(spunky music)
- Welcome back.
Previously, we talked about why anyone would want to make
a printed circuit board in the first place.
If you're new to designing PCBs,
KiCad is a great starting point,
because it's free and open source.
On this episode, we'll start our 555 badge project,
and create a custom schematic part, also known as a symbol.
If your haven't already, head to kicad-pcb.org
and download the KiCad Software.
Follow whatever installation instructions
are necessary for your operating system.
Once you've installed it, open KiCad,
and you'll be presented with the project manager window.
This is where we can create new KiCad projects,
organize files in those projects,
and launch the various programs
that make up the KiCad suite, like Eeschema and PCBnew.
To start our project, go to file, new project, new project.
I like to create a new folder somewhere,
to keep my KiCad projects together.
So I'll create a new KiCad directory
in the documents folder.
Here, I'll create another folder and name it 555_Badge.
Navigate into that folder
and give your project a name, such as 555_Badge.
A .pro suffix will be added to the end of the file name.
This file is where KiCad
keeps information about your project.
Click Save.
You should see the files in your project on the left,
which at this point, should just be
a blank schematic file, and a blank PCB file.
When you're actually creating a board,
you'll probably jump back and forth between several programs
For example, you might jump right into schematic capture,
realize halfway through that, that you're missing a part.
So you open the library editor, make your symbol,
and then go back to creating your schematic.
Showing this slightly chaotic process
in a video series, is difficult.
So we're going to assume that you've already realized
that you need to make the 555 timer symbol,
and start with the library editor.
Back in the KiCad project manager,
select tools, run library editor.
The library editor program will open with a blank page.
We'll want to create a new component,
so click the create a new component button,
which oddly enough, does not have a menu bar equivalent
under file or edit.
Let's give it the name 7555
and leave the reference designator as U.
Originally, 555 timers were integrated circuits
made with bipolar transistors intended for things
like oscillators and pulse generators.
They were created in the 1970s
and have a sort of cult following
among electrical engineers.
Since then, various derivatives have been made,
including the 7555 timer, which we'll be using.
This works the same as a 555 timer,
but uses CMOS instead of bipolar transistors.
CMOS can operate at lower voltages,
which is how we're able to power our badge project
with a single 3-volt coin cell battery.
But do keep in mind that CMOS
is a little more sensitive to electrostatic discharge,
so just be careful when you're handling the component.
A reference designator, or REFDES for short,
is a combination of letters and numbers,
used to identify electrical components on a board.
If you scroll down the Wikipedia page
for reference designator,
you'll find a list of commonly used REFDES letters.
You'll see that U is used for integrated circuits,
like our 7555, so we'll use that.
Click okay to create our new part.
Before we start editing anything,
let's create a library to house our custom parts.
Click the save current component to new library button,
which looks like a book with blank pages.
Navigate to your project directory,
which should be named something like 555 badge.
When creating components unique to a project like this,
I like to give the library the same name as the project.
So we'll call this one 555_Badge.lib.
Save it, and you'll get a popup,
explaining that the library isn't available
until we load it in Eeschema, which we'll do later.
Note that if you wanted to store your parts
in a larger library that's accessible
by all of your projects, you could do that too.
But for the sake of learning KiCad,
let's keep our parts in a project specific library for now.
The advantage of having a project specific library,
is that it becomes easier to share your custom parts
if you were to upload your project
to say something like GitHub.
Even though we saved our component into a new library,
we need to set that library as our working library.
That will allow us to make edits to our part
and save it back into the library.
It's a little confusing, but it's a necessary step.
Select preferences, component libraries.
Under component library files, click add.
Navigate to your project directory,
which for me, is in documents, KiCad, 555_Badge.
Select the 555_Badge.lib file, and click open.
If you scroll down,
you'll see that the 555 badge library has been added.
Click okay.
Now that KiCad knows where to find our custom library,
we need to set it as our working library.
Click file, current library.
Select the 555 badge library, and click okay.
At the top of the window,
you should see our library file listed.
This means that we have it selected as the working library,
and we can now save any changes
we make to our part, to that library.
Zoom in on the text in the center of the page,
which you can do with the hot buttons,
but I'll use my mouse wheel to make things easier.
Right click on the text.
Because there are two fields here,
you will be asked to select which one you want to edit.
Click field value 7555,
which is the name of our component, and click move.
