Basic knowledge of remote control circuit

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Basic knowledge of remote control circuit [Copy link]

Electric remote control toys are electric toys with remote control circuits added. Common remote control circuits generally include the following types: voice control, light control, radio remote control, etc.
Control principle of remote control circuit

　　Voice control is to use sound to control the action of the object. Generally, an electret microphone or piezoelectric ceramic piece is used as a sensor element to pick up the sound, and the circuit amplifies and drives the subsequent electronic switch to move. In order to prevent external audio interference, ultrasonic control can be used, but there are also deliberate use of audio frequency for control, such as using the sound frequency emitted by a child to control the crying and laughing actions of a voice-controlled toy doll.

　　A simple single-channel light control circuit uses the change in internal resistance of a photosensitive tube after receiving light to change the state of the electronic switch. The sensors include photodiodes, photosensitive triodes, photoresistors, photosensitive batteries, etc. (the glass-encapsulated transistor produced in the early stage, after scraping off the black shading paint on the outside, is a good photosensitive tube.). This light source can be either visible light or invisible light sources such as infrared rays. Different photosensitive elements have different spectra. More complex light control circuits can complete multi-channel switches or analog quantity change control, and are extremely widely used. It can be said that every family has one. Because the remote controls of household appliances such as TVs, power amplifiers, and VCD recorders with remote controls are typical examples of remote control using infrared light sources. In Shanghai, many corridor lights in residential buildings now use a circuit that combines light control and voice control. The footsteps, conversations, or other sounds of people passing by are used to trigger the voice-controlled electronic switches of the lights, and the light-controlled circuits are used to automatically turn off and stop responding during the day. The radio remote

　　control circuit is much more complicated than the voice-controlled or light-controlled circuit, but its main feature is that the control distance is also farther. The light-controlled and voice-controlled circuits generally have an operating distance of only a few meters to more than ten meters, while the radio remote control can be as close as a few tenths of a meter depending on the application occasion, and as far as beyond the earth to reach space! It consists of two parts: the transmitting circuit and the receiving circuit. When the receiver receives the radio waves sent by the transmitter, it drives the electronic switch circuit to work. Therefore, its transmitting frequency and receiving frequency must be exactly the same. According to the high-frequency waveform it transmits, there are constant amplitude, amplitude modulation, frequency modulation, and digital pulse transmitters. According to the number of switches it controls, there are single-channel remote control and multi-channel remote control.

Principles and characteristics of radio remote control

　　Constant amplitude transmission can only be used for single-channel control. The circuit is simple and the transmission efficiency is high, but the anti-interference ability is extremely poor. Use a fixed audio frequency to modulate the amplitude of the high-frequency transmission wave (the so-called modulation is the process of making the transmitted high-frequency radio wave change accordingly with the change of the audio frequency.), so that the amplitude of the transmitted high-frequency radio wave changes accordingly with the change of the audio frequency. This is amplitude modulation transmission. It can use different audio frequencies to control different switch channels, so it can be made into a remote control multi-channel control circuit. Since the high-frequency transmission power of the amplitude modulation wave cannot be fully utilized, the high-frequency transmission efficiency is relatively low, but because it uses the audio modulation method, it greatly improves the anti-interference ability.

　　If the frequency of the high-frequency transmission wave is modulated by a fixed frequency audio, so that the high-frequency transmission frequency has a corresponding frequency offset with the audio frequency, this is FM transmission. Because FM transmission sends high-frequency constant amplitude waves (high-frequency full-power transmission), it fully utilizes the high-frequency transmission power. Therefore, when the high-frequency transmission power of the transmitter is the same, the control distance is much farther than that of the amplitude modulation wave. Since most of the interference waves in nature are AM waves, the anti-interference performance of FM waves is far better than that of AM waves. The disadvantage is that the FM receiving circuit is more complicated than the AM receiving circuit.

