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?

http://www.seekic.com/uploadfile/ic-circuit/20115143378538.gif

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

http://www.circuitdiagram.org/images/led-moisture-level-meter-circuit.gif

Thanks in advance,

Tyler

 

Just a suggestion ... This is a relatively simple dc circuit. You could download the free ltspice simulator :
http://ltspice.linear-tech.com/software/LTspiceXVII.exe
... and see if you could put one or two of your circuits together. Use a 2N222 type transistor, and maybe a 0.1 volt dc voltage source for the initial conductance related input of the probes.

 

Is it worth the effort?
http://www.ebay.co.uk/itm/3-in-1-Ga...426686?hash=item236ee610be:g:3wgAAOSwuWVWFMGQ

If it is then the second circuit looks OK and, no, you don't need the zeners.

Or the expensive solution:
http://www.ebay.co.uk/itm/GSK-908-S...359995?hash=item2ef38957bb:g:3T4AAOSwgZ1XwCzB

 

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.

 

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