Plant Watering Watcher Circuit problems

Discussion in 'The Projects Forum' started by Wendy, May 15, 2012.

  1. Wendy

    Thread Starter Moderator

    Mar 24, 2008
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    I am posting this for our member Hazim, as he is having some problems posting.

    I want to build and use the following "Plant Watering Watcher" circuit... The circuit s easy to understand and easy to build. In the website, they said that this is a second version (improved) for the circuit and it works well...

    [​IMG]

    I've just build it and found a problem. As I see, IC1A and R1 and C1 works as an oscillator, C2 clears the signal at specific ground humidity according to the preset R2. Now IC1B acts as a NAND gate simply, we have pin 8 high (logic) and pin 9 will be either high or low... (here is the problem). IC1C acts as a logic inverter, and IC1D along with the transistor and LED act as a flasher.

    Back to the problem. In order to have a real logic input at pin 9, this input should be either high or low, the high level here is 3V (the circuit operates on 2xAA batteries), but what I'm getting is 1.5V DC and 1.5V AC when the probes are open, when I short them I get 1.5V DC and 0V AC. So the DC value isn't changing, and so the circuit isn't functioning ok.
    The LED should either flashes (blinks) or should be off, but I see the LED always slightly lighted, there is about 0.8V~1V across it, and if I short the probes the LED turns off.

    I tried to use higher supply voltage (up to 5V) as the minimum supply voltage of the IC is 3V, but this didn't solve the problem. Please don't recommend other ICs of completely different ideas because it's hard to get IC like 74HC132 now and because I've built the circuit on a PCB (before testing [​IMG] )

    Any help is strongly appreciated.

    Regards,
    Hazim

    Website of the circuit: http://www.redcircuits.com/Page18.htm
     
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  2. hazim

    Active Member

    Jan 3, 2008
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    Thank you. I still not able to post a new thread...
     
  3. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What happens if you disconnect pin 5 if the IC from pin 3 of the IC and connect pin 5 to the + of the powersupply?
    I would expect the led to flash.

    (this to seperate the circuit parts for toubleshooting).

    Bertus
     
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  4. Audioguru

    New Member

    Dec 20, 2007
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    The original circuit used a CD4093 and also didn't work. I fixed it years ago (as a new project at www.electronics-lab.com) and used a 74HC132 IC that works fine when the battery has dropped to 1.5V or less.

    The improved RED CIRCUIT version copied parts of mine but kept the CD4093 that does not work when the 3V battery voltage drops a little.
     
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  5. #12

    Expert

    Nov 30, 2010
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    I logged in just to put a "thanks" on AG. This is the kind of problem that drives people nuts. Even people with experience fail to doubt the chip selection until all else is exhausted.
     
  6. hazim

    Active Member

    Jan 3, 2008
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    Hi.
    I found 74HC132 IC (SMD) in an old board. The IC is ok. I build the circuit of this IC but I have some problem with it. First of all, I used 3.3MΩ resistor instead of the 3.9MΩ one for R3, and I used two 100nF capacitors in parallel instead of the 220nF one for C4, and used a 2.2nF and a 2.7nF for C1 and C3. Also I used a 100k pot instead of R8 so I can adjust the sensitivity.

    I don't know whether the values are critical or not, and so if that's the cause of the problem.
    The LED flashes perfectly when the probes are open, and stop flashing when I short them. The problem is that if I put the probes in water, the LED still flashes but with dimmer light, and this depends on the pot adjustment off course. I tried to adjust the pot by decreasing the resistance, the LED stop flashing at very low resistance (5~10kΩ approx.), and if I took the probes out from water the LED will not flash again (because the pots resistance was much lower that that of water, and so water has no effect) or it may flash but dimmed.

    I had build two circuits and had "approximately" the same problem... What do you think? or recommend?

    The big picture is for the 74HC132 circuit, and the other is for the 4093 one.

    [​IMG]

    [​IMG]
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    3 circuits have been posted. We don't know which circuit you built.
    R3 was 3.9M in my circuit but it does not have an R8.
     
  8. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
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    Audioguru,

    For clarification, which circuit are you recommending? You posted three circuits and said your circuit doesn't use R8. However, you also said you fixed this circuit and posted it on electronics-lab.com. I presume you mean this one: http://www.electronics-lab.com/projects/science/002/index.html?

    This circuit uses R8 across the probes.

    The circuit here http://www.redcircuits.com/Page18.htm matches the third circuit you posted at the bottom, but you said it should use a 74HC132, not a CD4093. I then presume that the circuit and all components on redcircuits.com is the one you recommend once the IC is replaced with 74HC132?

    Great work by the way. I think I'll build several of these soon for our plants at home.
     