　　If the audio used for modulation is not a fixed frequency, but directly uses the human voice frequency to modulate the high-frequency transmission wave, it is a radio walkie-talkie, and the basic principles of sending and receiving are the same. So when I was working on the farm, I often liked to change the radio remote control circuit introduced in the relevant magazines into a simplex radio walkie-talkie (there were few introductions to the relevant circuits of radio walkie-talkies at that time.) I had a lot of fun playing with it, because sometimes I seemed to be more interested in radio communication. If digital signals are used to modulate high-frequency transmission waves, then the transmission is a high-frequency pulse wave. Although the receiving electroplating is more complicated, all technical indicators have been improved, and the reliability and stability of the work are far beyond the reach of other modulation methods.

　　Since excessive transmission power will interfere with and affect the normal operation of other electronic equipment (passengers are not allowed to use mobile phones on airplanes, because they are afraid that the high-frequency transmission waves of mobile phones will interfere with the normal operation of electronic instruments in the cockpit and cause accidents.), each country has a special radio management committee to supervise and manage, and there are strict restrictions and regulations on the transmission power and transmission frequency of radio waves used in different occasions and different work natures. For amateur radio enthusiasts, a special amateur band is opened for use. So when you are doing amateur radio transmission experiments, don't forget these basic common sense to avoid unnecessary trouble (if you are interested, you can look at the reference materials I attached to the end of the article to learn about relevant policies and regulations.).

　　The effective distance of remote control is related to the transmission power, receiving sensitivity and working frequency. However, since the above-mentioned transmission power and working frequency are subject to various restrictions, it is generally possible to improve the receiving circuit by improving the receiving sensitivity and improving the anti-interference performance of the receiving circuit.
　　
　　The most basic radio remote control circuit uses a simple super-regenerative circuit for reception, which will produce a circuit-specific noise of "rustling..." When receiving a high-frequency equal-amplitude wave with the same receiving frequency as the transmitter, the noise is immediately suppressed, causing the input state of the low-frequency amplifier circuit in the later stage to change and drive the electronic switch to operate. Since it only generates the corresponding switch signal when the transmitter is turned on or off, it can only work in single-channel remote control mode. Moreover, when the remote control distance is extended, the circuit noise will not be completely suppressed due to the weakening of the received high-frequency radio waves. At this time, the electronic switch is in an extremely unstable critical state, either on or off, which is a taboo for remote control circuits! Therefore, the application range of this remote control circuit is very small.

　　After the AM receiver receives the high-frequency AM signal modulated by audio, the audio signal is cut off through the detection stage and sent to the post-amplification circuit. If it is a multi-channel receiver, a magnetic tank is generally used to make precision inductors to form multi-stage LC audio filter circuits with different resonant frequencies. Each stage only allows the audio frequency with the same resonant frequency of the stage to pass through, and after processing, it is converted into a DC level to drive the subsequent electronic switch. The receiver can be a combination of circuits such as direct-release, high-release, and heterodyne depending on the different requirements of the remote control occasion. In important places with high anti-interference requirements, a secondary frequency conversion circuit can be added to enhance the safety factor.

　　The focus of the radio remote control circuit is the anti-interference and stability issues, so many additional circuits may be set up in the circuit for safety. After all, the safety requirements of radio remote control circuits and radio walkie-talkies are very different. If you don't hear a sentence clearly, you can ask the other party to say it again, and you can correct it if you say it wrong. If the remote control used in important occasions makes a wrong switch action, it may result in life-threatening consequences!

　　Due to limited space, I will not introduce the receiving process and principle of the digital receiving circuit in detail here (the remote control of the color TV uses the digital signal compiled inside the IC to modulate the output of the infrared transmitting tube to achieve multi-channel control.), since there are no bulky magnetic tank inductors and other components in the digital receiving circuit, it can be made smaller through integration. The receiving circuit of the current toy remote control car has adopted IC integrated components, which greatly improves the remote control performance and also reduces the cost of production, debugging and components.

lyh94229

This is a wireless remote control, is there an infrared remote control?

feifei19870724

I have been looking for this for a long time. Thank you.