A wireless remote control circuit

Here we introduce the circuit that uses radio frequency signals to control various electrical appliances. The number of remote control channels is 4, which can be expanded to 12 if necessary. It uses the DTMF (dual tone multi-frequency) signal in the telephone as a control code to modulate the carrier frequency of about 100MHz, and then sends it out through the antenna. The receiving circuit uses an FM receiver to demodulate the signal into a DTMF signal. This signal is then connected to a DTMF/BCD converter and converted into a BCD output, which is used to control the on and off of 4 electrical appliances. The remote control transmitter (see Figure 1) consists of a DTMF generator and FM transmitter circuit. Here, a UM91214B telephone dedicated IC is used to generate the DTMF signal, and its 3V power supply voltage is supplied by a 9V battery through the 3V zener tube D1. The circuit uses a 3.58MHz crystal as the time base circuit. The pins of IC1 are the first column pin and the first row pin respectively. They are connected through a short circuit through the switch S1 (b). At this time, the DTMF signal (tone) output by the pin is equivalent to a telephone. Dual tone multi-frequency signal sent by key 1. In the same way, , and are the second column pins and the second and third row pins respectively. When , and are short-circuited with S2 (b), S3 (b) and S4 (b) respectively, the signal output by the pins is equivalent to the telephone 2 Dual tone multi-frequency signals sent by keys No. 4 and No. 8. The remaining pins of IC1 can be used as they are. The transmitter circuit consists of transistor T1 and its peripheral circuits. The tuning circuits L1 and VC1 are tuned near the 100MHz carrier frequency. The antenna is a whip antenna, 10cm to 15cm long, and the control range is quite good. The DTMF signal is sent from the pin of IC1 to the base of T1, and then emitted outward by the antenna ANT. The receiving part (see Figure 2) consists of the FM receiver's DTMF/BCD conversion chip IC2 and a set of four trigger latch circuits IC3 and IC4. The FM DTMF signal is first demodulated by the FM receiver and then converted into a BCD signal using IC2. At this time, the digital "1" is 0001, the digital "4" is 0100... etc. IC2 also uses a 3.58MHz crystal to work. The BCD signal is sent from ~ pin to 4 D trigger latches respectively. These 4 D flip-flops are provided by two double D flip-flop chips (CD4013B), "1", "2", "4", "8" When any switch in the number key is pressed, a signal is sent to the clock input end of the D flip-flop corresponding to the number key, causing the output state of the D flip-flop to flip, thereby driving the related transistors and corresponding relays. The pull-in and release actions turn on or off the electrical appliance controlled by the relay. Since UM91214B can generate a total of 12 kinds of DTMF signals, we only need to simply increase the number of control buttons in the transmitter circuit and add a 4/16 line converter between the IC2 and D flip-flop in the receiving part, and at the same time change the D flip-flop accordingly. By increasing the number to 12, 12 types of electrical appliances can be controlled on and off.