six big skills to Chooses the PCB components

1. to consider the part package choice. 
In the entire schematic diagram plan stage, we should consider the confirmation of the part package which makes in the domain stage and welds the plate design decision.Below has given when according to the part seal choice part needs to consider some suggestions
2 use good earth method.
Guarantees that there is enough shunt capacitance and horizon.When use integrated circuit, guarantees arrives in the nearness power source end (should better be horizon) position use appropriate decoupling electric capacity.The electric capacity appropriate capacity is decided by the concrete application, the electric capacity technology and the operating frequency.When the bypass electric capacity lays aside between the power source and the earth pin, approaches the correct IC pin place, may optimize the electric circuit the electromagnetic compatibility and the susceptivity.
3. assignment hypothesized part package.
Prints bill of materials (BOM) to use in inspecting the hypothesized part.If the hypothesized part correlation package,it can not be able to transmit to the domain stage.Founds a bill of materials, then in examination design all hypothesized parts.The only clause should be the power source and the place signal, because they were considered is the hypothesized part.If only carries on special processing in the schematic diagram environment, cannot be transmitted to the domain design.Only if uses in the simulation goal, demonstrates the part in the hypothesized part all to be supposed to use to have the seal part substitution.
4. guarantees you to have the integrity bill of materials data.
whether The inspection bill of materials reported has the enough integrity data or not ?After founds the bill of materials report, must carry on the careful inspection, to all part clause in incomplete component, supplier or manufacturer information supplement integrity.
5. To sort according to the components marking .
In order to be helpful to bill of materials sorting and the examination, guarantees the part marking is the continual serial number.
6.to inspect unnecessary gates.
Generally speaking, all unnecessary gate input all should have the signal connection, avoids the input end being hanging.Guaranteed you to inspect all unnecessary or the omission gate, and all did not have the segment input end all completely to be connected including the above.In some situations, if the input end is at the suspended state, the overall system all cannot work correctly.Take the double transports puts for example,to which is used frequently in the design .If the double land transport put in the IC part only to use one to transport puts,The suggestion either transports another puts also uses, either will not use the input end earth which will transport puts.And the cloth puts an appropriate unit gain (or other gains) feeds back the network, thus guarantees the entire part to be able the normal work.

Analysis of circuit board welding defects

There are three main factors that cause welding defects:

*The weldability of the hole affects the welding quality.

It will cause weld defects if the hole welding is not good, affect the component parameters in a circuit, and lead to the instability of multilayer board components and inner conductor, and finally cause failure of the entire circuit function. The so-called weldability is that the metal surface is wetted by the molten solder, that is, the solder metal surface to form a relatively uniform and continuous smooth film.

*Weld defects due to warping

Circuit board and components in the process of welding warp, due to the stress deformation and weld defects such as short circuit. Warpage is often due to the temperature of the upper and lower parts of the circuit board caused by the imbalance of the board itself due to the weight of the warp.

*PCB design affects welding quality

In the layout, the size of the circuit board is too large, the printing line is long, the impedance increases, the anti noise ability drops, the cost increases.

How to optimize the PCB file?

1.Shorten the connection between high frequency components, reduce EMI interference.

2.A heavy weight (e.g., over 20G) element, which is supported by a bracket, and then welded

3.Heating element to consider the problem of heat dissipation, heat sensitive components away from the heat source.

4.The arrangement of the elements is as parallel as possible, so that the utility model can be beautiful and easy to weld, and is suitable for mass production.

Welding methods and skills for a new PCB board

For the new PCB board, we must look at the board first, whether there are problems, such as whether there are obvious cracks, there is no short circuit, open circuit, etc.

If necessary, check if the resistance between the power supply and the ground is large enough. Then install the component. In general, the power can be installed in the first part, and then on the power supply output voltage detection is normal. If you do not have too much confidence in the grasp, it’s a good idea for adjustable regulated power supply with current limiting function. The preset is better than the current protection, and then the voltage of the power supply is slowly increased, and the input current, input voltage and output voltage are monitored. If there is no over-current protection and other issues during process, and the output voltage is also normal, then the power part OK. 

There are several ways to find fault.

Measuring voltage method

First of all, we must confirm that the power supply voltage of each chip is normal, and then check the reference voltage is normal, there are other points of the operating voltage is normal, etc.

