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automatic plant watering system

I have been working on this project but couldn't figure out why two 555 ICs are used and how they contributed to the operation.

JRE
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Shoeb Akter
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    The first is the off time the second is the on time. They are the timers. There is a lot of information on the web regarding the NE555 or 555 IC and how to use them. – Gil Oct 07 '22 at 15:24

2 Answers2

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The schematic has several serious flaws, such as three unterminated logic inputs, no hysteresis at the moisture sensor input and no fixed resistor in series with POT.

But the big problem is the direct connection between the U1 output and pins 2 and 6 of U2. This prevents U2 from either oscillating or acting as a monostable, because the U1 output current charges and discharges C2 much more rapidly than R3 and R4. This probably is a drafting error, but whether the relay drive is supposed to be a pulse or a square wave is not known from this schematic.

AnalogKid
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  • U2 is a monostable. It changes output when triggered, then reverts to its original state after a short pause. – JRE Oct 07 '22 at 15:35
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  • U3 (together with the probes "netPort1" and "netPort2") seems to be used in a crude moisture sensor of some kind. When the soil is dry, it triggers U1
  • U1 provides the time interval between waterings. It triggers U2 at the end of the interval.
  • U2 turns on the relay (and through to watering pump) for a short period each time the output from U1 triggers it.

The idea seems to be to provide short bursts of water while the soil is dry. When the soil has enough water, U3 shuts off U1. U2 then shuts off, and the watering cycle is done.

JRE
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