[Hardware project] 2, car reversing radar design--based on special reversing radar chip GM3101 design scheme and the use of cx20106a infrared detection chip scheme comparison

Objective

Although each car has a rearview mirror, but inevitably there is a blind area of the rearview mirror, reversing radar can help the driver to remove the visual angle and blurred vision defects, improve driving safety. The previous section has analyzed the Voice module of the reversing radar (the previous section), and this section will delve into the design of the ranging module.

First, the development of reversing radar

The No. 0 generation of reversing radar: "Reversing PLEASE note"! As long as the driver hangs on the reverse gear, it will ring. (and then the egg)
The 1th generation of reversing radar: In the 1.5~1.8m from the car there are obstacles, the buzzer will work, the closer the buzzer the more rapid. (No show, test driver Ear Force)
The 2nd generation of reversing radar: Digital tube display distance digital, 3-color band green, yellow, red respectively indicate safety, warning, danger. (visual, but not beautiful)
The 3rd generation of reversing radar: The use of LCD screen to draw a car, real-time dynamic display of surrounding obstacles, anti-interference is not strong. (Beautiful, degraded performance)
The 4th generation of reversing radar: combined with the previous generations of hybrid, performance and aesthetics have improved, the price is slightly higher. (complex)
5th generation reversing radar: Integrated AV system, local tyrants dedicated, rear camera. (High-end models)

PS: Left for 2nd generation products, right for 5th generation products

Second, the principle of radar ranging

Even the 5th generation local tyrants package above is based on ultrasonic ranging, and some of the three-dimensional reconstruction using multi-probe or camera to carry out the brake safety brake scheme, just dwarfed. Only the 40kHz-based ultrasonic distance measurement scheme is presented here.

>_<: (why is 40kHz generally selected?) don't use bats to navigate me (I knew it when I was a child)! At that time we knew that bats use ultrasound to fly freely in dark caves, where ultrasound waves are more than 20kHz in frequency. The wavelength of the ultrasound is so short that it has some physical properties similar to light: ① ultrasonic similar to light, follow the law of geometrical optics, with reflection, refraction phenomenon, can also focus, so can use these properties for measurement, positioning, testing and other processing, in the transmission and the same speed of sound; ② ultrasonic wavelength is very short, with the transmitter, The size of the receiver is quite, the ultrasonic emitted by the transmitter does not spread to all directions, and become a very strong beam, the wavelength of the more powerful short direction, so ultrasonic testing, underwater detection, there is a high resolution, can distinguish very small defects or objects; ③ can produce narrow pulses, In order to improve the detection accuracy and resolution. The Pulse detection signal is very narrow, but the general pulse width of the wavelength of several times, the ultrasonic wavelength is short, so it can be used as a narrow pulse signal generator; ④ power, ultrasound can produce and transfer powerful energy. When sound waves act on an object, the molecules of the object also move with the same frequency of vibration as the frequency of the action, the higher the frequencies, the faster the movement of the molecules, and the greater the amount of energy that the object obtains is proportional to the square of the molecular motion velocity. High ultrasonic frequency, solid can give a large frequency. It is because of the sound waves in the air, with increasing attenuation of the frequency increase &&20k below the ultrasonic && frequency higher directivity, so take a compromise 40kHz.

>_<: (ultrasonic ranging principle) sound waves are defined as longitudinal waves in their media. When a sound wave receives a target object whose size is larger than its wavelength, the reflection is reflected and the reflected wave becomes an echo. It is assumed that the velocity of sound waves propagating in the medium is known, and that the time at which the sound wave travels from the source to the target and back to the sound source can be measured, and the distance from the sound wave to the target can be calculated, which is the principle of ultrasonic ranging.

PS: Remember the problem of the fool level that Junior high school did?

PS: And now the things on the tall are still so

>_<: (integrated probe and non-integrated probe) The advantages are: Single probe calculation distance formula is relatively simple, while the dual probe to some correction, more probes, economic costs and failure probability is larger, single probe is generally waterproof. The disadvantage is: the sensitivity is very poor, when the measurement distance is very far, in order to increase the transmission power, the need to use a special form of high-power transmitter transducer, but such a transducer receiver sensitivity is generally very low, need to send and receive isolation control, otherwise it will burn the circuit;

Three, distance measurement circuit scheme comparison

Using the principle of the echo distance measurement of the circuit scheme is not small, the essence of the 40kHz square wave generation circuit, rectangular amplifier circuit, echo detection circuit, the main difference is the various manufacturers adopt different methods to achieve (of course, as mentioned in the previous article also has a temperature detection module).

