25-11-2017, 06:51 AM
Rain alarm project
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rain alarm ppt
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25-11-2017, 10:29 AM
The rainwater detector will detect rain and alert; Rainwater detector is used in the field of irrigation, home automation, communication, automobiles, etc.
Circuit diagram:
![[Image: Rain-Alarm-using-555-Timer-Circuit-Diagram-600x445.jpg]](https://electrosome.com/wp-content/uploads/2016/06/Rain-Alarm-using-555-Timer-Circuit-Diagram-600x445.jpg)
The heart of this circuit is a 555 Timer wired as an astable multivibrator. As you can see above, the eighth pin (VCC) of 555 is connected to the positive of the supply and the first pin (GND) is connected to the negative. A buzzer is connected to the 3edpin (output) of timer 555, so it will produce sound depending on the output of 555. Resistors R3, R4 and capacitor C1 will set the time period of oscillations produced by 555. Capacitor C2 is connected to the fifth pin to avoid high frequency noise. Transistor BC547 is connected as a switch whose collector is directly connected to the VCC. R2 is the resistance of the emitter and R1 is the base resistance of the transistor Q1.
Working
As explained above, timer 555 is connected as an astable multivibrator. Read the article Astable Multivibrator with 555 Timer for more information. The output frequency 555 is given by the following equation.
• Output frequency = 1.44 / ((R3 + 2xR4) * C1) = 1.44 / ((1K + 2x100K) x10μF) = 0.72Hz
Since the buzzer is connected to the 555 timer output, it turns on when the output of 555 is HIGH and will be OFF when the output of 555 is LOW. Therefore, when the 555 astable operates, the buzzer connected to it will produce beep sounds in a range of 0.72 Hz. The operation of 555 is controlled by the state of the RESET pin (4th pin) that is connected to the transistor BC547. 555 Timer will produce output only when the RESET pin is HIGH.
Transistor Q547 Q1 is connected as a switch. Read the article Transistor as a switch for more information about it. When the transistor is on, it will draw the current from the collector to the emitter, so the voltage at R2 will be HIGH. But when the transistor is off, it will not conduct the current from the collector to the emitter, therefore, the voltage in R2 will be LOW. When water is touched with both terminals of the rain sensor, the current will flow to the base of the transistor through the current limiting resistor R1. This turns on the transistor and drives it. This will make the RESET pin of 555 HIGH and start the oscillations.
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