Cordless phone doubles as remote control circuit

When the cordless telephone base unit is combined with the control circuit introduced in this article, it has the function of a remote control receiver. Using a cordless phone's mobile phone as a remote control transmitter can control the operation of household appliances such as lights, fans, and televisions. The circuit of this controller is as shown in the figure on the right. The TP and RG terminals are connected to the telephone outside line, that is, this circuit is connected in parallel with the landline. In order to prevent malfunctions when making calls, the circuit is specially designed with the access code using the  key number as the control signal. U1 (9270) is a DTMF decoding integrated circuit. When you need to control the work of an electrical appliance, first press the call button of the mobile phone (transmitter), and then press the * key as the access code when you hear the dial tone. The signal containing the * key code information will be received by the landline, and then After being transmitted on the telephone line and transmitted to the input end of this controller, U1 decodes the signal, and its,,, and pins output the BCD code "1011" representing the * key. D2, D3, and D4 form an AND gate circuit. At this time, the base of Q1 is at high level, Q1 is turned on, the U4 (NE555) pin outputs a high level, and the four sets of electronic switches in U3 (CD4066) are opened, causing the ~ pin of U1 Connect to the A~D input terminals of U2 respectively. U2 (CD4028) is a decimal decoder. U2 cannot decode the "1011" code. At this time, its output terminals Q0~Q9 are all "0". The Q0~Q9 terminals of U2 can be connected to 10 execution circuits to control 10 electrical appliances respectively. Only two circuits are drawn in the figure, as shown in the dotted box. If you need to control the operation of the first electrical appliance, press the "1" button of the mobile phone again, then the input terminal DCBA of U2 = 0001, the Q1 terminal outputs a high level, causing U5-B to output a high level, and the relay J2 is closed. 1 electrical appliance is connected to the power supply and works. In the same way, pressing the * key and the 1 key can stop the first electrical appliance from working. As long as the * key is not pressed when making a call, the number keys pressed will not cause the control circuit to operate because there is no access code input. U1 can also choose 9170 or 8870 DTMF decoding circuit. D2~D4 can use 1N60 type diodes, or other germanium diodes with a forward voltage drop of 0.3V.  Experimental comments: The circuit introduced in this article is very novel. After assembly experiments, the original circuit can complete the functions described in the article. This circuit can only remotely control the power switch of electrical appliances, and is suitable for controlling electrical appliances with a single function, such as lights, electric water heaters, etc. However, if it is used for electrical appliances with many control functions (such as televisions), it is not so practical. If this circuit and the controlled electrical appliances are properly improved to add control functions and enhance the reliability of the controller, remote control of home appliances can also be realized, and even be sublimated into the currently popular "network home appliance" controller. Liu Huanxu, Electronic Technology Park, Sichuan University