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Plants wattering watcher


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Hi i've been inactive for a while but I have a question
I would like to use the plants wattering watcher (1 or 2) to monitor the moisture level in a compost pile.
but I need a little help modifying it idealy I would like to have a bar graph display (out of LEDS) Rather than a blinking led.  Battery life shoulden't be a problem I have an old solar yard light that I would like to incorperate in as the power source it has two rechargable ni-cad batterys 550mAh at 1.2 V
Also as simple as possible would be nice if there is any was to simplify it that would be nice thanks

ps. I tryed to make this post easy to read :D
I just did some tests on the solar panel and i got this

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Hi Cody,
The Plants Watering Watcher-2 project can be modified easily to produce a DC output voltage for driving an LM3915 bar-graph LED display.
Your 2.4V battery is a problem for the LM3915 since it needs a min of about 3.0V.
If many LEDs are lighted then they will quickly discharge the battery.

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ok great
my solar panel gives about 4v in bright sun could I modify the the charging circuit (witch i might have to to disable the off at day and the on at night anyway) to use 3 double a cells or if I need to I could probably use two lights so I have 2 panels and 4 batteries what would be the easyest and best?
and what about two sets of probes how easy/hard would that be?
I just got another thought what if i ran the bargraph display off the solar panel that would give it 3.5-4V and it would not be on at night which is not needed

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Hi Cody,
In the Plants Watering Watcher-2 circuit, the IC's pin 8 is oscillating at about 2 Hz, and pin 11 is Pulse-Width-Modulated at about 3kHz.
I have made pin 11 feed an inverter which is integrated with an RC pair into a DC voltage which represents the dryness between the probes.
Then I setup the reference voltage of the LM3915 as a 3.33V voltage regulator for the 74HC132. The circuit must be powered with 4 AA Ni-Cads or Ni-MH cells for about 5V.


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Ok thatks that is awsome thats the basics of what i need
now how can i use two solar panels to charge 4 ni-cads such as what the solar yard lights do
and can i have two or even three sets of probes to get a more acurate reading from the whole compost pile not just one spot?
thatks for your help so far
oh and in my schematic i left it a moving dot displayon purpose i decided that is all i need that way i save battery life and reduce power consumption

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Since your solar cells can output a max current of only 60mA and your Ni-Cads need 55mA for 14 hours, the Ni-Cads will never be fully charged and the charger is only 2 solar cells in series and in series with a diode. Any diode will be fine.

I don't know if a single circuit can have multiple probes in parallel. Maybe each pair of probes needs its own circuit. My probes for indoor plants soil are tinned thick copper wire about 55mm long and spaced about 18mm. For compost maybe they should be longer to make good contact.

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Since your solar cells can output a max current of only 60mA and your Ni-Cads need 55mA for 14 hours, the Ni-Cads will never be fully charged and the charger is only 2 solar cells in series and in series with a diode. Any diode will be fine.

that should be fine the main purpose of the solar cells is/was to extend the battery life. I can charge the ni-cads in a charger and the solar panels should keep them topped off for a while. Essentially making up for the extra draw of the bargraph/moving dot display.

I guess i can experiment with the probes i don't see what would be a problem though

For the charger just any general purpose diode right

Thanks once again for your help if i get it all worked out mabe this could be another project since this is a fairly large mod :D
EDIT: one more question the 2.5k resistor that I see in the circuit (on the LM3915) is that a POT if it is what kind linear, Logarithmic and what pot from here http://www.futurlec.com/Potentiometers.shtml would be the best to use?
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Hi Cody,
Use a 1N400x rectifier diode for the charger.

Since Futurlec doesn't stock 2.5k trimpots, use a TRIM2K in series with a 510 ohm resistor to ground.

Hi Staigen,
My plants like the very small AC current from my circuits. Maybe the current kills the bad things in the soil. Surely the current is only in a very small area between the probes and most of a compost pile won't be affected.

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Well, i dont know how i should put it, i'm not so good in the enlish language ;D
When i was young(10-15years old, about) we had an angry gardener living
here, and when we where there, trying to steal his vegetables and fruit, he
was hunting us, and to revenge we put a 1.5V battery cell with wires to his
compost. The wires was buried in the soil at each end, and the battery was
hidden behind the compost, digged down a little, and the compost did not
work. This was done in the spring, and in the spring the next year he found
the battery and reported it to the police, but they didn't cought us. This "trick"
was told to us by one of the fathers of my friends. Also, when we was going
fishing, and needed worms for the hook, we put 220V into the ground, and all
worms around immediately turned up above ground, several meters around.
As you see, i havent always been a nice guy 8) :P ;D


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I got an idea what if I took a PVC pipe and put it in the corner of the compost pile and filled it with the same material as the other compost and put the probes into that. PVC is a great insulator and that might even help if any current went out of the bottom of the pipe and into the normal soil mabe it would make the worms want to go into the compost and stay there. I don't Know but what do you think about that idea. The pipe should dry out at about the same rate as the rest of the pile woulden't you think?

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No disrespect, staigen. I am not an expert in compost, but as I understand it, the reason a flashlight type battery will ruin compost is because of the heavy metals. Not a dc charge. A nicad or flashlight type battery will have enough heavy metals to ruin a fairly good sized compost pile. This explanation makes more sense to me than the dc charge effecting worms. Otherwise, if it were due to the dc charge, the battery would soon go dead and the compost process would get on it's way again.
I certainly do agree with the mains current making the worms come out of the ground. This is how we would get the worms to go fishing when I was a kid. Got a good trickle once on wet ground, though, so I quit doing it.


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    Back when I used to go fishing, we'd got are worms by using a AC probe. What we would do is take the hot side of a power cord and tape it to a insulated screw driver, tap off the ground side, Plug it in then stick the screw driver into the ground. With in seconds the worms would pop up. The problem is that they would not live very long after that.

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Ok Hi i guess you forgot that you helped me modify this and i don't have a led i have a led bargraph display lol
my batterys are meashring a little over 5v
on pin 6 i get1.3V on pin 3 i get1.6V on pin 8 i get .64 V on pin 11 i get 2.3V
My ics are i'm guessing you want all of it so here it is
That is how my other ic looks exactly (except for a little logo i can't type
ps i don't feel any wormth on the ics if that helps

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