Understanding and using oscilloscopes

This article answers a classic question based on personal experience: Why should we develop the habit of using an oscilloscope? The article is written very realistically, and for those who have used an oscilloscope, they may feel that "it is indeed the case." 

The author believes that the oscilloscope is a good helper to link theory with practice, and can help you face the essence of the bug. With the test results of the oscilloscope, "there are pictures and truth", which is convenient for analyzing the problem.

When something right becomes a habit, it has a positive and long-term impact on a person, and it is also of great significance. Developing the habit of using an oscilloscope will also have a lifelong impact on an engineer, and when the habit further rises to a concept, it is not so easy to get rid of it even if you try hard. 

When a product has a problem, many people will subconsciously take a multimeter to measure this and that. The reason is that everyone has one and it is easy to use, so it is popular among engineers. What I want to say here is that this habit is not good. Let me explain the detailed reasons slowly. 

The main use scenarios of multimeters are for simple measurements such as resistance (resistance value, impedance to ground), continuity (whether there is a beep), etc., which are two functions that oscilloscopes cannot do. Voltage values ​​can also be measured with a multimeter. It is more accurate to measure the effective value of voltage with a multimeter, but to observe what the voltage looks like, you still need to use an oscilloscope.

 
There is a classic metaphor that the oscilloscope is the eyes of an electronic engineer. If we don't use an oscilloscope, the product we are developing is equivalent to a black box, and it is difficult to explore its true face. After all, a dark road is not easy to walk. The following is a discussion based on some experiences about why we should develop the habit of using an oscilloscope. 

1. A good helper to link theory with practice 
The oscilloscope is a tool that a hardware test engineer must master proficiently. However, due to the nature of the work, we often have to repeat the test of some fixed items against test cases or specifications, such as various interfaces, internal buses, etc. Over time, many people are not satisfied with this knowledge. The next step for test engineers who are not satisfied with the status quo is to find some information to deeply study the products they are facing, understand the working principle, internal structure, each module circuit, signal flow, etc. Some of this knowledge is clear, some is ambiguous, and some is even incomprehensible. 

When you encounter this situation, an oscilloscope can be a very good helper. For the parts you don't understand, you can first look up the information, try to understand the principle, and then use the oscilloscope to measure the waveform, timing, etc. to verify your analysis results. The oscilloscope can intuitively see the waveform, which will make people feel very clear and impressive, and theoretical knowledge can also be better understood.

 
After measuring all the signals on an electronic product and studying some documents, you will have a thorough understanding of the product you are facing. 

2. Face the essence of the bug 
When we solve the bug, some problems may be solved based on experience without thoroughly understanding the essence. This will lead to hidden dangers, and you may fall into the same trap next time you design a circuit. 

For example, incorrect configuration of I2C pull-up resistors may cause communication failures, and excessive capacitance on the signal line may cause waveform distortion. We may solve the problem by changing the resistance and capacitance values, but this is not enough. If we can see the essence of the waveform through an oscilloscope and then debug, the problem will not occur again in the future, and it will also ensure that some problems that were thought to have been solved at the time will still occur in batches. 

Some EMC problems are caused by the harmonics of internal high-frequency signals. Through oscilloscope debugging, the energy of radiated signals can be effectively reduced while ensuring signal integrity, such as connecting more appropriate matching resistors in series, increasing capacitance to ground, etc. The most direct way to ensure signal integrity is to use an oscilloscope test to avoid overcorrection and hidden dangers. 

3. Pictures speak louder than words 
When some bugs occur, multiple parties need to work together to solve them. Such multi-party email communication requires images as an important basis. I encountered a bug before: there was a probabilistic failure when the host side loaded files to the device side. This involves the hardware and software of three parties, as well as the Taiwan original manufacturers of the host chip and the device chip. After their own inspections and their previous shipping experience, all parties believed that they had no problems. Using an oscilloscope to repeatedly measure the waveform and timing, the problem could not be located at the beginning. (Copyright http://www.diangon.com/) Because at startup, a part of the 1V noise signal will appear on the clock signal line, and then it is determined through experimental means that it is sent by the host side. This is used as evidence to request the Taiwan original manufacturer of the host side to modify it. The reason is that no matter whether this signal affects the communication, at least solve this problem first. After updating the code twice, the 1V noise signal disappeared, and the aging copy machine did not have any problems. 

Out of self-protection instinct and the limitations of knowledge of all parties, each party generally believes that there is no problem on their side. Measuring the waveform with an oscilloscope, finding evidence, and urging modifications will make the problem easier to solve. 

Finally, it is important to note that the operation of the oscilloscope must be correct. Wrong operation and lack of attention to details may turn the oscilloscope into a double-edged sword, causing unnecessary troubles. Special attention should be paid. In actual work, it is often found that different people will get different test results. Here, you need to accumulate more experience. In the final analysis, it is still a question of using it more, and of course, you should also read more documents. 

I hope that engineers can use oscilloscopes more often. At the same time, we also need the generosity of manufacturers to provide more oscilloscopes and create conditions for employees so that they will not develop the habit of using multimeters due to limited resources.