Infrared emission and receiving head (infrared basic knowledge)

April 05, 2024

At present, there are two kinds of commercially available infrared integrated receiving heads: level type and pulse type, most of which are pulse type, and there are few level types.
Level type, receiving continuous 38K signal, can output continuous low level, the time can be infinitely long. Its internal amplification and pulse shaping are directly coupled, so it can receive and output continuous signals.
Pulse type, can only receive intermittent 38K signal, if receiving continuous 38K signal, it will remain high after several hundred ms, unless the distance is very close (within twenty or thirty centimeters). Its internal amplification and pulse shaping are capacitively coupled, so it cannot receive and output continuous signals. For general remote control pulse type, only special occasions, such as serial port modulation output, because the serial port may continuously output data 0, so use level type. The general remote control uses 455K to divide by 12 and output 37917HZ, referred to as 38K, 10m receiving bandwidth is 38+-2K, and 3m is 35~42K. In an open space without environmental reflection, the directivity of 10 meters or more will be stronger. Indoors, if the wall is white, there is basically no directionality in the space of 15 meters.

The receiving head should have a filter to filter out the white light. It will affect reception under the following environmental conditions, even severe:
1. The strong light directly hits the receiving head, causing the photosensitive tube to saturate. The white infrared component is also very strong.
2. There is a strong infrared heat source.
3, there are strobe light sources, such as fluorescent lamps.
4, strong electromagnetic interference, such as fluorescent lamp start, motor start and so on.

38K signal is best to use 1/3 duty cycle, this is the most commonly used, according to the test 1/10 duty cycle sensitivity is better. The actual modulation time is less than 50%. It is best to have a break.

The level-type receiver receives a 38K infrared ray and outputs a low level. It is very cool to use. Most of the old-fashioned receivers used this type, but they have a fatal weakness: poor anti-interference and short transmission distance. (less than 1m).

The pulse-type integrated infrared receiving head must receive the baseband signal of a carrier with a certain frequency of 38K for normal output, such as transmitting a 38K carrier of 500HZ, and the pulse-type integrated infrared receiving head outputs a 500HZ square wave, and if a continuous 38K carrier is transmitted, There will be a phenomenon in which there is a moment of low level and then a high level. The pulse type integrated infrared receiving head overcomes the shortcomings of the conventional level type receiving head: the transmission distance is relatively far, the stability is greatly increased, and the anti-interference is stronger. Therefore, it has completely replaced the old-fashioned level-type accepting head. In the electronic market, it is absolutely impulsive to tell the owner that it is given to you.

When the mobile phone is photographed, you can check whether the infrared transmitting tube is in the transmitting state.

Some red manufacturers have the ability to create a red-violet-free infrared light as a technical issue to promote, as if there is a red storm is low technology, no red storm is high technology. In fact, whether or not red storm is only a matter of choice, not a technical problem, the light with a wavelength of more than 700 nm is called infrared light, and the infrared light of 900 nm or more is basically no red storm. The shorter the wavelength, the stronger the red storm and the higher the infrared sensitivity. There are two mainstream infrared lamps on the market. One is slightly red, the wavelength is around 850 nm, and the other is red-free. The wavelength is around 940 nm. The same camera, the sensitivity at 850nm wavelength is 10 times better than the sensitivity at 940nm. Therefore, the 850nm infrared light with a slight red storm has higher efficiency and should be used as a preference for infrared night vision monitoring.
Does this make sense?

Red storm is a description of the working state of the infrared light. When the work light is working, if there is a red storm, a red dot will appear in the die. If there is no red storm, the work and the non-working people can't see it. No red spots

Both 850nm and 940nm have red bursts, but 940 is weaker.

Common infrared emission tubes are 940nm wavelength and 850nm wavelength. The 940nm wavelength infrared emission tube is mainly used for modulation coding and signal transmission, while the 850nm wavelength is mainly used for security and other infrared light sources, and the receiving tube is 850nm~950nm. Model . The difference between the 850 tube and the 940 tube is their power level. The 850 is a high-powered one. It is characterized by a short transmission range and high sensitivity, which is suitable for use in video surveillance. 940 is a small power, it is characterized by: long transmission distance, low sensitivity, mainly used on the remote control

850 launch tube selection

The general design of the integrated machine is relatively close. Generally, it is suitable for IR emitter tubes with larger angles. The most common 45 and 60 degree angles on the market, you can choose general wafers. It is best to choose Japan and Taiwan. The market uses 12Pcs, 14Pcs, 18Pcs, 24Pcs launch tube integrated machine, commonly used such products generally develop distance of 5-20 meters, if the development of more than 20 meters of all-in-one machine, it is recommended to use Japanese and Taiwan wafers, such as 28Pcs, 36Pcs, 48Pcs, 64Pcs and other products, At the same time, it is better to use a smaller angle.

If your modulation waveform is active high, the 38KHz receiver output is definitely low;
Almost all of the infrared receiver's output signals are inverted

There are usually a lot of receiving heads. After a long time, I can't tell how the three feet are arranged.
The method is to measure the resistance of the two feet with a mechanical meter, and find the one with the smallest resistance of the two feet. At this time, the watch stick does not move. The answer comes out: the red watch is connected to Vcc, and the watch is connected to the ground. Oh, it goes without saying that the other foot is the signal foot (IR).

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Mr. Terry

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