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I just received my first Raspberry Pi (Raspberry Pi 3 Model B+) and was thinking about starting my project journey with setting up some kind of soil moisture monitoring for the plants in my appartment (something like here). But the most of tutorials/guides for monitoring I found online detect moisture with sensors connected directly to the Raspberry Pi.

But because I would like to monitor multiple plants in different rooms of my apartment (approx. 10 m apart), I was thinking of some kind of remote/wireless connection between sensor and Raspberry Pi (eg. WLAN, Bluetooth, ...). The sensor does not necessarily need to be able to connect on its own to the Raspberry Pi (preffered, but not essential), it would also work if one or more sensors are hooked up to some kind of "port/device" to send data (but ideally the data can still be linked to the specific sensor it was taken). It is also planned that the sensors only measure and send the data once per day, in order to minimize energy consumption.

I am completetly new to the topic of Raspberry Pi, so any advices or hints no matter how trivial are welcome to help with my soil moisture monitoring project.

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MQTT is a little heavyweight for what @jonsken needs. For low power low bandwidth sensor networks where the data flows from sensor to computer the better solution would be to use a LoRaWAN, short for Long Range Wide Area Network. I won’t provide a full description here, but the Wikipedia covers it here as you might expect. In summary LoRaWAN is a low-powered, low-bandwidth, and long-range protocol. Intended to connect battery-powered remote sensors back to the internet via a gateway, on a good day, with a reasonable antenna, you might well get 15km of range from an off-the-shelf LoRa radio. The downside is that the available bandwidth will be measured in bytes, not megabytes, or even kilobytes. If you are fortunate there may be a publicly accessible LoRaWAN gateway available in your neighbourhood to connect your sensor to the Internet for free. Otherwise you’ll need to buy a LoRaWAN gateway. Your sensor will need to be attached to a lower power microcontroller such as a Pico, with a suitable LoRa hat. Complete instructions are here. Such a network should be capable of supplying data every minute for many days if not months, if you use a suitable battery for the microcontroller.

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I would recommend you to check the following:

MQTT: This is a client broker lightweight protocol and is well suited to transport messages between sensors and a central hub (MQTT Broker). And your Raspberry Pi is well suited to be a central MQTT broker.

Sensor nodes: Arduino is a MCU based hardware that has the abilities a sensor needs, ex. different inputs (analog, digital), low power consumption and easy to program. And the ESP32 or ESP8266 family of MCUs has inbuilt Wi-Fi and ESP32 has also BlueTooth.

Sensor: You referred to the resistive sensor, I would recommend that you take a look at capacitive sensors. No metallic part of the Capacitive sensor has direct contact with the soil as a resistive has.

I have done a similar system at home.

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