Some electronics basics.

If you have a background on electronics you can skip this whole section since I would do nothing but bore you.

The idea behind this, is trying to introduce people who have little/no background on the assembly process of a relative simple electronics circuit. Please keep in mind this is a mere flash trip into a huge and complex turf, if you are really interested on it, get into a real class or buy some real books on the matter.

This is not a great place to learn things the right way, but fair enough to get our task done. This is NOT intended to be a crash course on electronics.

So you still want to build a Freewing IF, right?

Schematic diagrams.

The IF is built from several TTL ICs which we need to wire so they acomplish the task we want. Electronics schematic diagrams tell us the way that wiring has to be done in order for a circuit to work. On schematic diagrams we use symbols to represent ICs, capacitors, resistors, diodes etc., and wiring among them (yes, a PCB job is nothing more than conduct from an IC's pin to wherever it may be tied).

Now let's see what these symbols are for par_sche.gif from Freewing.

VCC

Signals noted like this point have to be tied to our main circuit VCC.


Gnd

Signals noted like this point have to be tied to our main circuit ground.


Polarized Capacitors

Polarized caps are noted like this. Attention must be payed when connecting theses to match noted polarity.


Non polarized Capacitors

non polarized caps. This can be connected anyway regardless of polarity.


7805 - Voltage regulator

This will be our power suply regulator.

Converts from 7- 9VDC to our required TTL 5.0 VDC.

7805 pinout.


Diodes.

we'll use 4 of these to convert from ACto DC on our power supply module. The ring position cooesponds to where the arrow points to.


Transformer.

Pay attention to which is the 120 or 240 AC side and which is the 8-9 AC side.


74HC14

Hex Inverting Schmitt trigger.

A 74HC14 has 6 of these gates inside.

  in out
Gate A 1 2
Gate B 3 4
Gate C 5 6
Gate D 9 8
Gate E 11 10
Gate F 13 12

Vcc - Pin 14, Gnd - Pin 7.


74HC74

Dual D type Flip-Flop.

Each 74HC74 has 2 of these combo gates. Vcc - Pin 14, Gnd - Pin 7.


74HC157

Quad 2-input multiplexer.

Vcc pin 16, gnd pin 8.


74HC573

Octal D-type Latch

Vcc pin 20, gnd pin 10.


74HC574

Octal D-Type Flip-Flop

Vcc pin 20, gnd pin 10.


So What goes where?

On an schematic diagram we use lines to represent connections between two points.

When a line crosses another and there is no connection we note it like this....

line over a line.

line over a buss.

On the other hand if a line makes a connection to another we note it like....


Busses

Now, imagine we wanted to "throw" 8, 16 or more lines from an IC to another IC. hmmmmmm..... that would get us into a real mess to trace something on our schematic, so what we usually do in these cases is we use "busses".

Busses are just like connection lines in the sense they also tell us where connections lead to, but busses carry several lines "inside" of them. Busses are represented by thick lines. A buss acts like an imaginary "sleeve" over your lines, you just have to draw line into a buss to note that lead should be followed the other side of the buss. How you ask? Simple. We have a name for every signal our circuit handles. Then, We simply note that name on the line before we "tie" that signal to any buss. I Know, I Know... it sounds much more complicated than in real life. for example.

Numbers on the left represent the pin number of the DB25 that plugs into the PC, Next we get The Pin Name, then the name Freewing designated for that signal inparticular.

Note how signals labeled I7, O1, O2 and O3 are not integrated to the buss. they simple cross it making no connection.

If we trace that buss on our par_schem.gif we'll find this:

part of 74HC157 "alias" U002 on our circuit.

Now we know where each pin gets connected to. For example::

Pin 15 Labeled /ERROR from the DB25 will connect to Pin 4 of U002.

One final word of caution.

Some schematic diagrams do not note where Vcc and gnd should be fed to each of the ICs since this is sometimes obvious. In our case par_sche.gif does not. So always remember to connect your IC to Vcc and gnd or your Circuit will not work

See? You knew all off this!

OK. guess this is about it.