The Mosquito Repellent Project described here automatically switches on and off the mosquito repellent after a preset time interval, hence controlling the release of toxic vapors into the room. The circuit turns the mosquito repellent periodically ‘ON’ and ‘OFF’ for approximately 2 minutes 30 second each. The time period can also be increased or decreased as per our requirement.
In this mosquito repellent circuit diagram, pin 3 always oscillates back and forth from high to low during one cycle. Capacitor charges in one direction giving output and again charges in opposite direction to remain off. Consider the case when the circuit is switched ON for first time, at this time voltage at pin 3 is zero and voltage at pin 1 and 2 is high which is fed to pin 4 which is also high. Pin 5 and 6 which are connected to pin 3 through capacitor and resistor are low but after some time capacitor connected between pin 3 and 5 starts charging with the help of C1 and R1. Voltage at pin 3 also start building which is internally connected to pin 12 and 13 making voltage at output pin 11 to go low and this is supplied to pin 8 and 9. By this pin 10 becomes high and the output is produced. So, transistor starts conducting and the device connected to relay starts operating.
After preset interval of time the polarity of the charge across C1 & R1 gets reversed. Pin 4 is low and pin 3 is high. C1 again starts to charge but this time in the opposite direction. Since pin 3 is now high and pin 4 is low, the junction of C1 & R1 represents the negative side of the capacitor. As the capacitor charges the voltage at this junction falls. This means that the voltage on pins 5 & 6 will fall. When it falls to just below half the supply voltage the inputs change from high to low. And the output of gate 2 will go high. Pin 4 will take the pins 1 & 2 high so pin 3 will go low. This completes the first cycle.
If the time period has to be increased just the values of R1 and C1 has to be changed and the difference can be seen.
