This post summarizes the content of a book that aims to make the embedded field easier to understand by covering topics such as Fourier transforms, analog and digital signals, and basic circuit theory.
It explains the characteristics and operating principles of components such as resistors, capacitors, inductors, and transistors, and introduces concepts like pull-up, pull-down, and open collector.
It can help you gain foundational knowledge necessary for designing and understanding embedded systems, and understand the roles and interactions of electronic circuit components.
I majored in Electronic Engineering, but during my undergraduate years, I just took courses to get good grades without thinking about the meaning or necessity of each subject. Naturally, after the semester ended and the holidays passed, nothing remained in my mind… ㅜ_ㅜ
I found this book while searching for information on embedded systems, and after skimming through it, I found it to be very well-structured. It explains the difficult field of embedded systems in a very light way, but the content itself feels substantial.
This time, I want to put some knowledge into my head, so I'm going to organize the contents of the book in a blog post!!!
All signals can be represented as a sum of Cos or Sin!! → Ultimately, it separates the signal by frequency.
For example, with a square function,
From a frequency perspective of the square function, it becomes a sinc function. This means that the square function is composed of a continuous combination of numerous sine waves, and the amplitude and period of the sine waves around frequency 0 are long, while the amplitude and period of distant sine waves are short.
By looking at it from a frequency perspective like this, we can check how many frequencies a single signal is composed of, and we can analyze the magnitude and amplitude of each signal.
If you go to this site, you can understand Fourier Transform a little easier!!! (It's good to change it to a square wave and see!)
2. Analog Signal & Digital Signal & Ground
Analog signals are usually composed of AC and DC (alternating current and direct current) components,ACis a signal with changing polarity, and DCrepresents a steady state. In part 1, we learned that all signals can be created by adding multiple signals with different frequencies. In other words,All analog signals can be created by adding multiple frequency components.
Digital signals are mostly composed of DC components. That is, digital signals are also a type of analog signal. However, a certain threshold value is set, and if it is above that value, it is considered High, and if it is below that value, it is considered Low.
When a digital signal changes from 0 → 1 or 1 → 0, it changes while causing a bounce, and this part can cause problems in digital systems (the voltage may be lower, or a recognition error may occur). Therefore, the design should consider this aspect.
GND = GROUND represents the reference 0V and can also mean the negative terminal of a battery. GND is the point where all currents converge and serves as a reference point for distinguishing between 0 and 1.
3. Very Simple Circuit Theory
Resistor : A resistor can limit the amount of current flowing through a circuit! When passing through a resistor, the voltage drops by the resistor x current value. Expressed as a formula, it's V=IR
Capacitor : A capacitor is a device that allows AC components to pass through but blocks DC components. In other words, it acts as a resistor with different values depending on the frequency of the AC and DC components. dV/dt = I / C, meaning the higher the rate of change of voltage over time, the better it passes through and the lower the resistance. If the value of C increases, the current increases!!
Another property is that it can charge and discharge current.
Inductor : An inductor prevents the current from changing. V = L dI/dt, meaning only low-frequency currents pass through. This means it can be said to block the rapid flow of signals. In other words, the larger the L, the smaller the current!!
To summarize, for a certain desired voltage, the amount of current can be controlled,
For R, the larger the R, the less current flows, For C, the smaller the C, the less current flows, For L, the larger the L, the less current flows.
From a frequency perspective, for given RLC values, R is not affected by frequency, C has lower resistance at higher frequencies (more current flows), L has higher resistance at higher frequencies (current flow is difficult).
Filter!
Low Pass Filter (LPF): A filter that allows only low-frequency components to pass through. It is often used because noise is usually a high-frequency component.
Since a capacitor does not allow DC to pass through, it becomes an open circuit. That is, VinDC = DoutDC
When a capacitor allows AC to pass through, it becomes a short circuit. Here, the value of the current flowing changes depending on the resistance value of R. Therefore, to reduce the current flow, i.e., heat generation, the size of the R component can be increased.
Transistor
The purpose of a transistor is to be a device that allows you to control the current freely!
B is called the base, E is called the emitter, and C is called the collector. When the switch is turned on by B, it connects E-C to allow current to flow, and otherwise, it cuts it off. The question of how the amount of current flowing is determined is based on how much voltage is applied between B-E!!
Depending on the amount of voltage applied to the base, saturation region, active region, and cutoff region are created. Active region: The region where the current between C-E changes significantly due to the input to B! Cutoff region: The region where the voltage of B is too low and no current flows between C-E! Saturation region: The region where the voltage of B is too high and no more current flows between C-E!
The two functions of the transistor come from here: amplification and switching!
Switching is expressed using the cutoff region and the saturation region,
and amplification can be expressed using the active region.
4. Pull up, Pull down, & Open Collector
Low Active is indicated by CS(chip select)_, /, etc., and means it operates at a low voltage. Conversely, High Active means it operates at a high voltage (1).
As shown in the figure, if the Digital Chip is a large resistor, in Low Active, Pull up means that when the switch is turned on, a 0 value is applied to the Digital Chip, and Pull down means that when the switch is turned off, a high value is applied to the chip. In High Active, it's the opposite!!
Pull up & Pull down can be said to be operations that change depending on what the default level value is set to. In the real world, if a chip is like the example above, even a small static electricity can cause the motor to operate. If that motor is a cannon, that would be a huge problem.
Transistors play the same role as pull up & pull down.