Soil Moisture Sensor Circuit Help

Thread Starter


Joined Oct 29, 2016
I'm pretty new to circuitry and I was looking to make a soil moisture sensor but I need a bit of help.

I've been trying to find a soil moisture sensor diagram with a led indicator and have found two diagrams but if anyone finds any more please let me know.

My question for the first diagram is; will it work because usually there is some resistors between the LED's?

And my question for the second diagram is; do I need the zener diodes?

Thanks in advance,



Joined Sep 9, 2010
That first one will eventually destroy the first 1 or 2 (at least) LEDs from over-current. It may have meant to imply the current-limiting resistors were there. But as drawn, it's bad news.

You might prefer to use the single diode drops as in the first circuit, to get more levels. Given how crude the measurement is, I guess 4 levels is plenty.


Joined Dec 29, 2008
Use voltage output from an emitter resister into an LM3914 LED bar graph driver. ... Gives you 8 or however many you want led increments.