which I downloaded from the Micropython website. My development board has an esp32-wrover-b so I used the esp32spiram release of MicroPython.
Flashing was unproblematic. I just followed the instructions and flashed the device with esptool.py:

esptool.py --chip esp32 --port /dev/ttyUSB0 erase_flash
esptool.py --chip esp32 --port /dev/ttyUSB0 --baud 460800 write_flash -z 0x1000 esp32-20190125-v1.10.bin

I prefer to use a simple text editor to write code, and manually upload to the device via terminal.
I found small script called mpfshell that very neatly sends files to the device.

git clone https://github.com/wendlers/mpfshell
python3 setup.py install --user
#dont use pip to install it, version 0.92 is broken

I made two shell aliases to makes things neater.

#uploads all files in esp32/device_root to the esp32 device.
alias mpfs_USB_SYNC='mpfshell -n ttyUSB0 -c "lcd /home/john/d/p/esp32/device_root;mput .*"'

#opens a python interactive shell (REPL)
alias mpfs_USB_REPL='mpfshell -n ttyUSB0 -c "repl"'

Putting everything together

The 'DHT11 Temperature Humidity sensor' and the 'Water Level Sensor' each use a single input pin, as well as 3.3V and GND.
I connect the DHT11 to pin 33 and the Water Level Sensor to pin 32.

Platform

I run a local homeassistant instance and a mosquitto mqtt broker, this keeps all my data in-house. Homeassistant does the logging, display and processing of data.

homeassistant and mosquitto are run as docker containers, this makes install, reinstall migration very easy. Also: all the components are free and open source.

To install homeassistant using docker-compose (get it this from your distros repository).
create a file called docker-compose.yaml:

services:
  homeassistant:
    image: homeassistant/home-assistant
    network_mode: host
    restart: always
    volumes:
      - ./homeassistant/config:/config
      - /etc/localtime:/etc/localtime:ro
  mosquitto:
    image: eclipse-mosquitto
    ports:
      - 1883:1883
      - 9001:9001
    restart: always
    volumes:
      - ./mosquitto:/mosquitto/config

and then run

docker-compose up -d

in the same folder. More info here

The code

The code is very simple

https://gist.github.com/fyra/2cfcfd639ed932714db77d038cbdfb2e

## Code for a plant-monitoring device.

#some builtin libraries, most notably; dht contains the driver for the temp-humidity sensor
import machine, time, dht, binascii, json

#using umqtt as mqttclient from https://github.com/micropython/micropython-lib/
from umqtt.robust import MQTTClient

#temphumidity sensor on pin 32
thsensor = dht.DHT11(machine.Pin(32))

#water level sensor on pin 33
water = machine.ADC(machine.Pin(33))

## ip address to  my mqtt broker
server = "192.168.4.14"

identifier = binascii.b2a_base64(machine.unique_id())[:-1].decode()

# configuration for homeassistant sensor, makes the plant show up in Homeassistant automatically.
conf_t = { [...] }
conf_h = { [...] }
conf_w = { [...] }

#connect to the mqtt broker
c = MQTTClient("umqtt_client", server, keepalive=60)
c.connect()
time.sleep(0.2)
c.publish(f"homeassistant/sensor/{identifier}_humidity/config", json.dumps(conf_h).encode(), retain=True)
c.publish(f"homeassistant/sensor/{identifier}_waterlevel/config", json.dumps(conf_w).encode(), retain=True)
c.publish(f"homeassistant/sensor/{identifier}_temperature/config", json.dumps(conf_t).encode(), retain=True)
c.disconnect()
time.sleep(0.2)

#And finally an infinite loop that updates the sensor every five minutes.
while True:
	thsensor.measure()
	status = b"{" + f'\
"Temperature":"{str(thsensor.temperature())}",\
"Humidity":"{str(thsensor.humidity())}",\
"WaterLevel":"{str(water.read())}"\
' + b"}"
	c.connect()
	c.publish(f"tele/plant_{identifier}/STATUS", status, retain=True) 
	c.disconnect()
	time.sleep(360)

Transmitting the data / connectivity

Data is published to the local MQTT broker over wifi.
Homeassistant sees the topics in homeassistant/sensor/ and automatically recognizes them as sensor entities.

Using the data

I am using Homeassistant to log and display the data.
Homeassistant is a very easy to use platform for automation, so I might add a small pump for automatic watering of some plants eventually.

In Conclusion

This project produced a passable prototype, next refining step would be evaluating the Water Level Sensor and calculating a percentage rather than the unsigned 12bit value that it currently is.

After that i'd want to physically design the device.
Those wires are not pretty.

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