>_<: (Plan One: Experts say this is a fine line, but the pro-test effect is good) The program generally uses ordinary monolithic microcomputer such as 51 series to produce 40kHz square wave, the inverter is used to enlarge the rectangular waves, echo detection using CX20106A chip. The reason is that the edge is because: Ultrasonic receiver circuit is mainly composed of cx20106a and ultrasonic transducer, cx20106a is a special infrared chip, taking into account the commonly used infrared remote control carrier frequency 38KHz and the range of the ultrasonic frequency of 40KHz closer, Therefore, it is used to make ultrasonic detection receiving circuit. And the experts generally design their own standard 40kHz detection circuit (like this edge, their own design is a lot of trouble)!
In my self-made ultrasonic plane locator section (first, second, third, fourth) has been described in detail:

(send part) here uses 51 single-chip computer to produce 40kHz square wave, through the cd4011be to reverse, if only so we will find the range is very short, so the use of MAX232 signal amplification (so the effect is very good!!!) ）

(Receive part) here uses cx20106a chip, that is the irregular plan, but the effect is good ~

>_<: (Scenario II: Use of dedicated chip GM3101)

(Overview) GM3101 is dedicated to the reversing radar ultrasonic distance measurement chip, the chip provides 4-way ultrasonic probe drive, and according to the ultrasonic characteristics and the use of reversing radar environment for a series of intelligent processing, in ensuring the accuracy of ultrasonic distance measurement based on, more enhanced alarm function accuracy and practicality. The test results are encoded by two-line differential output, which improves the anti-jamming of the signal transmission. GM3101 can provide the simplest single-chip control scheme for reversing radar system, and replace the existing single-chip microcomputer control scheme. The advantage of this chip is to improve the integration of the reversing radar system as much as possible, and reduce peripheral components. At the same time the function of the chip to meet the requirements of high-end and universal, users use the group can not only produce high-performance machine products, but also the flexibility to set their products alarm mode. The whole hardware method realizes the system function, which not only reduces the user's development difficulty, but also improves the systematic performance significantly. [QFP44 Package]

(Chip characteristics)① supply voltage: 5V, operating temperature: -40℃~+85℃;② Four-way ultrasonic probe interface, probe sending drive signal [email protected];③ alarm signal encoded output, The alarm signal includes: the obstacle distance detected by each probe is dangerous level signal, the nearest obstacle azimuth signal, the nearest obstacle distance signal and the additional message, the signal level 5v;④ detection result output period 80ms;⑤ has the anti-sonic diffraction false alarm processing, enhances the alarming signal accuracy; ⑥ has the environment adaptation function, To improve the practicability of alarm function; ⑦ has intelligent recognition function, can ignore small objects, prevent false alarm; ⑧ Alarm signal output adopts two-line difference method to improve anti-jamming performance. ⑨ with anti-taking off alarm function

(structural energy) GM3101 provides 4-way ultrasonic probe interface, the chip sends and receives the super-sonic signal through the probe, calculates the distance of the obstacle according to the time difference between sending and receiving, and outputs the corresponding alarm signal. The alarm signal is encoded with two-wire differential output, the contents of the output signal include: The hazard level of the obstacle distance detected by each probe, the position of the nearest obstacle, the distance value of the nearest obstacle and the additional message. The maximum output distance is 3.15 meters and the output accuracy is 0.05 meters.

(working cycle) when the chip is plugged in, the probe drive PIN sends a driving signal to the ultrasonic probe, which drives the ultrasonic probe to send the super-sonic signal, the chip waits for the signal to return after the drive signal is sent, and the transducer receives the ultrasonic signal and sends the signal to the chip for signal amplification. The time difference between signal sending and receiving is recorded, and the distance of obstacle is calculated according to this time difference, and the alarm signal output is controlled. Ultrasonic probe Drive using the time-sharing sequence of the drive, that is, 4 probes in turn to drive, a probe in the work cycle to include the transmission and reception of two operations. 4 Probe detection complete constitutes a detection cycle. If the previous probe does not receive the returned ultrasonic signal during this work cycle, the chip is also transferred to the control of the next probe.

