how to amplify the out put of resistance based moisture sensor

Namasthe
i am very new to the field of arduino and electronics aswell
As part of my project i came across the idea to make a soil moisture sensor with the help of just two electrodes 1 inch apart(permanent fixation with the help of epoxy) each on each poles of a speaker wire.
as per the tutorial they advised to fix a 10kohm resistor at the output end. i dipped it in water but was not getting any reading on my serial monitor unless i closed the loop with a highly conductive material between the electrodes(solder lead). then i removed the resistor and connected an LED instead of my arduino to see whether there is some light produced while i dunk it into water. A very feeble light is produced on the led while i dunk it in water. i wanted to know how i can amplify this output so that i can use it as an analog signal without destroying my arduino.
any help will be appreciated

fix a 10kohm resistor at the output end.

Not sure what that means.

A schematic of your connections and/or a clear photo of the wiring and the code that you tried would help us to help you.

The commonly advertised "moisture sensors" are generally just 24 hour "toys".

Those advertised as "capacitive" with a durable insulating coating are probably usable. :grinning:

I have a page describing that exact measurement

http://www.skillbank.co.uk/arduino/moisture.htm

I dipped it in water but was not getting any reading on my serial monitor

Probably because clean water is not very conductive. Water mixed with soil will have lots of salts dissolved in it from the soil making it more conductive.

this is the schematics

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I would expect that to give an output of 1023 from the A2D as there is nothing to form a potential divider with the sample. All you are doing is connecting 5V to the A2D input via a resistor, it is always going give its highest reading.

i have already mixed some salt in the water and the led lights up much brighter than before. ive also put a 220ohm resistor in series with the led. is there any risk in connecting the negative terminal directly to the analog pin of the uno?
thank you very much for the suggestions

this is after some modifications ive done to the circuit
now im getting 0 to 290 value on the serial monitor
any suggestions on how i can improve on this
the diode is a IN4007

I've also put a 220ohm resistor in series with the LED

LED? I don't see any LED.

I don't think you need the diode, and in any case it is the wrong way round to work.

I've never built what you are making but I suspect 220Ohms is too low. However, that you are now getting 0 to 290 is a big improvement. Experiment with higher values for the resistor, I would think anything up to maybe 10 kOhms would be appropriate, but you have to experiment to see what works best. You will get different result in soil to salt water, you will probably get different results depending on the type of soil.

Ark007 if you refer to my page I referenced above you will see you need to use a non-dc current as otherwise you will get electrolytyic action that will prejudice your results.

My circuit uses two digital outputs and two analog inputs; only 4 other components 2 diodes and two resistors.

And the sketch is there too.

http://www.skillbank.co.uk/arduino/moisture.htm

@perrybebbington you were right about the diode. i started getting a much more higher value(450) as i removed it. i changed the capacitor to a 220uf. not a significant difference in the deviation. deviation is approx 10-15 plus or minus. im gonna stick with 220ohm resistor as it hasnt caused any trouble till now.i noticed that thing about the soil type. think i have to re check and fix the value while i put it to work.
thanks for the help.

@johnerrington I looked at your link yesterday and the thing is that i dont have that particular diode so i guess i'l first see how this works and then learn from that. i am presently using a corrosion resistant electrode. i have yet to see how it is going to work. thanks for the suggestion. i will see into it

No bother Ark - its just a common small signal silicon diode. Any silicon (or germanium) diodes will do.

Even with corrosion resistant electrodes, electrolytic action will change your reading becasue of ionisation in the soild. Look at electrolysis of water - you get gas building up on the electrodes, and the current flow changes as bubbles break up.