Move the text down a ways, and click again to place it.
Note that you can hover your mouse over an object
like our REFDES, and press the M key move it,
which I'll be doing often in order to speed things up.
Let's move the U designator up and out of the way for now.
Click the add pins button,
and click somewhere on the page to create a pin.
This is where it can be handy
to look at the datasheet for our part.
At the bottom of the first page,
we see the 8-pin DIP package, with pin names and numbers.
Pin names give a description of what that pin does.
And pin numbers are used to designate
where the pin is on the physical part.
Notice that on our DIP package,
the numbering starts with one to the left of the notch,
and counts up going down.
Pin five is across from pin four.
And the numbering continues going up on the opposite side.
We see that pin one is ground, pin two is trigger.
And notice the horizontal bar over the pin name.
This means that the pin is active low,
and it can be useful to keep that bar on the pin name
when looking at schematics,
so we'll replicate it on our part.
You can choose to make the schematic symbol
look like the part here, but it doesn't ultimately matter.
The important thing is that
the pin names and numbers match up.
Putting the datasheet and library editor side by side
can be very helpful here.
Back in our library editor,
name the pin GND and assign it the number one.
Don't worry about orientation, we'll fix that in a minute.
The electrical type is really only useful
if we're doing an electrical rules check,
once we've made the schematic.
Most of the time, I find setting up this check
to be more trouble than it's worth,
so we can just ignore the type for now.
Click okay.
Click again anywhere in the sheet to place the pin.
Because we're still in the add pin mode,
we can just click on an empty area in the sheet
to create another pin.
Name this ~TRIG, in all capital letters.
Note that the tilde gives it
the horizontal bar over the name.
Give it the number two.
Click okay, and click again to drop the pin.
Repeat this process for the other six pins,
where OUT is pin three, ~RST is pin four,
CV is pin five, THRESH is pin six,
DIS is pin seven, and VDD is pin eight.
Our pulsing LED circuit is based
on a simple 555 timer flashing circuit,
like this one from 555-timer-circuits.com.
Notice that the pins on the 555 symbol
aren't ordered by number.
Instead, they're configured in a way
that makes reading the schematic easier,
with power and ground pins on the top and bottom,
the output on the right, and everything else on the left.
We want to organize the pins
to line up with the pins on the example circuit symbol.
Right click on pin one, and select rotate pin to spin it.
Do this once to have the pin face down,
just like in the example circuit.
Right click on it again, and select move pin.
Place this pin down and over from the middle line
by one grid dot.
Hover over pin five with your mouse
and press the M key to move it.
While the pin is on your cursor,
you can press the R key to rotate it.
Move and rotate the pin
so that it is next to the ground pin,
but to the right of the middle line by one grid dot.
I like to keep pins
at least two grid spaces away from each other
to allow the text to be easily read.
Continue moving the pins around until they are organized
the same way as in our example circuit.
If you need help remembering the hotkeys, press the ? key,
and that'll bring up a list for you.
While this is a perfectly usable schematic symbol,
we should probably draw a box around it
to make it look nice.
Click the draw rectangle tool,
and draw a box around the pin names,
but just touching the inside of the pins.
Notice that the origin of our grid
is shown by the two intersecting blue lines.
When we go to place the part
in the schematic capture program,
the part will be attached to our cursor
at this origin point.
And it will also rotate around this origin point.
Right now the origin is in the center of our part,
which is a good spot.
If yours is not, you can click the anchor tool,
and click in the middle of the part to move the origin.
We can tighten up our symbol
by moving the REFDES to the top left of the symbols box,
and the part name to the bottom right.
There's no real standard
as to where these pieces of text should be,
but I like to try to keep custom parts
with the REFDES on top and name on the bottom.
And that's it!
We just made our first schematic symbol.
Click file, save current library.
You'll be asked if you want to include
the latest component changes.
Click yes, and click yes again to modify the library file.
Go ahead and close out of the library editor.
Now that you've seen
how to create your own schematic symbol,
we're ready to make the full schematic.
The good news is that
we don't have to create a custom part for everything.
There are libraries maintained
by KiCad, Digi-Key, and others,
that make our lives a lot easier.
But knowing how to make your own part is very useful
for when you need something
that's not in one of those libraries.
On the next episode,
we'll see how to connect our 7555 timer
to other parts that are found in those libraries.
See you then.
(spunky music)