After a period of hard study, I finally made a PCB board of my own design. The feeling after finishing it is completely different from the feeling before making it. The board I made is actually very simple. It is an 89C52 microcontroller in an LQFP-44 package, a CH340X USB program download chip, a micro USB socket female header, an L298 motor driver chip, and a few wiring terminals. That's about it. That’s a lot of stuff. Let me show you some pictures of these things first! Then let’s talk about the pitfalls I encountered.
The markings on this port have been physically tested by me, and there should be no errors. If there is any hope, please remind me in time.
I only looked at the left half of this circuit diagram. My schematic is as follows.
The problem with this schematic is that the micro usb and CH340X GND are not connected together.
Okay, basically all the required components are displayed! Let’s talk about the problems encountered. The first is the problem of L298 heating after power is supplied. After analysis, it may be because both signals are connected. The initial state of the microcontroller should be high level, which means that L298 is both conductive. It was connected, so it caused a short circuit. I need to pay attention to this problem next time. At least use a switch at the power supply. I can't make L298 work before writing a program. After I cut a few wires with a scalpel, the short circuit problem disappeared. .
The second question is the 51 microcontroller. For those who have no experience, I suggest that you just make a component with the smallest system first. Lead out all the pins and get a pin, so that you can fully understand the microcontroller. Don’t be like I just want to make the finished product directly, which is impossible. Fortunately, my pins are marked correctly. I downloaded the program and tested P0 to P4 without any problems. If the P0 port is used, remember to add a pull-up resistor, otherwise It doesn't work. I haven't tested how to use the P4.5 port. When I turn on the light, it doesn't light up. I left a via hole when I removed the chip. The via hole at that time was 45mil, which felt a bit big. Next time, the via hole should be set to 0.6mm. It takes up less space and a pin can fit in just right to avoid poor pin contact. If the space allows, place the vias before the chip is out. This way, it is easier to measure whether the chip pins are soldered well. You don’t have to look at the picture while looking for test points. The efficiency is too low, because you have to manually solder so many pins yourself. It is difficult to ensure that there is no false soldering, so we have to measure it again to ensure that it is foolproof. Also, the program under the 51 board needs to be powered on again. Next time, I need to install a switch. It will be much more convenient to just cut off the power of 51. I forgot about this during the design.
Let’s talk about the ch340x chip. This chip is really too small. Sometimes you don’t have an overall understanding just by looking at the size. I suggest friends who are not good welders not to solder this chip manually. I can’t see clearly with my bad eyes. That’s it. Well, there is another mistake, that is, the Micro Usb package is drawn wrong, which leads to one of the connections to the 340 being wrong. It requires secant soldering of flying wires. I really can’t solder this without any skills, so I just soldered it reluctantly. On. Let’s take a look at my changes!
The package diagram of this Micro Usb is wrong. One of the wires is connected wrongly, so I have no choice but to fly it. Although the USB socket was drawn wrong, it was barely welded on and it worked. I’ll make more of it next time! I finished the drawing without checking it at all, which caused many problems later.
This is the first time I have designed a board by myself, and I am a little anxious, so I have brought a lot of problems to myself. Next time I have to check it carefully and don’t dig a hole for myself!