This is a project of an automatic plant irrigator circuit with 555 IC. The circuit is able to water your plants automatically when you are away from home. A relay switch is connected at the output of the circuit from which you can connect the water pump. The operating voltage of the circuit is 9 to 12V DC.
The circuit can be divided in to two parts fast part is a moisture sensor circuit and the other is a timer circuit build around a 555 timer IC. The two probes shown in the circuit should be inserted in the soil of your plants. These two probes detect the water contents in the plant soil. If there are enough water contents in the soil of your plants then the relay will be in off condition. But when there is not enough moisture contents in the soil or it become dry then the circuit will activate the relay switch for a preset time and therefore any pump that is connected with the relay will be switched ON.
The preset time of the activation of the relay switch can be adjusted with the 1M variable resistor. The preset time can be increase by further increasing the value of the capacitor Cx.
The sensitivity of the two probes can also be increase or decrease by adjusting the 50K variable resistor to switch on the relay on the desired dryness of the soil.