Introduction: Moisto : Soil Moisture Sensor

About: ! Error 404 !

This instructable aims at making a very basic and simple soil moisture sensor. It could also be used as a cheap replacements to the actual soil moisture sensor modules!!!

It only uses a single transistor(NPN) which makes the project fun and simple !!!!The circuit is very simple and could also be made without using a general PCB.

Circuit schematics is attached !!


Step 1: Soldering the Components

  1. Begin by attaching the battery Holder and solder it.
  2. Solder the NPN transistor(I have used BC 547) in the right orientation.
  3. Add Led and a resistor(1K ohm) as shown in the circuit diagram.
  4. Finally make a probe like structure on the left-over PCB with the help of solder !!!


The switch in the circuit diagram indicates the probes that gets pierced into the soil !!

It could also be a piece of wire for convince and testing purposes.

Step 2: Magic of Electronics !!!

Testing :

After the circuit is complete take your PCB and pierce into a pot :

  • If pot is wet - the led indicator glows so no need to water !!!
  • If pot is dry - the led indicator doesn't glow and the pot must be watered !!!

This could be further improved by adding better battery and some more components like the power regulator , relays etc which could potentially be used to turn on or off the mini water pump so it could automate the things and make your life better (without the need of a microcontroller and it's 4x times cheaper)!!

How it works ??

If you clearly observe the circuit schematics you will notice how simple it is even if you are a rookie!!

It works in the following way !!

  • At first a small amount of voltage is passed through the LED and into the transistor !!
  • Next the threshold voltage is gained by the base of the transistor and will be further triggered by the probes to complete the circuit.
  • Whenever the probe is pierced into the soil and if the soil is moist , then the probe starts to conduct cause the water is conductive and hence the circuit is complete and the Led glows!! (vice versa)
  • In simple terms the transistor acts as a switch to trigger the LED whenever the probe gets short (here whenever the soil is wet)!!

Thank you all !!!

Happy tinkering!!