(operating mode selection) The chip has reversing mode and taking off mode, which can be set by the mode pin: low level or floating in reverse mode; High level is taking off mode

(reverse mode data format) alarm signal output in packet form, 3 bytes per packet:

• The first byte high four bits is the start flag, which is used to indicate whether this alarm data is in reverse mode or in taking off mode, the reversing mode is "0101" and the Taking off mode is "1010". The low two bits of the first byte are used to output additional messages, the output data indicates whether the 1 or 4 probe enters the environment adaptation mode, the S1 indicates whether the probe 1 is in the environment adaptation mode, "1" indicates the normal reversing mode, "0" indicates that the S4 indicates whether the probe 4 has entered the environment adaptation mode, "1" Indicates to enter the environment adaptation mode, "0" indicates normal reversing mode. The fourth SX1 and the third SX0 indicate the position of the nearest obstacle, 00 is the probe 1 direction, 01 means the probe 2 direction, 10 is the probe 3 direction, 11 is the probe 4 direction.

• Second byte: Sxa and SXB indicate the hazard level of the obstacle detected by the X probe, which is classified as safety, warning, danger, parking Level 4, respectively, 00, 01, 10, 11. For example, the second byte data is "10010000", indicating that the first probe detects a dangerous state, the second probe detects a warning state, and the third and fourth probes are in a safe state.

• Third byte: Outputs the distance value of the nearest obstacle, the data format, DA1 and DA0 represent the first bit of data for the nearest obstacle distance, by BCD, the maximum value is 3;DB0~DB3 represents the second bit of the nearest obstacle distance, the BCD code, the maximum value is 9;dc0 represents the third digit, 0 is 0, 1 means 5. The highest of these defaults to 1.

(taking off mode data format) in the anti-taking off function state, the chip only detects within 0.6 meters of the distance there is no object. The data output period in the anti-taking off mode is also 80ms.

• The alarm signal output is consistent with the output of the reversing mode, and it is transmitted in a standard asynchronous format and a baud rate of 4800bps, using a two-wire differential method. Anti-taking off mode, the output of the packet includes 1 bytes, the data format, the high four is the start flag, used to indicate whether this alarm data is in reverse mode data or anti-taking off mode of data, reversing mode is "0101", taking off mode is "1010". The low four-bit indication azimuth, the SX bit 1 indicates that the X probe detects a close obstacle, and SX 0 indicates that no near-distance obstructions are detected.

(typical applications) the following is a complete scenario, including a circuit that converts the in-vehicle 12V voltage into a radar operating voltage [upper left], four ultrasonic probe circuits [left middle],gm3101 and its accessory circuit [middle]

Iv. Summary

Voluminous, it's midnight! This afternoon just finished the modern control project (so busy the end of the day even if it is done), to a bedroom to clean the door and small partners talk about the selection of Office house, and quite like the sister talk about life--

She: "How long do you think it will take me to reach the annual salary of 100W?"
Me: "Grey often tired, at least 6-10 years"
She: "It feels like a long time Oh!" ”
Me: "That's the way ~"
She: "Although the light is actually good time to see"
She: "But I feel like I can't afford to wait."
She: "I'm old, I'm sure my family wants me to get married and have a baby ..."
Me: "No one can afford to wait, but one step at a pace."
She: "Then everything is in vain ..."

Even yy will chat and touch our hearts secretly hide the worry, sometimes hinder us is actually a lot of non-resistance factors brought about the helpless. Young people to be subject to a variety of intangible economic pressure and can not be free and happy life, not to wait for more than 10 years, but a lost youth. My whole body, even the most promising youth! This article was originally about the technology, but suddenly sad feeling just a bit!

Haha, the landlord is actually super see Open! I write things can give people help I am very happy, I design products so that users praise I am satisfied, I can unite a group of excellent people to do a little blood boiling things will not be wasted youth ~ (finally say OH: do not too much on the above YY dialogue, the dream is to have, in case of the reverse attack it?) Haha ! )

links

[1] at89s51 single-chip microcomputer in the design of car reversing Radar (Zhang Hanlu) (Zhang Tao) cx20106a type: Http://pan.baidu.com/s/1mgy28BY

[2] Car reversing radar system design (Wang Xiaohong) GM3101 type: Http://pan.baidu.com/s/1c0EXXRE

[3] Car reversing radar system full contact (Liu Haifeng) model description: Http://pan.baidu.com/s/1jGAHXsi

[4] GM3101 datasheet: Http://pan.baidu.com/s/1jG9wcYE

Other information (private): Http://pan.baidu.com/s/1nt9pReT

[Hardware project] 2, car reversing radar design--based on special reversing radar chip GM3101 design scheme and the use of cx20106a infrared detection chip scheme comparison