Circuit working principle:The purpose of the system is to control the power on and off of different electrical appliances through telephone remote control. A total of 5 electrical appliances can be controlled. The signal controlling the action of the controlled object is output from p1.3 ~ P1.7. For example, if p1.3 = 1 can turn on T1, relay J1 is pulled in; If p1.3 = 0, J1 is released. If P1.7 = 1, T5 can be turned on and relay J5 can be pulled in; If P1.7 = 0, J5 is released. However, it can be seen from the figure that p1.3 is not directly connected to T1. P1.7 is not directly connected to T5, but separated by an integrated block 74LS273. 74LS273 is an 8D latch, that is, the chip contains 8 d flip flops, with d0 ~ D7 inputs and Q0 ~ Q7 outputs. If the CLR at the reset end is added with low level, the device will be reset to zero, and the outputs of Q0 ~ Q7 will be all zero. If the reset end is high level, whenever there is a level up jump at the trigger end CLK, the state of input terminals d0 ~ D7 will be locked into the device and output from Q0 ~ Q7. As long as the CLK end is no longer triggered, this state will be remembered forever. It can be seen that the signal output by AT89C2051 from p1.3-p1.7 is only memorized and then sent out, and its control logic is the same as that directly received. The necessary condition for the input end to accept the input signal is that there is a positive jump at the input end, which must meet two conditions at the same time: one is that the end of the decoder must be high level, that is, there is signaling at the remote control transmitting end; The second is to send a jump signal from ‚ 0 to 1. Only when these two conditions are met at the same time can the and gate output the positive jump signal and receive external information, which greatly improves the anti-interference ability of the circuit and prevents the misoperation of the controlled object caused by accidental interference.