The power line carrier walkie-talkie is different from the wired walkie-talkie (transmitting the audio signal directly to the other party through the wire), and is different from the wireless walkie-talkie (modulating the audio signal onto the high-frequency carrier. It is transmitted to the air in the form of radio waves). The carrier communication signal is transmitted through a low-voltage power line (a broadcast line, a closed-circuit television signal line, etc.) by using the carrier communication principle. Wired carrier communication does not require special communication lines, and does not affect the normal operation of the original line. It is easier than wired communication, simpler than wireless communication equipment, easy to install and adjust, and high in output power utilization. The carrier walkie-talkie system introduced in this paper has a total of eight walkie-talkies (can also be expanded as needed), and can call any other party without transferring. Adopting full-duplex communication mode (ie double-receiving dual-issue), it overcomes the general power carrier walkie-talkie, and most of them use half-duplex (A-B or B-A) communication, which cannot be heard and spoken at the same time. At the same time, using the music call, just plug the power plug of the walkie-talkie into the 220v mains socket. It is as convenient as the ordinary telephone. The circuit adopts the optimal design, which increases the transmission power, reduces the volume, reduces the production cost, and has a call distance of 4-5km. It is very suitable for short-distance, small-range call communication. It is suitable for business production. 1. Working principle The principle circuit of each walkie-talkie is as shown in the drawing. It consists of three parts: Power Supply, modulation transmission and reception demodulation. 220v AC power supply through the power transformer T2 step-down, VD2-VD5 bridge rectification, stabilized by the voltage regulator integrated circuit 7812 for 12v power supply. C23～C25 are power supply filtering and noise canceling capacitors, and LED8 is a power indicating LED. The modulation transmitting circuit is composed of a microphone MIC, a music calling circuit, an audio amplifier, and a filter oscillating circuit. VT1, VT2 is the modulation tube, S1 is the call button. UM66 is the music integrated circuit (commonly known as music transistor). The step-down resistor R8 can make the 2 feet get the proper working voltage of 1.5~3.5V. R7 is the bias resistor of the microphone MIC. After the language signal is converted into an electrical signal by the MIC (or the music call signal generated by S1), it is sent to the A amplifier of the TDA4920 via the coupling capacitor C12 via pin 3. R5, R6, C13 are negative. The feedback component, the amplified audio signal is output by the 1 pin, and sent to the modulation tube VT1, VT2 via C11 and R4 to amplitude modulate the high frequency carrier oscillation signal. VT3, C1~C7, T1 L1, L2, etc. constitute a carrier oscillator, the oscillation frequency range is 100-320kHz, and the modulated carrier signal is selected by the parallel resonant circuit composed of C1~C7 and L1, by L4, C20, C21 Send to 220v power line for long distance transmission. The eight intercoms that make up the communication network each have seven different transmission frequencies and one fixed reception frequency. The reception frequency is determined by the C8 and L3 parallel resonance frequencies, and the call transmission frequency is selected by S1-1 to S8-1. The synchronous linkage switches S2-2 to S8-2 illuminate the LEDs LED1 to LED7. The called telephone number is displayed. The receiving demodulation circuit is composed of a receiving detection and an audio power amplifying circuit. The other party's music call or sending signal is coupled to L3 via the power line and L1 of L1. The local receiving frequency signal is selected by C8 and L3, and the detecting circuit composed of VD1, C18, C19 and R11 demodulates the audio signal through the volume potential. The RP and C14 are sent to the B amplifier in the TDA4920 for power amplification, and the speaker BL is sounded. R9, R10, and C15 are feedback elements. C16 is the output coupling capacitor, and C17 is the power supply filter capacitor of TDA4920. 2. Component selection VT1 selects small power transistors such as 2SA1015, which requires PCM ≥ 300mw and β = 40~60. VT2 selects 2SC2228 transistor, RCM≥500mW, β=80~120. VT3 is the key to production. In order to increase the communication distance, Pcm≥750mW, β≥150, such as 2SC1941, 3DA87B, 3DG27B, etc. are required. The power amplifiers A and B select the dual audio amplifier TDA4920. The operating voltage is 3.5~13.5V. The rated output power Po=3W&TImes;2. S2 ~ S8 use double interlock switch, BL uses 16Ω or 32Ω speaker, power is greater than 4w. The MIC uses a common electret microphone, such as CRZ2-9, -15,-16, etc. In order to simplify the circuit, LED1~LED7 select domestically produced voltage-type LED BTV344052 with current limiting resistor. The working voltage is 12V. The luminous intensity is greater than 2mcd. The high frequency choke L5 can be used with a finished inductor of 10 to 22 μH. Oscillating transformer T1 needs to be self-made, choose MX-400 medium wave magnetic core, Y10mm & TImes; 50mm (circle) or B4mm & TImes; 12mm & TImes; 50mm (flat), L1 ~ L4 with ΦO.2mm high-strength enameled wire: L1 and L3 Around 20 åŒ, L2 is around 12 åŒ. L4 is around 55 åŒ. Call the music integrated circuit UM66. You can also use your own preferences to choose. Other components are labeled as shown in the drawing, and C1 to C8 are attached to the attached table. 3. Debugging method The debugging method is relatively simple, mainly to adjust the operating point of the oscillating tube VT3, that is, adjust the R1 so that the collector current is about 70 mA. If the vibration cannot be started, the two ends of the L2 can be adjusted. Then use the trimmer capacitor and repeatedly adjust at both ends of C1~C7 and C8, so that the machine receives the clearest signal, the communication distance is the farthest, and the networking calls between several machines do not interfere with each other. Due to component error and T1 winding is not standardized. As long as it does not affect the normal call, slight crosstalk is allowed. China Diy Game low price Guangzhou Ruihong Electronic Technology CO.,Ltd , https://www.callegame.com
