Adequacy and necessity of circuit design

The circuit design includes two specific working areas, the schematic diagram and the circuit board diagram. These two categories are highly uniform and distinct. It can be done by a professional engineer or divided into 2 professional engineers. The problem solved by the schematic is to grasp the requirements analysis and verify the design. The input is the task book (or derived hardware design requirements) and the hardware design. Its output is a schematic that guides the operation of the board. This work, as its name implies, is the principle of content. The problems solved by the board engineer are closer to reality and can be seen. It is closely related to device characteristics, layout, and board fabrication specifications.

For structural design, most of the structures are closely related to the built-in circuit board, such as: external dimensions, mounting and fixing, external interface, device placement, circuit layout, external radiation, and resistance to external radiation. Many of these factors are not understood by the structural design profession. The most important thing is that in many cases, users are not professional, so our company is forced to have certain hardware research and development capabilities. According to the needs of users, how much to help users in hardware development.

In the actual product design process of this kind of engineering, the author summarizes some personal experiences into two aspects: sufficiency and necessity. These two aspects are closely related to the actual project, and its main purpose is to first ensure that the design meets the requirements, and secondly to ensure that the plan is optimal.

The main meaning of sufficiency is to fully guarantee the design requirements and meet various indicators and performance requirements. The necessity is to consider whether the scheme is optimal and involves cost, processability and maintenance. The two are organically combined, and the designed products are considered qualified.

In addition to meeting customer needs, sufficiency also meets some potential needs. Specifically, it is a reasonable margin and the possibility of future upgrades. This is also very important, and you should avoid future redesigns in order to add an io port. A reasonable margin is difficult to evaluate. For example, the input bandwidth requirement is 5M. Is it reasonable to design 8M or 10M? This is considered by the director and is generally written in the scheme. If a chip, 8M and 20M basically one price, then of course 20M, the margin is big.

The necessity is to look at the design plan in turn, whether it is necessary to design, whether there is a disproportionate cost for a certain demand, etc., and also directly check whether the overall hardware solution is more optimized, whether there is a better solution. If a chip is facing a production stoppage, it is necessary to replace another chip with a better vision in the design. In short, consider it carefully and aim to be far away.

Let me talk about the cost issue, say it is more important, and the cost is also the core content. The more products are bulky, the more you have to consider the cost. I took over a job around 04, and gave me 20,000. I was very happy. I optimized the program of a pic from 4.3K to less than 4K. There is no source program, only code. I didn't understand why I did this. I spent a week, optimized for a while, and finally optimized to 3.7K. The function is completely maintained, and the assembly will be done. Pure statement optimization is fine.

Later, I learned that people are an OEM integrator and don't understand technology at all. The technology they bought, the pic used is 8K capacity, for 4K PIC, can save more than 300,000 a year, I was completely dizzy.

If you say that the virtual one will fall asleep, let’s take a little bit of force:

1: resistance

Note that the power richness should be more than 1 time. Do not calculate 0/8W and use 0805, at least 1206. Otherwise the place on the board may be hot. 1% and 5% have a small difference in price when buying in bulk, and can be tens of blocks in 10 cases, but they are basically negligible. If the board has no other surface mounts, do not select the surface mount resistors, which will result in additional soldering costs. If there are surface mounts, try to use surface mount resistors to save costs, save on welding costs, save space, and have good electrical characteristics.

2: Capacitance

The cost varies widely, and the relationship between the capacitor material and the package is very close. First, the requirements are clearly defined to determine the material and then select the appropriate package. Note that you can fully meet the requirements, because the price varies greatly. The voltage margin of the electrolytic capacitor should be more than double. For example, the 5V circuit must use at least 9V capacitor, because the electrolytic capacitor has poor thermal stability, the temperature is slightly higher, and the withstand voltage drops sharply. The withstand voltage should not be too large. The 5V circuit selects a 35V capacitor, the volume will be much larger, and the price is also quite a lot.

3: peripheral chip

Be sure to check whether the production will be discontinued in the future. You should listen to the opinions and recommendations of the agents or technical support. They are familiar with the product series, but they must distinguish that they may be biased to push a chip. Sometimes it is not necessarily good to use mature chips, such as the classic 6264, the market price is now more than tens of dollars, and often can not buy, and the current 62256 is only 4 yuan.

Do not bother with circuit design, one component and one component are carefully smashed. Say someone is not "scared" big, yes. But we must not say that hardware engineers are not mistaken "out" big.

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