Signal injection method

The signal source is added to the input end, and then the waveform of each point is measured in turn to see if the fault is normal to find the fault point. Sometimes we use a simpler approach, for example, with a hand holding tweezers to touch the input at all levels to see whether the output response, if you do not respond to the first level, and after the first reaction, then the problem at the previous level, should focus on inspection.

Of course, there are many other ways to find fault points, such as seeing, hearing, smelling, touching, etc.

"Look" is to see whether there are obvious mechanical damage components, such as rupture, burning black, deformation, etc.

"Listen" is to listen to the sound of the work is normal, such as something that should not ring in the ring, the sound of the place does not ring or abnormal sound, etc.

"Smell" is to check whether there is a smell, such as the smell of burning, the taste of electrolytic capacitors, etc., for an experienced electronic maintenance personnel, the smell is very sensitive.

"Touch" is to use the hand to test whether the device temperature is normal, such as too hot, or too cold. Some power devices, should fever when work, but if it is cold, it can be judged that it does not work. General power transistor, voltage regulator chip, working at 70 degrees below is completely no problem. 

flight controller hardware structure and circuit2

Comparing uav remote sensing satellites and manned aircraft platform, has the characteristics of low cost, high flexibility.In order to satisfy the science remote sensing experiment, remote sensing work task, coordination of unmanned aerial vehicle (uav) multiple components in electronic pod working posture, control, remote sensing image sensor,System AT89S52 as the main control chip, expand multi-channel serial and USB interface so as to realize the communication system and peripheral equipment, and design the camera driver module and three dof stepping motor driver module.Through the uav remote sensing experiment proves that the system can satisfy the requirement of remote sensing experiment.

USB extension circuit design

USB extension by CH375 chip implementation.The general interface chip CH375 is the USB bus.Its main characteristic is cheap, convenient interface and high reliability.Support USB - HOST HOST way and way of USB DEVICE/SLAVE DEVICE.CH375 commonly used way of USB host support USB device at full speed, the external need to write the firmware program MCU in accordance with the relevant USB protocol and USB communication.But for common USB Storage devices, CH375 built-in firmware can automatic processing Mass - Storage Mass Storage equipment dedicated communication protocols,Normally, the external microcontroller don't need to write the firmware program. Can directly read and write data from USB storage devices.CH375 and MCU communication there are two ways: parallel and serial mode.USB extension circuit principle diagram as shown in figure 3, CH375 chip set to the built-in firmware mode, use 12 MHz crystal.SCM P0 port connected with the CH375 D0 ~ D7 as a data bus, decoder output connected pieces selected the chip CH375, microcontroller A0 and CH375 A0 is linked together, the choice of CH375 address and data input and output.When A0 to high level is the address of the transmission is D0 ~ D7, low electricity at ordinary times is the data transmission.P3.6 and P3.7 control of CH375 to read and write operation respectively.MCU input CH375, when there are data input through the USB port the interrupt signal, notify the single-chip computer for data processing.When CH375 chip initialization and successfully connected with the master, indicator.

Stepper motor drive circuit

Stable yuntai control three degrees of freedom for stepper motor control, the control of the remote sensing sensor pitch Angle, roll Angle and course Angle to keep stable yuntai horizontal (or vertical) state.Stepping motor driven by THB6128 chip implementation, microcontroller only output step motor running direction and the pulse signal can achieve the goal of control of stepping motor.

THB6128 is high subdivision, special chip two-phase hybrid stepping motor driver output control signal by single chip microcomputer, can design a high performance, multiple subdivision drive circuit.Its characteristics for both bridge MOSFET drive, low on resistance Ron Ω = 0.55, the highest 36 V voltage, large current 2.2 A (peak), A variety of optional segment, up to 128 segments, half with automatic locking function, fast, slow decline, optional hybrid three decay modes, built-in temperature protection and over-current protection.Figure 4 for the heading Angle of stepper motor drive circuit, pitch Angle and roll Angle of the stepper motor driver with the same.Figure in the CP1 and U/D of single chip microcomputer is given respectively drive pulse with the motor running direction of control signal.M1, M2, and M3 for motor drive fine points selection signal input, controlled by the dial the code switch artificially.FDT1 and VREG1 attenuation model respectively to choose voltage and current control voltage input end.When 3.5 V for slow attenuation model;When the attenuation model for mixed;When FDT1 "0.8 V for fast attenuation model. Adjust the voltage of the VREG1 can set stepper motor drive current value.

flight controller hardware structure and circuit1

In the uav flight control system, flight controllers is its core component,It is responsible for the flight control system of signal acquisition, calculation of control law, the posture and speed of the aircraft, and the communication with ground equipment, etc.As uavs become more widely used, its task is becoming more and more complex, and mobility requirements for unmanned aerial vehicle (uav) is becoming more and more high, this request of unmanned aerial vehicle (uav) control core to develop in the direction of high integration and miniaturization.

