Anti-interference circuit

Anti-interference circuit (watchdog circuit): The principle of the KA555 anti-interference analog time base circuit
is shown in Figure 18-14. D4 in the figure is the KA555 analog/digital hybrid integrated circuit. Pins ② and ⑥ are input signals
, and pin ③ is the output signal. The ④ and ⑧ pins are connected to the 5v power supply, the ① pin is connected to the ground, and the ⑦ pin is
the discharge end of the transistor in the integrated circuit. Since there is a capacitor Cl: connected between the ⑦ and @ pin input terminals of KA555 and the ground, and
clz is charged and discharged through ⑦ pin, its voltage level changes continuously, the output terminal (③ pin) and the input terminal constitute
a multivibrator circuit , Rza is the feedback resistor.
    During normal operation, the microcontroller 's @PI sends out pulse signals regularly, which plays a clamping role through the diode VD3, and the oscillation circuit cannot oscillate
. Once a strong interference pulse signal is encountered and the microcontroller crashes, the oscillation circuit will immediately start oscillating and output a reset signal to
the @ pin reset terminal of the microcontroller to force the microcontroller to work again.
    After analyzing the data, the microcontroller can output instructions so that the air conditioner can continue to operate in the state before the failure, which greatly improves the anti-interference
performance of the air conditioner . This troubleshooting process takes very little time and the user cannot feel it at all when using the air conditioner.     6) Other circuits: In addition to the above circuits, there are also crystal oscillator circuits, over- and under-voltage protection circuits, buzzer circuits, power circuits , defrost circuits, etc. Readers can refer to the original circuits and analyze by themselves.