This project provides the facility of automatic switch off after the requited time duration. This is achieved by using the AT89S52 MCU. Four push-to-on switches are connected to one port of the microcontroller. These four switches are to provide four different fixed time constants.
A 16X2 LCD is connected to the microcontroller to display the status of the pump. Contrast of the LCD can adjusted by using a preset which is connected to it.
A transistor is used to drive the relay during the active time period. 5V double pole – double through relay is used to control the AC liquid pump. LED indication is provided for visual identification of the relay / load status. A switching diode is connected across the relay to neutralize the reverse EMF.
This project uses regulated 5V, 750mA power supply. Power on LED is connected for visual identification of power status. 7805 three terminal voltage regulator is used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac out put of secondary of 230/18V step down transformer.