STC Electric Mosquito Coil Heater

Bilibili video: https://www.bilibili.com/video/BV1h14y1B7TA/
 
I. Project Description
1. An electric mosquito repellent liquid heater based on STC8G1K08 as the main controller, using a carbon film resistor as the heating element.
2. Supports Type-C 5V input and C to C cable.
3. Lower cost compared to the PTC heating element used in traditional electric mosquito repellents.
4. Can be powered by a power bank, offering portability and convenience for outdoor use.
5. Overall low hardware cost, simple circuit design, and easy to replicate.
 
II. Hardware Principle
Traditional electric mosquito repellent working principle:
Traditional electric mosquito repellents on the market operate through a self-locking switch, using a PTC heating element for constant temperature heating. Heating the wood fiber core of the mosquito repellent liquid causes the liquid in the bottle to evaporate into the air.
 
Hardware principle of this project:
1. Utilizing the Joule heating effect, when current flows through a series resistor, the current does work, consuming electrical energy and generating heat.
2. 3. A PWM-driven P-channel MOSFET AO3401 is used to control heating and stop heating.
4. A constant temperature is controlled using an NTC thermistor, reducing heating power when the preset temperature (105℃) is reached.
5. A push-button switch and an LED are used as status indicators.
 
III. Temperature Measurement Principle:
The driving and temperature measurement circuit are shown in the diagram above. The left side of the NTC resistor can be considered a push-pull output of 0V or 5V.
Because the pull-down resistor (load resistor) is sufficiently small, a RC charging/discharging delay waveform is generated on the INT1 pin at the instant of conduction or deactivation.
Combined with the trigger level of the IO pin, the resistance
principle of the NTC is somewhat similar to that of an integrating ADC. For specific implementation details, please refer to the source code. The process is as follows:
when the output is off, T1 timing and INT1 external interrupt are enabled; when the external interrupt is triggered, T1 timing is stopped. At this point, the time difference from power supply to trigger can be obtained.
This time difference can then be used to look up the current temperature in a table. Therefore, the microcontroller does not need a formula to calculate the resistance value. It's a clear trade-off between space and time.
Moreover, this microcontroller doesn't have an ADC peripheral, saving another two cents.