Digital Electronics 2
|Examples for ICs|
|7400, 7403 - 4 NAND|
7408, 7409 - 4 AND
|7404 - 7406 - 4 NOT||7410, 7412 - 3 NAND|
7427 - 3 NOR
|Entrance A||1||Entrances A||1, 2||Entrances A||1, 2, 13|
|Exit A||2||Exit A||3||Exit A||12|
|Entrance B||3||Entrances B||4, 5||Entrances B||3, 4, 5|
|Exit B||4||Exit B||6||Exit B||6|
|Entrance C||5||Entrances C||9, 10||Entrances C||9, 10, 11|
|Exit C||6||Exit C||8||Exit C||8|
|Entrance D||9||Entrances D||12, 13|
|Exit D||8||Exit D||11|
How can the circuits be built up? At that time we used 'breadboards', into which we soldered small plugs. By the way, to do this you'll need a soldering station with temperature regulation. Later we used thick rubber
boards with holes drilled into them. One could produce connections from one hole to the other by using a somewhat more stable wire, without any soldering. There were, at that time, and there are still today, ready to
use experimental boards with plug-in possibilities and internal connections.
Once the first stable connections have been made, one sinks into the world of AND, OR and NOT. Now suddenly, the inversion of a switching state, makes sense. Instead of battling with complicated diagrams, what is
now needed, are clear and concise tables. No half-measures anymore. Each state is now clearly defined.
Of course the internal structure of such an IC 7400 is also shown and explained somewhere, but the good part of the learning process is that one can leave some parts of it out. I have never regretted it afterwards. I
have also, not spent a great deal of time on truth-tables. The wiring diagrams and pin-assignments are the things that I took very seriously. Since generally, a project moves along very quickly until, one comes across an
error, then one can spend days (of one's spare time) looking for it.
As a rule, such an IC has several circuits on-board. From these one picks out one having three connections with AND and OR, and two with NOT. The important thing here is, which is the entrance and which is the exit.
Actually ICs can't handle tension on the exit, however, in my attempts they were pretty robust. After trying out a group of two or three, they were then used for further other circuits.
LEDs are suitable for the display, whereby, the tension must at least, again be halved by using resistances. Resistances can be bought by the box, and straight away, one shows visitors that here an 'electronic
technician' is at work. There are also adjustable resistances or so-called cascades. Indeed, because one would like to build up functioning circuits as quickly as possible, it does make sense to have to have a
selection of all possible sizes. 08/11