by AdamStanislav - uploaded on October 20, 2017, 7:29 pm
This is a 28-pin (or 28-lead) dual in-line package (also called DIP28). The image keeps the actual proportions of a DIP28, such as the ATmega microcontrollers used in the very popular Arduino Uno tool (used to teach/learn electronics design, see https://www.arduino.cc for more details, as it is quite fascinating to electronics newbies).
The DIP28 is very small. If your computer knows the correct DPI of your monitor, setting the width of this particular SVG to 8 mm and its height to 35 mm will show you its real size. Indeed, the numbers I used inside the SVG code are all in µm (micrometers, there are 1000 µm in 1 mm).
Anyway, the pins (or leads) are all numbered. When looking at a schematic you can usually see the numbers listed, though not necessarily in the right place. The numbers do not appear on the DIP itself (would be too small anyway). You are supposed to know the numbers by holding the chip with the notch facing to the top (as in this image). The top left pin is pin 1, the one below it pin 2, etc. Once you count to the bottom, the next pin number starts at the bottom right and the numbers move upward from there.
So, in a DIP28, the top left is pin 1, the bottom left pin 14, the bottom right pin 15, and the top right pin 28. See https://en.wikipedia.org/wiki/Dual_in-line_package#Orientation_and_lead_numbering if this is confusing.