In a 586 - Engine embedded chip as the core, the design of a certain type of unmanned aerial vehicle (uav) flight controller, system hardware structure is introduced and the corresponding software flow, and the simulation results is presented.

The 586 - Engine main parameters as follows:

• for 32-bit AMD CPU Elan SC520, frequency of 133 MHZ;
• the high performance of floating point arithmetic unit, support complex operations, such as sine, tangent, logarithmic, very suitable for need to the application of complex operations.
• the configuration 512 KB SRAM, 512 KB of Flash, 114 bytes in the internal RAM;
• support 15 external interrupt.A total of seven timer, including internal a programmable timer, provide 3 16-bit internal timer and 3 16 GP timers, plus a software timer.The timer support external event timing and counting.Software timer provides microsecond time hardware benchmark.
• provide 32 programmable I/O, 2 UART.A total of 19 road 12 bit A/D input, including 11 parallel ADC ADC serial input and 8 road, switching frequency is 300 KHZ;No.6 D/A output, including two serial output DAC and four output parallel 12 bit DAC, switching frequency is 200 KHZ.
• working temperature for - 40 ℃ ~ 80 ℃, the size of 91.4 mm&Times;4 mm&Times;7.6 mm.

The type of unmanned aerial vehicle (uav) is to provide communications relay for navy combat troops use medium wheeled unmanned aerial vehicle (uav), the flight controller is a separate packing small airborne electronic equipment,By DC/DC DC power conversion board, the computer motherboard, analog channel plate, the switch quantity of channel plate and steering gear control board,All templates by bus on the motherboard connection, to reduce the size, improve the level of integration.

Detailed below flight controllers of data collection, information transmission and control output, etc.

(1) serial port extension

The figure 1 shows that the flight controller needs with GPS, magnetic heading of communication and radio altimeter, a total of five serial port.586 - Engine motherboard only provide two serial ports, respectively for the use of ground test and measurement and control stations, so the need for a serial port extension.A serial port extension circuit is shown in figure 3.

Serial port extension circuit adopts the TL16C754 UART and four channels - string conversion device, the 8-bit parallel data into serial output 4 road, plus MAX202 and MAX489 level conversion chip, expanded the 2 RS232 serial interface and 2 RS422 serial port, can meet the hardware requirements of flight controller.

• D/A conversion

The uav using simulated steering gear, A total of 6 D/A channel PWM signals to drive the servo.586 - Engine motherboard provides 8 D/A, A total of 4 road 12 parallel D/A (DA7625) were about to rise and fall control steering gear, the aileron servo and the direction of steering gear, 2 road 12 serial D/A (LTC1446) front wheel steering and throttle servo control.Because DA7625 output voltage in the range of 0 ~ 2.5 V, LTC1446 output voltage range of 0 ~ 4.096 V, and steering gear working voltage for - 10 ~ 10 V, so need to signal amplification and translation.D/A level translation circuit as shown in figure 4.

Level by the figure, the D/A conversion principle is adopted in op-amp input addition circuit, the input signal and the reference level proportion together, get the voltage range suitable for sampling.Input level

and the relationship between the output leve

• A/D acquisition

586 - Engine motherboard own 19 road 12 bit A/D interface completely meet the accuracy requirement of the channel number and the transformation of A flight control system, the A/D interface of barometric altimeter data respectively, uav airborne voltage, Engine speed and temperature, the throttle opening and so on.These signals sent to the ground tt&c computer for operators for unmanned aerial vehicle (uav) working state monitoring provides the basis.

• the I/O control

586 - Engine motherboard provides 32 16 programmable digital I/O port, used for acquisition, umbrella compartment open the Engine starting signal, etc., and the output switch signal control and other equipment, take-off and recycling process control of unmanned aerial vehicle (uav).

