Yesterday I tours an orchard of a friend. He consults about Moisture Meter Circuit. By this simple moisture meter circuit uses for level moistness temple of the earth. Fine the value R2 give Meter read the value has 1mA. When the moistness in the earth is in the level that wants thus Meter will read level moistness lowland value have more. For Sensor Probe use copper wire or a nail is clean all right. The transistor use 2N2222 numbers or 2N2907 or BC549 or C1815 all right. The detail is other see in the circuit.
How to build this project.
This project is not really a few components so can assemble on the small box not need to use universal PCB board. See in Figure 2 is the wiring to connects various components. The parts you needs meter I use old VU-meter it very cheap and small but can see needle meter surely. I put LED and R-39 ohms for display power on of this tool (my son like a green LED so much). The transistor can be connected with other components by not use PCB But the its Pin is not an error.
Here my son to try this tools, When the soil has enough moisture. Needle meter indicates full scale.
GET UPDATE VIA EMAIL
I always try to make Electronics Learning Easy.
Up to $20 shipping discount on first order now: https://jlcpcb.com/quote