Cabinet lamp microwave radar module induction switch design debugging detailed description
Radar induction switch:
When it comes to the human body sensor module, many friends will first think of the "pyroelectric" sensor module, which is also our common human body sensor module based on infrared detection, widely used in the induction lamp, welcome device, intrusion alarm, including escalator entrance and exit safety tips and other products and designs. However, the application of pyroelectric module is so common, it still has disadvantages, such as: only movement, can emit infrared ray human or animal work, do not believe you try, with pyroelectric module test, you stand in front of the module do not move, see if it can "see" you. In addition, on products using pyroelectric modules, a small white hemisphere will be found on the case, which is its lens cover, meaning that it is difficult to make a hidden sensor head with traditional pyroelectric sensors.
Cabinet light microwave radar modules do not have this problem, you can hide the entire module, installed inside the sensor head, outside the see any excess components. Because it does not rely on the traditional induction probe, but use the Doppler effect to complete the detection of moving objects.
Imagine if we used the cabinet light microwave radar module to make an intrusion prevention detector, compared to the pyroelectric module, the intruder will not find any detection detector, has been detected by the radar, in addition to the advantages of the above hidden installation, other performance parameters are not inferior, its induction distance is generally 1-20 meters, can also be adjusted, as we will mention later, The induction Angle can reach about 120 °, up and down 100°.
Compared with other infrared products:
Cabinet lamp microwave radar module induction distance is far, wide Angle, no dead zone, can penetrate glass, sheet and so on. Depending on the amount of power, it can even penetrate walls of different thicknesses. At the same time, the cabinet light microwave radar module can avoid the environment in the normal working environment. The effect of temperature, dust, these advantages are not comparable to the pyroelectric module, you know, 37° ambient temperature tends to have a great impact on ordinary pyroelectric modules, which can be very embarrassing in some applications.
Circuit principle:
Sounds like such a deep detector module, in fact, the circuit principle is not very complicated. Let's talk about the working principle of its detection circuit: simply put, it is the capacitor between the collector PCB copper foil, triode internal resistance, parasitic capacitor and so on constitute RC impact circuit (high frequency triode PCB back must use copper shielding, shielding interference), impact circuit impact generated high frequency signal, through the transistor amplification, and then through the PCB three side antenna transmission.
If the microwave signal encounters a moving object, the reflected wave will change phase with respect to the transmitted wave. When the return antenna receives the reflected signal, the phase shift frequency of the reflected wave and transmitted signal will be output at low frequencies. The signal is amplified by the back operational amplifier to obtain sufficient driving voltage. We can drive the relay, which then controls the lights or other components.
In addition, we can also add a photosensitive element to the back-end drive circuit to detect the day and night light, as the premise of night control output, to achieve the drive requirements of no action in the day and night.
Key points of PCB design for microwave radar module of cabinet lamp:
I. Type return antenna:
The transmitting extreme return antenna receives the reflected signal. In order for the reflected signal to pass through the return antenna efficiently, do not cover the copper behind the return antenna. In addition, only one sinusoidal waveform is required for the return antenna. The width of the antenna can be widened appropriately. The waveform amplitude is increased, and the holes in the line are densely spaced to improve the strength and sensitivity of the induction signal (Note: The holes in the three sides of the PCB and the return wire must be filled with tinning or chemical gold to enhance the strength of the transmitted and received signal.
II. Off-base de-coupled copper foil antenna:
The rectangular antenna outside base B (between base and R rectangular copper foil antenna) serves as a capacitive de-coupling to the PCB coated copper plate on the back. If the decoupling size is too small, it is incomplete, and the induction distance is poor and unstable. If the size is too large, the induction signal will continue to be output. Generally, the size of the decoupling antenna of the 24*33mm antenna board is 3*8mm. If the antenna size is greater than or less than 24*33mm, the area of the decoupling antenna should be increased or reduced year-on-year. The shape of this decoupled antenna also depends on inductive directivity (horizontal or vertical). The shape of the long strip is perpendicular to the induction distance of the PCB board and horizontal to the induction distance in the direction of the PCB. If it's equal to the horizontal and vertical sensing distance, you can make it square, but the area doesn't change.
Transmitting frequency:
RC oscillator circuit frequency f=1/2πRC
R in the formula is the input impedance of the triode in the schematic diagram; C It is the total capacitance composed of the capacitance between the front and rear copper foil of the triode collector base lead on the PCB and the parasitic capacitance of the triode. The capacitance formula is C=εS/d, where the εmedium (here refers to the dielectric constant of the PCB board), S is the PCB plate area, d plate spacing is the PCB thickness.
Referring to the physical drawing of the cabinet lamp microwave radar module, you will find that there are four capacitors between the antennas, mainly capacitors transmitting at the same frequency, using power crosstalk for other signals and shielding filtering for WIFI signals.
There are several main factors affecting the induction distance:
A. The larger the size of the transmitting antenna board, the longer the antenna and the longer the induction distance. It should be noted here that the three sides around the antenna plate are the transmitting antennas used to transmit vibration frequency signals. The larger the antenna plate size, the longer the antenna, the stronger the transmitting signal, the longer the transmitting distance, and the longer the induction distance. However, the transmitting antenna cannot form a four-sided closed loop.
B. The higher the characteristic frequency of high frequency triode, the larger the high frequency gain and the longer the induction distance. For example, the general choice, for example, BFS520-SOT323-N2t and PRF947-SOT323-7N fT for 9GHz high frequency triodes, BFR370F.BFR360F.BFG340F fT for 12GHz high frequency triodes, in the high frequency audion the back of the copper plate, Block back in the reflected wave, improve the anti-interference ability of the audion.
C. If the magnification of the post-op amplifier increases appropriately, the magnification amplitude of the output frequency shift signal will also increase correspondingly.
D. The transmission frequency is better than the standard specification 5.8GHz. With the increase of frequency, the gain of high frequency triode will be reduced, the frequency point is too high, the transmission signal power is reduced, the receiving sensitivity is also reduced.
If properly adjusted, the ft 9GHz high frequency triode is used, the antenna plate size is 20*30mm and the induction distance is about 3-5 meters. The antenna size is 30*40mm and the induction distance is about 8-10 meters. The antenna size is 40*50mm and the induction distance will reach about 20 meters. If you want to reduce the induction distance on this basis, you can adjust and reduce the gain of the calculated amplifier on the rear amplifier plate, or change the drive level of the input to meet the requirements of different induction distances.
Fault debugging points:
1. The transmission frequency is too low (less than 5.8GHz), the anti-interference ability is poor, the reflection ability is poor, the induction distance will be long time close, resulting in false positives. The area of copper foil outside the collector and base of the transmitting signal can be adjusted, as well as the board thickness of the receiving signal circuit or PCB to improve the transmitting frequency.
2. Induction distance: the transmitting antenna is too short. The line width is too narrow, the hole is not metallized, the receiving antenna size is small, the corresponding transmitted signal strength and receiving sensitivity are low, and the induction distance is close.
3. Uniformity of the resistance container in the oscillation circuit. Consistency. Good temperature stability, should use high quality temperature drift small precision resistance, capacitance.
4. Possible causes of non-inductive failure:
A. Oscillation circuit does not vibrate: Adjust the oscillation circuit to meet the oscillation condition.
B. High-frequency triode ft too low: at least use ft greater than 9GHz high-frequency triode.
C. The antenna plate is too small, the antenna is too short, and the transmitting signal is too weak.
D. There is a problem with the triode bias circuit, which enters the cut-off or saturation region.
