Because I’m kind of a nut for all this electronics stuff, I have a few old PCI cards sitting next to my desk as office decoration. One of them is a 4MB VGA graphics card from ~15 years ago. Another is a 10/100 ethernet card from roughly the same vintage. They are useless today, but they look cool, and are pieces of history. While looking at one of them, I thought it might be interesting to explain what all the little pieces on them do. Computer PCI cards are often pretty sparse for visible components though, so to facilitate this article, I’m including a picture of a breadboard I had at home. It’s kind of a mess, because I was experimenting with several things all at once, but there are basically two circuits. One is a boost converter (tucked away on the left side) and more towards the center is a 555 timer circuit.
This is a much better example of components that are easily visible. You can see their shapes clearly and I can do a much better job explaining how everything works because I built it, but the same components work basically the same way on any hardware, including my PCI cards.
Click image for a full-size view.
- First we have a black rectangle with metal legs coming out of it on either side. This is a 555 timer IC (integrated circuit). This particular packaging of the chip is called DIP (dual inline package). There are other packages like SMT (surface mount technology) that can result in a smaller physical footprint, but they are much harder to use on breadboards or by hobbyists who can only use their hands. This is the same 555 chip I mentioned two weeks ago in my turn signals article. I’m not doing anything fancy with it here. It’s just configured to generate pulses to drive an LED.
- This isn’t super visible here, but it’s a black package, with a metal back and 3 metal legs. It’s an LM317. This chip is a simple linear voltage regulator. It’s used to drop voltage to an adjustable value efficiently and easily. When dropping voltage like that in a circuit, heat may need to be dissipated. The LM317 has a metal back so that a small (or large) heat sink can be attached.
- There are actually 6 of these visible on the board. This one is an electrolytic capacitor. It stores charge and then can release it very quickly. Capacitors are often used for buffering choppy signals (among many other things) or providing a more continuous voltage when output may drop for very brief periods. There are two capacitors on the lower left that are doing exactly this. The boost converter circuit outputs an inconsistent voltage if a load is connected drawing power. The capacitors help buffer this while the circuit has time to charge up again and deliver another pulse. This all happens very rapidly so the output appears relatively constant. There is also a ceramic capacitor on the board as well. The tiny blue thing above the 555 IC is also a capacitor.
- This semi-circle black plastic component has 3 metal legs beneath it. It is a transistor. I could write several articles about transistors and their many, many uses. They can be used as electronic switches, amplifiers, drivers, and countless other things. In this circuit I was using it as a simple LED driver. This isn’t really necessary to run an LED, but it was a helpful exercise in learning how to calculate the transistor circuit that I needed to use.
- This black cylinder is a diode. A diode is a device that only lets current pass through in one direction. Usually the direction is indicated by one end being a different color. In this case, it’s the silver cap on the lower side. This particular diode is called a Schottky diode and is characterized by a low forward voltage drop. Generally about half that of a standard silicon or germanium diode. All diodes will cause a drop in voltage because of how they are constructed, but sometimes it’s necessary to have as little drop as possible, as is the case in my boost converter circuit here.
- This metal donut with a coil of wire around it is a toroidal inductor. Inductors come in many shapes and configurations (some look just like electrolytic capacitors). An inductor is also an energy storage device, like a capacitor, except instead of storing charge directly, it stores energy in a magnetic field. When the magnetic field is allowed to collapse, a current is generated. This allows for a different kind of circuit buffering. Here, it’s being used as an integral part of the boost converter circuit.
- Tucked underneath the inductor is a MAX757 switching voltage regulator IC. This is brains of the whole boosting process. Essentially it provides the fast switching necessary to boost a voltage signal higher than the input. For example, with my setup here, I can take a voltage as low as 0.7VDC and based on how I have the circuit built around the MAX757, it will boost it up to 5VDC. It will actually accept any voltage between 0.7VDC and approximately 4VDC and produce a fairly smooth 5VDC output. Some switching voltage regulators (like the MAX757) are adjustable, meaning by configuring circuit values around the regulator, you can change the output. In my case, the output voltage is controlled by a simple resistance divider. By swapping in a different resistor value, I can change the output from 5VDC to 3.3VDC. These switching regulators can also be used to reduce voltage, just like the LM317, except they are more efficient because the extra energy isn’t converted to heat.
Hopefully this was an interesting explanation of a range of components. It’s certainly a lot to cram into a short article!