There’s this belief among my software developer friends that electronics are complicated, hardware is hard, and that you need a degree before you can design anything to do with electricity. They honestly believe that building electronics is more complicated than writing intricate software—that is, the software which powers thousands of people’s lives all around the world. It’s this mentality that confuses me. How can you write all of this incredible software, but a believe a simple 555 timer circuit is complicated?
I wanted to discover where the idea that “hardware is hard” came from and how I could disprove it. I started with something with which almost everyone is familiar, LEGO. I spent my childhood playing with these tiny plastic bricks, building anything my seven-year-old mind could dream up, creating intricate constructions from seemingly simplistic pieces. Much like the way you build LEGO designs, electronic systems are built upon a foundation of simple components.
When you decide to design/build a system, you want to first start by breaking down the system into components and functional sections that are easy to understand. You can use this approach for both digital and analog systems. The example I like use to explain this is a phase-locked loop frequency modulator demodulator/detector, a seemingly complicated device used to decode frequency modulated radio signals. This system sounds like it would be impossible to build, especially for someone who isn’t familiar with electronics. I can recognize that from experience. I remember the first year of my undergraduate studies where my lecturers would place extremely detailed circuit schematics up on a chalkboard and expect us to be able to understand high-level functionality. I recall the panic this induced in a number of my peers and very likely put them off electronics in later years. One of the biggest problems that an electronics instructor faces is teaching complexity without scaring away students.
What many people either don’t realize or aren’t taught is that most systems can be broken down into composite pieces. The PLL FM demodulator breaks into three main elements: the phase detector, a voltage controlled oscillator (VCO) and a loop filter. These smaller pieces, or “building blocks,” can then be separated even further. For example, the loop filter—an element of the circuit used to remove high-frequency—is constructed from a simple combination of resistors, capacitors, and operational amplifiers (see Figure 1).
I’m going to use a bottom-up approach to explain the loop filter segment of this system using simple resistors (R) and capacitors (C). It is this combination of resistors and capacitors allows you to create passive RC filters—circuits which work by allowing only specific frequencies to pass to the output. Figure 2 shows a low-pass filter. This is used to remove high-frequency signals from the output of a circuit. Note: I’m avoiding as much math as possible in this explanation, as you don’t need numerical examples to demonstrate behavior. That can come later! The performance of this RC filter can be improved by adding an amplification stage using an op-amp, as we’ll see next.
Op-amps are a nice example of abstraction in electronics. We don’t normally worry about their internals, much like a CPU or other ICs, and rather treat them like functional boxes with inputs and an output. As you can see in Figure 3, the op-amp is working in a “differential” mode to try to equalize the voltages at its negative and positive terminals. It does this by outputting the difference and feeding it back to the negative terminal via a feedback loop created by the potential divider (voltage divider) at R2 and R3. The differential effect between the op-amp’s two input terminals causes a “boosted” output that is determined by the values of R2 and R3. This amplification, in combination with the low-pass passive filter, creates what’s known as a low-pass active filter.
The low-pass active filter would be one of a number of filtering elements within the loop filter, and we already built up one of the circuit’s three main elements! This example starts to show how behavior is cumulative. As you gain knowledge about fundamental components, you’ll start to understand how more complex systems work. Almost all of electronic systems have this building block format. So, yes, there might be a number of behaviors to understand. But as soon as you learn the fundamentals, you can start to design and build complicated systems of your own!