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query abt plant watering watcher I


meshal

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hello,
I 've already made it and it is working successfully.
but i have some confusion about working of the components given below. 


I need full description of this project especilly the working of
* each gate of IC
*diodes
*outputs when test it with logic tester
*probes
*variable resistor]
plz reply me soon

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Hi Meshal,
Welcome to our forum. ;D
I and others have built the 1st version of the circuit and it didn't work:
1) Many makes of its IC don't work with a new 3V battery and the Motorola IC that does work at 3V fails when the battery voltage runs down a little.
2) The circuit doesn't dim its LED. The LED simply switches on very dimmly or is off.
3) The probes corrode quickly or one is unplated due to the unsymmetrical waveform.
4) If it works then its battery doesn't last very long.

Doesn't your circuit have any of the above problems?

I recommend that you build the improved 2nd version. Its project describes the function of its parts in detail. http://www.electronics-lab.com/projects/science/018/index.html
;D

post-1706-1427914241862_thumb.png

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hi,
thanks for ur reply.
I didn't  face any such problems in my circuit. it is working successfully i only need the use of diod,capacitor(c1),r1,r2,probes(how it work with signals that is in dry &wet soil).why we use variable resister.also what should be the states on each gate(either high or low in both dry &wet cond).
waiting for reply  :)

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Hi Meshal,
In the Plants Watering Watcher I project:
1) IC1d is a Schmitt-trigger oscillator and uses D1 and R2 to quickly charge C1 which causes its duty-cycle to be so that its output is low for most of each cycle.
2) IC1a is an inverter.
3) IC1b and c are paralleled NAND gates which drive the LED.

When there is nothing between the probes then the inverter drives both inputs of the NAND gates and their output follows the oscillator's output and lights the LED for most of each cycle.

When there is a low resistance between the probes then the oscillator feeds one input of the NAND gates and the inverter feeds the other input through the pot. Therefore one input of the NAND gate is low at any time causing its output to be high and the LED is turned off.

When the resistance of the soil between the probes is at a certain value that the voltage divider action of the pot and the soil's resistance causes the voltage of the divided signal to equal the Schmitt trigger threshold voltage of the NAND gates then the LED will either turn on or turn off.
The pot is adjusted to match the resistance of the soil since salty soil conducts more.

The LED just switches on or off. Without having C3 that I added to my circuit, I don't see how it is possible for the LED to dim. The LED will be very dim anyway since a CD4093 has a very low output current with a new 3V battery and either won't work or have a much reduced output current when the battery's voltage runs down.

My improved "II" circuit dims the LED gradually from off to very bright, even when the battery voltage is only 2V. Since my circuit blinks the LED then its battery lasts a long time, and so I could use little AAA cells.
I didn't use a pot in my circuit since it indicates a very wide range or resistance. 47 ohms or less causes the LED to be off, 100k or more causes its LED to be its brightest. ;D

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Hi meshal,
Glad to hear that you have had success with this circuit. Others have also built this circuit with no problems.
I am only curious if you used the Motorola chip or another manufactirer's chip. There was some controversy about different results being dependent upon this chip.
Thanks for the feedback.

MP

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