(fast paced music)
- On the last episode,
we created a schematic symbol for our 555 badge project.
This time we'll be using that symbol and connecting it
to parts we find in other libraries to make out full circuit
This is an important step in the board creating process
as we need to tell KiCad how our components
are connected together.
Schematic capture also known as schematic entry
is the process by which the designer, us in this case,
creates the circuit diagram in the Cad program.
We'll be using KiCad's EE Schema for this part.
Often, PCB layup programs aren't really good
at helping you design circuits but some are starting
to include simulation programs also known as SPICE programs.
While we're glossing over the whole circuit design part,
our fading LED circuit was based on a flashing LED example
from 555 timercircuits.com.
This program is LT-SPICE.
A free circuit simulation program.
A transistor was added to allow more current
to flow through two LEDs
and a large 100 microfarad capacitor
was connected to the transistor's base.
This causes the voltage on the positive side
of the capacitor to now slowly rise and fall
which in turn means a slow increase and decrease
of current flowing into the transistor's base.
If we run the simulation and measure
the current flowing through the LEDs,
we can see how they will, in theory,
slowly increase and decrease in brightness.
I won't go into the details of using LT-SPICE
but if you're curious, Sparkfun has a very good
tutorial on getting started with it.
Once the circuit has been simulated,
I like to build it on a bread board to make sure
everything works in reality.
Sometimes, the simulator doesn't catch all the little
variations in parts, capacitors and wires and so on.
Here, we're see the LEDs fading as expected.
Now that we've proven that the circuit works,
I like to re-draw it on some engineering paper
to organize the parts in a way that's easy to read
before entering into EE Schema.
Open KiCard and you'll be greeted
by the familiar project manager window.
Click tools run EE schema
to start the schematic capture program.
You should see a red colored border with numbers and letters
On very complex schematics,
it can be handy to refer to sections.
For example you might say there's an issue
with the filter design in b4
and other engineers could locate that section easily.
The bottom right contains some fields
that provide information about the schematic
which can be very helpful if you have several pages
or different versions printed out on your desk.
It's always a good idea to fill this part out
in case you ever want to share your schematic
or keep track of changes.
To do that go to file,
page settings.
In the window that pops up, click the three arrow button
to copy today's date into the date field.
You can use whatever versioning system you like
but I like to use a simple incrementing numbering system.
So I'll write v01 here.
I'll write the same v01 on the PCB somewhere
so I know that it's based on this particular schematic.
If I ever make changes to the hardware,
I'll change the schematic in PCB to V02 then V03 and so on.
We'll write the title as 5 5 5 badge
and leave the company line blank.
The comment lines are a good way to write things
like the author and license.
For some reason the comment lines appear backwards
so we'll write author your name in the fourth comment line.
We want people to be able to use this board
for other purposes so we'll have it be open source
under the Creative Commons license.
write license cc-by 4.0 in the third line
and creativecommons.org slash licenses slash bi slash 4.0
slash in the second.
Click OK and you should see the title block
filled out with your information.
Click place component to go into the place component mode.
Notice that your cursor changes to a sort of pen symbol.
Click anywhere in the schematic sheet
to open the part chooser.
Expand our custom 555 badge library, select 7555
and you should see the symbol that we created
in the last episode up here.
Click OK and the symbol should appear on your cursor.
Click somewhere in the middle of the schematic sheet
to drop the component.
As in the library editor you can hover your mouse
over the part and press the M key to move the part.
With the part on your cursor, you can press R to rotate it.
You can click to place the component in a new location
or press the Escape key to cancel.
Instead of using the place drop down menu
to pick a part every time,
you can also click the place component button on the right
or just press the A key to bring up the component chooser.
Let's go ahead and add all of our resistors.
In addition to our 555 badge library that we made,
you can also browse through all of the libraries
that come default with KiCad.
These have some very useful components
so it can be handy to look through here first.
Expand the device library, scroll down and click on R.
This is our basic resistor component in KiCad.
Click OK.
Click to place the first resistor above
and to the left of the discharge pin.
Click again to bring up the component chooser window.
Remember, we're still in the place component mode.
R should already be selected since it was the last component
we chose so just click OK or press Enter.
Place this resistor a few grid marks down from the first one
Click again.
Make sure R is selected and click OK to get a third resistor
With the resistor on your cursor,
press the R key to rotate it.
With this resistor horizontal,
place it down into the right of the out pin.
My goal is to place all of the components
in the general area of where they need to go
based on my hand-drawn schematic.
Usually I'll have this schematic on my desk
so I can reference it easily but that's a little hard to do
with this screen capture program so I'll just overlay
a picture of it so you can reference it too.
Continue placing all seven resistors.
Don't worry about exact placement.
We can fix that later.
These are great generic resistors
but it can be handy to show their values.
Hover over the first resistor and right-click.
If you're asked to choose between a field value
and component, select the component.
In the pop-up menu select edit component and value.
Where it says text replace R with the value of our resistor
which is 22K in this case.
Don't worry about adding the ohm symbol.
Most schematics assume the units for resistors.
Click OK.
A faster way of doing this is to hover your mouse
over the resistor and press the V key for value.