• power supply module

Flight controller of power supply module circuit for flight controllers provide a clean and stable power supply voltage, used to guarantee the normal work of the flight controllers.Power supply module circuit design is good or not directly affect the flight controller running stability and reliability.Due to the size of the unmanned aerial vehicle has certain requirements, at the same time, considering the reliability and cost, so use in the design of the mature standard module power supply, external work with little or no device.Flight controllers of power supply module circuit is shown in figure 5.

Among them, with 24 t05d12 module power as the main chip of the power supply circuit, provided by the power of 30 w, input voltage range to 18 v ~ 36 v, output power has three road: + 5 v and + 12 v, the power supply for airborne sensors and steering gear.

Made of led light circuit diagram

1,Figure 1 is for capacitance ballast circuit.The C1 Values determine the size of the working current .Working current normally is 12mA-15mA,and Within this scope LED is safe.We can cancel R2,C3 according to the situation .
2, Figure 2 is for the constant current source circuit.The R3 Values determine the size of the working current .When it is 30Ω,the Working current is 12mA.The VT1 voltage at the ends of the collector and emitter=the voltage for the two ends of C2 -The LED pressure drop*N .More the quantity of LED the is , lower VT need resistance to pressure and power.When the quantity of LED the is more ,We can use MJ13001 for VT1.
3, If the quantity of LED the is less ,We can use Figure 1 circuit .While the quantity of LED the is more ,We can use Figure 2 circuit .In terms of cost performance, Figure 2 circuit is the first selection.
4, The quantity of LED the is more ,the higher the energy utilization efficiency is .For example,Working current normally is 15mA(This value not only can make sure the brightness ,but also make sure the LED security)However the quantity is 1 or 90,Electric current is equal because led is In series .The power of the circuit P=220V*1.414*0.015A=4.67W.If 10 LED is used,and the pressure drop is 3.1V,then the power is 10%.While the rest is lost on the ballast or constant current source .But if 90LED is used,then the power will up to 90% .So it’s better to use more LED ,which can increase brightness In proportion,reduce the financial burden on the power part and Increase the reliability.
5, Leds classified two types :concentrated and astigmatism .For the concentrated type,Brightness is concentrated , range is far but it has a halo,which is applicable to the emergency light, flashlight, etc.While for astigmatism type ,Brightness is Scattered and soft,but it own a shorter distance,which is suitable for indoor lighting, desk lamp, etc. (can be mixed with a certain amount of concentrating)
6, There is a trick to choose LED:The bigger Light emitting chip ( visible phosphors in the LED)is ,the brighter the light will be .

PCB design relevant skills

Set skills 
All point design in different stage requires different Settings,
In the layout phase a large lattice can be used in device layout;For big components such as IC, connectors which are not located, we can choose 50 ~ 100 mil lattice accuracy to device layout .While for passive components such as resistance capacitance and inductance,we can choose 25mil.he precision of the large lattice is advantageous to the alignment of the device and the layout beautiful.
PCB layout rules:
1, Normally all components shall be arranged on the the same circuit board side.Only top-level components is too close, some device height is limited and small calorific value device be set up on the bottom ,Such as SMD resistor, SMD capacitors, SMD IC.
2, on the premise of guarantee the electrical performance,elements should be placed on the grid in parallel or vertical alignment in order to be neat, beautiful.In general we don't allow components overlap,but to compact arranged components .Components in the page layout should be uniform distribution, the density is consistent .
3,Different components on printed circuit boards, neighboring,and the minimum distance between solder graphics should be more than 1 mm .
4,The distance from Components to the circuit board edge is generally not less than 2 mm.The best shape for the circuit board is rectangular and aspect ratio is 3:2 or 4:3. When Circuit board face 'is greater than 200 mm by 150 mm, we should consider mechanical strength which circuit board can withstand .
Layout skills
In the layout of the PCB design to we should analyze circuit unit according to the function.Layout all the components of the circuit , we need to comply with the following principles:
1, Arrangement of each functional circuit unit according to the process of the circuit to facilitate signal flow and ss far as possible to maintain the signal consistent direction.
2,Centered on the core of each function unit components, we layout around it .The arrangement of components should be uniform, compact, on the PCB and we should as far as possible reduce and shorten the lead and the connection between each components.
3,For the circuit which works under high frequency , we need to consider the components distribution parameters.Generally components should be as far as possible made parallel arrangement ,which are beautiful, and easy fabrication, easy to mass production .