  9. #12

    Expert

    Nov 30, 2010
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    The problem is that you are calibrating it for water then expecting it to do something not related to just water in a cup.
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    OOps!
    Yes, my circuit has R8 and it works fine with no adjustment needed.
    Damp soil with fertilizer salts in it causes the LED not to light then the battery lasts for a long time. My tap water also causes the LED not to light.
    Dry soil or pure distilled water causes the LED to blink brightly. The duration of each blink is short so the average battery current is low.
    The LED brightness depends on how dry is the soil.

    The first circuit from RED Circuits does not work and kills the battery quickly. I didn't try the newer second circuit there so I don't know if it works.

    The minimum supply voltage for a CD4093 is 3.0V but the 3V battery will drop to 2.0V so a CD4093 should not be used.
    The minimum supply voltage for a 74HC132 is 2.0V but many still work with 1.5V.

    The pin numbers are different for a CD4093 and a 74HC132.
     
  11. hazim

    Active Member

    Jan 3, 2008
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    I said that I built the circuit of 74HC132 and it's which I have problem with for now, again this is it: http://www.electronics-lab.com/projects/science/002/index.html

    You didn't tried to help me find the problem. Is using 3.3M instead of 3.9M for R3 what caused the problem? or using different values for C1 and C3 (2.2nF and 2.7nF), or using 200nF instead of 220nF for C4? are the values critical?

    I found that even when shorting the probes, the LED blinks but very dimmed, and when their is a few kilo ohms resistance between the probes the LED blinks brighter so it blinks in wet soil.. (even if R8 is 1M Ohm). I think either there is a problem in the circuit itself, of the values are critical and so I had the problem. If you see the problem is with capacitors' values, can I use ceramic disk instead of polyester capacitors?
     
  12. Audioguru

    New Member

    Dec 20, 2007
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    My circuit uses ordinary part values that should be available anywhere.
    Since you used different values then the performance is different.

    I used polyester capacitors because they are inexpensive and have a tolerance of 5%. Ceramic capacitors might have a tolerance of +80%/-50%.

    R3 and C4 determine how often the LED blinks. Mine blinks about 2 blinks per second but yours will blink a little faster.

    C1 and R1 determine the switching frequency and AC frequency at the probes.

    C3 and R2 and R8 determine the brightness of the LED with certain resistances beween the probes.

    Mine blinks brightly when there is nothing (dry soil) between the probes. The LED blinks very dimmly when 100 ohms is between the probes. When the probes are shorted then the LED is not seen in a dark room.
     
  13. MrChips

    Moderator

    Oct 2, 2009
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  14. Audioguru

    New Member

    Dec 20, 2007
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    The previous thread simply uses DC which causes plating and unplating of the probes.
    The "Plants Watering Watcher" circuit uses a more complicated AC signal at the probes to avoid plating and unplating and a more complicated blinking and dimming LED circuit so the battery lasts a long time.
     
  15. hazim

    Active Member

    Jan 3, 2008
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    So.. I tried to solve the problem in several ways but it still exists, i.e. when the resistance between the probes is say 56 Ohm, the LED blinks dimmly about 1/2 of full brightness as when probes are open.. and I still can see the LED blinking when shorting the probes (but it's very dimmed).
    Why is that happening? What to do?
     
  16. Audioguru

    New Member

    Dec 20, 2007
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    With nothing between the probes the LED is supposed to blink brightly to warn you that the soil is dry.
    With 56 ohms or 100 ohms between the probes the LED is supposed to blink dimly because the soil is damp.
    With the probes shorted then the LED is supposed to be turned off because then the soil is wet.

    I have two circuits here that use 1nF 5% poly capacitors for C1 and C3 and both work like that.
    Maybe your water has more or less salts (conductive) than my water.
     
  17. hazim

    Active Member

    Jan 3, 2008
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    56Ω is very low resistance and is much less than the resistance of damp soil. What to change in order to increase the sensitivity for damp soil? I'll try to use 1nG for C1 and C3.
     
  18. Audioguru

    New Member

    Dec 20, 2007
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    Increase the surface area of the probes. Mine are 0.7" apart, are made of 1mm tinned copper wire and are 6cm long.
    Decrease the value of R2 and/or increase the value of R1.
    I did not try changing resistor values because my projects are glued to the battery holders.
     
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  19. hazim

    Active Member

    Jan 3, 2008
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    Actually the circuit didn't worked fine. I don't know what's the problem, I tried everything possible to solve it...
    I'm looking forward designing a new circuit. How could I use a NAND gate as a comparator?
     
  20. Audioguru

    New Member

    Dec 20, 2007
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    What do you want to compare? Dry soil or wet soil? Then the LED is simply on or off.
    My circuit uses pulse-width-modulation so that the LED has millions of levels of brightness.
     
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