Mosquito Repelling vaporizers are generally switched on throughout night to repel mosquitoes. This is not necessary because Mosquitoes become active during the evening hours for feeding. If it enters the home in the evening, it will bite in the night also if gets a chance. So the best method is to use the vaporizer in the evening hours. This circuit automatically turns on the vaporizer around 6 pm and keeps it on till 9 pm and after that, it switches of the vaporizer. This reduces the quantity of inhaling fumes and also increases the usage days of vaporizer. The circuit can be enclosed in the switch box itself.
Transformerless power supply is used to power the circuit which gives around 15 volt DC. Capacitor C1 drops 230 volt AC to low volt AC which is rectified by the Full wave bridge rectifier module and made ripple free by the smoothing capacitor C2. Resistor R1 bleeds the stored current from C1 at power off and the resistor R2 protects the circuit from inrush current at power on. Green LED indicates the power on status.
The circuit consists of a Timer section and a relay for connecting the vaporizer to mains. Timer is built around the popular Binary counter IC CD 4060 (IC1). It is activated in the evening by using an LDR in its reset pin 12. CD 4060 is the Binary counter IC with 10 outputs which turns high one by one in a binary fashion when it oscillates using the capacitor (C3) connected to its pin9 and the resistor (R5) in its pin 10. The internal oscillations of the IC are fed to its input pin 11, so the outputs go high one by one based on the frequency of oscillation.
During daytime, IC 1 remains standby since its reset pin is high due to the conduction of LDR. When the room light reduces in the evening, LDR reduces its current flow and the reset pin of IC1 turns low. This activates the IC and it starts oscillating. Yellow LED connected in its first output (Q4) starts blinking at the rate of one in 9 seconds. After one hour and thirty minutes, Q13 of IC (Pin 2) turns high and activates the relay driver transistor T1. Relay then turns on to connect the Vaporizer to the mains through its common and NO contacts. Red LED indicates the activation of the relay. Capacitor C4 gives a short lag for the switching of T1 which eliminates unwanted relay clicking. Diode D2 removes back e.m.f and protects T1 when the relay turns off. Pot VR1 can be used to adjust the sensitivity of LDR at the particular light level in the room around 5 p.m.
Vaporizer remains on for around three hours to repel the mosquitoes. When the Q14 output (Pin 3) of IC turns high after 3 hours, relay turns off. At the same time, diode D1 forward biases and inhibits further oscillations of IC. So IC will not advances further and the Q14 output remain high till IC resets in the morning when the LDR gets light. So no need for switching the vaporizer every day and it automatically performs its duty. If there is a need for switching the vaporizer again in the night, use the manual switch S1.
Assemble the circuit on a common PCB as compact as possible to enclose inside the switch box. Give sufficient space between the power supply section and the circuit. Power supply section should be carefully assembled to avoid shorting the components. Since 230 volt AC is present in the power supply section, shorting can cause fire. It is better to construct the power supply section on a separate PCB. Enclose it in a plastic case to prevent shock hazards. Connect the relay contacts to the three pin plug as shown in the figure. Place LDR on the Switch box to get ambient day light. Light from the fluorescent lamps should not fall on LDR.
Note – 474 – 400 V ( 0.47 uF )capacitor can deliver sufficient voltage for the circuit. In places where there is voltage drop in mains, it is better to use either 105K 400 V or 225K 400 V capacitor instead of 474.
Caution: This circuit is extremely dangerous if handled carelessly since it carries high volt AC. So do not touch or troubleshoot when connected to mains.
CD 4060 Binary counter
It has 10 outputs that delivers 4.6 V at 5
V Vcc , 8.6 at 9 V Vcc and 11.6 V at 12 V Vcc so to limit voltage and current, a resistor is needed in its output. See the basic design of CD 4060 given in the website talkingelectronics