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Question on the Plants Watering Watcher circuit


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Hi Audioguru

Of course not as, any pure water getting into contact with the dirty soil will become not pure. Minerals in the soil will certainly be dissolved in water.

I wonder if there is any "soil" without minerals. If there is, then it is not suitable for plants -- plants need nutritions like N, P and K. They are normally in the form of soluable minerals in soils.

I would very much like to hear any encounter of situation that the circuit fails. ::)

Thanks.

Oli

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  • 2 weeks later...

I've just downloaded the circuits for the watering watcher..I read the text where it says A square wave is used to avoid oxidisation..my knowledge as an "improver" allows me to think that electrolysis would be the enemy of the probes..can some one explain why a sine wave is US and why oxidation not electrolysis is the nemesis of electrodes [probes]..browsing down the responses on soil conductivity...the main component of vermiculite is mica a fantastic heat and electrical insulator.. thanks guru.....dicky

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  • 1 year later...

Pure water is actually very acidic a simiconductor factory in my town uses water that has been striped of ALL minerals and the water is so thirsty for minerals that it will actually work like an acid so if someone watered a plant with "pure" water it would probably disolve the probes and the pot lol

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Hi Cody,
My tap-water has enough salts and minerals in it that it causes my Plants Watering Watcher-2  circuits to measure the same as a 47 ohm resistor between the probes. The water isn't acidic, it has dissolved conductive salts and minerals in it. "Pure" water doesn't conduct electricity and is made with distillation. Distilled water in dirt with plant fertilizer conducts fine for the circuit to indicate the amount of dryness.

My probes are just tinned copper and corrode a little. I sand and re-tin them each time (6 months to 1 year) that I replace the battery.

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  • 8 months later...

With your second circuit that has the blinking led, how would you modify it so you can have a lininer output with moisture vs voltage. would it be simmilar to the configuration of circuit one where the output does not blink. my objective is to try and connect this to the analog port on my microcontroller. Any help would be greatly appriciated

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Hi Satty,
Welcome to our forum. ;D
The circuit of the Plants Watering Watcher-2 produces a logarithmic output so it shows a very wide range of moisture levels. It would be difficult to make it linear, so use your microcontroller to convert from logarithmic to linear.

I have removed its blinking oscillator and LED driver transistors, and filtered the PWM at its output for you:

post-1706-14279143242442_thumb.png

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  • 2 weeks later...

another question the circuit seems to latch in the high state and when i abruptsl contact the probes together it goes back to the low state. My high state shorted probes is 4.65v and my low state high-z on the probes is 2.12v does this seem reasonable. I also had another question in my case i am only looking for 3 threshhold DC voltages to trigger watering, so my microcontroller will be looking for only 3 set dc voltages. Would it be easier to use the soils resistance to adjust the gain on an op amp producing a range of values based on my op amps gain. Almost like a thermister would be used for temperature. Im not doing data logging so i only need minimal accuracy say dry, medium dry, and wet. But if the output from your design is supposed to be from 2.11  - 4.65V and i van get rid of that latching effect then i can make that work.

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Hi Satty,
I have made many of these projects and they don't "latch". Did you substitute any parts?

Maybe it does something funny with a 5V supply. I can have a 100k pot beween the probes and the LED is off when the pot is zero ohms to 47 ohms then it gradually gets brighter until the pot is 100k or is not there.

Another member wanted 3 coloured LEDs to indicate the moisture level of the soil. We designed a circuit similar to yours but with opamps as comparators to drive the LEDs:

post-1706-14279143262506_thumb.gif

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