Some mosquito repellents on the market use a poisonous liquid to make poisonous vapors that make mosquitoes leave the room. Due to the constant release of poisonous fumes into the room, the natural balance of the air's components for good health reaches or passes the critical level after midnight. Most of the time, these vapors get into the brain through the lungs. They also have a small or large percentage of

anesthetic effects on mosquitoes and other living things. If you are exposed to these toxic vapors for a long time, you may have problems with your brain or nerves. Here is a circuit that turns the mosquito repellent on and off after a certain amount of time. This lets you control how much toxic gas gets into the room.

The circuit periodically turns the mosquito repellent "on" and "off" for about 20 minutes each time. So, if you leave the mosquito repellent on from 10 pm to 6 am (eight hours), it will be "on" for four hours and "off" for four hours of the total time. During "off" time, the air in the room tries to get back to its natural state. Another important thing about the circuit is that when it goes from "on" to "off," it doesn't make any noise or click like a relay does, so it doesn't wake you up when you're sleeping. Circuit Operation The circuit is made up of IC 555 (IC1), which is a timer, and triac BT136, which is an automatic switch (TRIAC1). The power for the circuit comes from the AC mains. This is done by stepping it down and reversing it. By getting rid of the transformer, space and money are saved. Timer IC1 gets a steady 9V DC power supply from Zener diode ZD1 and capacitor C2. The resistors R1 and R2 and the capacitor C1 make up the timer section. Through LED1 and R4, the output of timer IC 555 is sent to the gate terminal of BT136. When the timer output goes high, it turns on TRIAC1's gate, and LED1 shows the "on" time. During "off" time, IC1's output is low, so TRIAC1 isn't turned on and LED1 doesn't light up.