Articles
SMT (Surface Mounted Technology)
At the early eighties the industry began to replace the traditional through-hole technique with the surface mounted technology (SMT). Special surface mounted devices (SMD) replaced the traditional standard components. SMT although intended in principle for automatic manufacturing only, expand more and more, even into the world of hobbyists. This trend is irreversible and will continue. More and more new components are available in SMD versions only. The SMT technique opens advantages and new applications through miniaturised components and increased reliability. Although an industry standard, most of the SMD components do not have a clear inscription. Due to the tiny size of the components they are labeled with a code. Therefore a correct identification of the components is impossible without appropriate technical documentation. Moreover polarity and pin-outs of different components can not be identified without data sheets. Considering all of these factors SMD is a very tough job for beginners.
The attached manual (downloadable in pdf format) should bring some help and clearness to all newcomers. Moreover it should support service technicians when starting the repair of instruments built with SMD components. The manual includes most of the SMD components that were available until the end of 1998 with their pin-outs and encoding-comparison tables (SMD to classic and vice versa).
SMD does not present a "new technology"; SMD means miniaturisation of existing components requiring new production techniques.
Surface mounted devices (SMD) can be active or passive electronics components but without their well known connecting wires.
In the traditional through-hole technology (THT) the components were placed on the "component side" of the printed circuit board (PCB). The wires of the components were inserted into holes, and soldered to copper pads on the opposite side the "solder side" of the PCB.
SMD components can be placed on one or both sides of the PCB and their metal ends are soldered directly to the copper pads. In such a way, both layers of the PCB could be used as active areas. The thickness of PCBs used for SMD ranges between 0.8 and 1.00 mm. The historical roots of SMD's can be seen in the hybrid circuits based on ceramic substrates (middle of seventies).
Miniaturisation of the SMD does not stop. The distance between the connecting pins is reduced to 0.5 mm (past standard 1.27 mm). The momentary used standard for capacitors and resistors is 0402 (1.0 x 0.5 mm). This 0402 standard requires ten times less area then the 1208 standard and five times less then the 0805 standard.
MicroControllers
Most of us know what a computer looks like. It usually has a keyboard, monitor, CPU (Central Processing Unit), printer, and a mouse. These types of computers, like the Mac or PC, are primarily designed to communicate (or "interface") with humans. Database management, financial analysis, or even word-processing are all accomplished inside the "big box" that contains the CPU, memory, hard drive, etc. The actual "computing", however, takes place within the CPU.
If you think about it, the whole purpose of a monitor, keyboard, mouse, & even the printer is to "connect" the CPU to the outside world.
But did you know that there are computers all around us, running programs & quietly doing calculations, not interacting with humans at all? These computers are in your car, on the Space Shuttle and in all modern instruments.
We call these devices "microcontrollers". Micro because they're small, and controller because they "control" machines, gadgets, whatever. Microcontroller's by definition then, are designed to connect to machines, rather than people. They're cool because, you can build a machine or instrument, write programs to control it and then let it work for you automatically. There are an infinite number of applications for microcontrollers. Your imagination is the only limiting factor! Hundreds (if not thousands) of different variations of microcontrollers are available. Some are programmed once & produced for specific applications, such as controlling your printer. Others are "re-programmable", which means they can be used over and over for different applications.
Microcontrollers are incredibly versatile - the same device may control a printer, a counter, or even your dosemeter.