The smoke alarm is a smoke sensing device that can indicate a fire. It is very common in homes, offices, schools and industries. In this article, the single-chip solution network will analyze its working principle and smoke alarm development program. Today, with the maturity of domestic microcontroller chip technology, smoke alarms and smoke alarms are already very cheap, their usage is increasing, and manufacturing costs are also falling. In this project, we are using simple and convenient hardware to implement the function of a smoke alarm.
1. Types of smoke alarms
1. Ion smoke alarm: there is an ionization chamber, the radioactive element used in the ion chamber-americium 241 (Am241), the intensity is about 0.8 microcuries, and it is in the equilibrium state of the electric field under normal conditions. When smoke enters the ionization chamber, it will be destroyed With this balanced relationship, the alarm circuit will issue an alarm when it detects that the concentration exceeds the set threshold.
2. Photoelectric smoke alarm: there is an optical labyrinth with an infrared pair tube installed. When there is no smoke, the infrared receiving tube cannot receive the infrared light emitted by the infrared emitting tube. When the smoke enters the optical labyrinth, it will receive the tube through refraction and reflection. After receiving the infrared light, the intelligent alarm circuit judges whether the threshold is exceeded, and if it exceeds the threshold, an alarm is issued.
Second, the working principle of the smoke alarm development program
The smoke alarm development program is a small, cheap but very practical fire alarm. In this project, a simple smoke alarm circuit with adjustable sensitivity was designed.
1. EN8F684 is the main control chip of the circuit, which can adjust the sensitivity of the circuit.
2. The output of the IO port is provided to the LED, although it can be used as an alarm. The non-inverting terminal of EN8F684 is connected to the output of the smoke sensor.
3. When the air is clean, the conductivity between the electrodes is very small, about 50KΩ. The inverting terminal input of the comparator is higher than the non-inverting terminal input, and the indicator light is off.
4. In a fire, when the sensor is full of smoke, the resistance of the sensor drops to 5KΩ, and the conductivity between the electrodes increases.
5. When the input of the non-inverting terminal of the comparator is higher than the input of the inverting terminal, and the output of the comparator is high, the alarm LED will light up and alarm.