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D intelligent hardware development lecture

by:Rigao      2020-05-08
With simple language and complicated technology, novice hardware engineers are doing odd jobs in the company: looking at pictures, repairing boards, and maintaining materials. Although it is just a handyman, there is generally no idea for newcomers to work. When the 'smart' editor used to bring newcomers, he threw them a faulty circuit board to analyze. The newcomers looked at the circuit boards of hundreds of components and dozens of pages of schematic diagrams, and immediately caught them, I don't know where to start. Hundreds of devices, dozens of pages of schematic diagrams, analysis of faults is not easy, today pick a simple, take the MCU as an example, to talk about the four basic ideas of hardware engineers to analyze the fault board: STM32 single chip microcomputer system does not start up. First, figure out the startup process of the single chip microcomputer, then check which part of the reason in sections, then judge the specific reason by measuring the difference between good and bad circuit boards, and finally verify the reason through cross exchange. All MCU boot processes are similar: external power supply--> System Reset--> Crystal oscillator provides clock--> Press the power button--> The system runs. In the same way, when analyzing other problems, you should first understand the workflow, and then start analyzing. You can't blindly think about where to see. The process of MCU startup has been described above, so it is necessary to check the problem one by one according to the process to see where the problem is. First look at the chip welding, whether there is obvious offset or virtual welding, then look at the external power supply, measure whether there is voltage, then look at the reset, the microcontroller is generally Power-on reset, no tube, however, many Bluetooth MCU or peripheral coprocessors will have a reset pin, depending on whether the level of this pin is normal. Let's look at the clock again. If the chip is well welded and the power-on and reset are normal, the crystal oscillator should have output. After pressing the power button, the system runs and can see regular current changes. After the program in the chip starts to run, you can see where it is running through the Log information. If the MCU circuit board is not turned on, the whole chain will have problems: the chip is not well soldered, the power supply voltage is wrong, the Crystal does not vibrate, and the program runs. Segmented troubleshooting can narrow the cause of the fault to a small range and find problems faster. Every paragraph should be a bad contrast. Measure the relevant data of a good circuit board and compare it with a bad circuit board. For example, if it is suspected that the crystal oscillator output is wrong, then look at the circuit board that can work normally, what frequency, what amplitude, and what shape waveform the crystal oscillator output is. If the waveform of the fault board is consistent, it is not a problem of crystal oscillator. If the waveform is obviously different, the reason is found. If it is found to be a certain section of the problem after measurement, you can take the good circuit board and the bad one to do the cross exchange of components. For example, if the measured crystal oscillator output is wrong, is the crystal oscillator itself broken? You can change the crystal oscillator to see if the phenomenon of not starting up follows the crystal oscillator. If not, it is necessary to suspect the circuits around the crystal oscillator, such as the starting capacitor and MCU itself, which can also be verified by cross exchange. Hardware circuit failure, the analysis idea is right, it is easy to find the reason.
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