Do this for the second resistor
and change its value to 330K.
Repeat this process for the rest of the resistors
referring to the example circuit diagram for resistor values
Once you're done, press the A key
to bring up our part chooser again.
We want to add our two capacitors next.
Instead of trying to browse through all
the components in the library,
we can also use the search function to make life easier.
Type C in the filter and you should see
a selection of capacitors appear.
C is a regular unpolarized capacitor but we don't want that.
Our 10 and 100 micro farad values will be too big
for most ceramic type capacitors so we'll rely on polarized
electrolytic capacitors which means we'll want to show
that they're polarized in the schematic.
CP means capacitor polarized.
KiCad's default is to have the positive bar of the capacitor
be hollow but I'm not a fan of that look.
The curved negative bar is what I learned in school
so I'll go with that.
It's really a matter of personal preference
as to how you want your schematic to look
so choose whichever you like.
I'll place the first capacitor just below the 330k resistor.
Note that the positive side should be facing up
as we'll connect the negative side to ground eventually.
Place a second capacitor in parallel with the 100k resistor
Give the first capacitor a value of 10 microfarads
and the second a value of 100 microfarads.
All components that have some kind of value
and aren't resistors should have the units shown
which is why we write an F for the capacitors.
Press A to open the component chooser and search for LED.
Select the first LED option and press OK.
Rotate it so that the current will flow down through the LED
and place it below one of the 100 ohm resistors.
Because the LED symbol shows that it's an LED
and not just a diode, thanks to the little arrows,
having led as the value is a little redundant.
It's often helpful to change the value
to the color of the LED we want.
So press V over the LED and change the text from led to red
You can also copy components so that you can keep the value
and other attributes you might have assigned.
Hover your mouse over the LED and press the C key.
A new LED will appear on your cursor.
Click to place it below the other 100 ohm resistor.
Press A to open the component chooser.
We want to transistor but here's the tricky part.
Depending on the type and manufacturer
some of the pins might be swapped.
So we need to know what transistor we want to use
before putting one in our schematic.
The 2N3 904 is a very common and very cheap NPN bipolar
Junction transistor that will work
just fine with our circuit.
If we look at the data sheet we can note that the pins go
emitter base collector with the flat edge facing up.
Back in our component chooser, we can search for 2N3 904
and see that the pins line up with the one
from the datasheet emitter base collector.
Select it and click OK and place it so that the base lines
up with the 10k resistor.
We're almost done but there's a slight problem.
KiCad doesn't have a battery holder or slide switch
that we need for our board.
The good news is that Digi-key has it in their KiCad
library so let's go download that.
This is another example of where that messy, chaotic nature
of board layout comes into play.
You'll be going along making your schematic and then say,
realize that KiCad didn't have the part you need
in the default library so you either consider
making your own or you start going through third-party
libraries all the while checking Digi-key site
to see if they have the part you need in stock.
To keep these videos rolling, let's assume for now
that you've already identified the specific battery holder
and switch that you need.
Head to github.com slash digi-key slash digi-key
dash KiCad dash library.
Click clone or download and click download zip.
Find where you downloaded that file and unzip it.
Go into that folder and copy the digi-key
KiCad library master directory.
Go to where you're keeping your KiCad project files
which is documents KiCad for me.
Create a new folder called libraries.
This is a good place to keep libraries
that we download from the internet
or any larger custom libraries we might make
for sharing among projects.
Paste the digi-key library directory in there.
If you navigate into digi-keys library folder,
you'll see that it's made up of a symbols directory
which is a collection of schematic symbol libraries
and a dot pretty folder which is a library
for a lot of footprints in KiCad.
Back in EE schema we need to import the digi-key
library that we just downloaded.
Click preferences component libraries.
In the component library files section click add.
Navigate to the key symbols folder in your KiCad library's
directory and select DK battery holders clips contacts
and click open.
Click add again, navigate to the digi-key symbols folder,
select DK slide switches and click OK.
Scroll down in the library files section
to verify that both libraries were added.
Click OK.
Press A to add a component.
Scroll down and you'll see that both digi-key libraries
were added as DK batteries holders clips contacts
and DK slide switches.
Expand the battery library, select BS 7
which is the coin cell battery holder we'll be using
and click OK.
Rotate it so that the positive pin is facing up
and place the part to the left of the 330k resistor.
Press A again and expand the DK slide switches library.
Select the eg 1218.
This is the three terminal single-pole
double-throw switch that we'll use.
Click OK.
Rotate it so that pin 3 is facing down
and place the part just above the battery symbol.
We could wire everything up now
to make our completed schematic but something that
makes things easier to read is flags.
Flags have the effect of connecting things together
without having to look at wires on the screen.
It just makes things cleaner.
Any node that has a flag with a name is automatically
connected to all other nodes with that same flag and name.
Most commonly you'll see power
and ground flags on schematics.
I know, I know.
Ground should only be reserved for things that are connected
to earth ground but calling the common return path
in a circuit is now just accepted as ground.
So we'll just keep using that term for now.
Bring up the component chooser and search for G and D.
Select the G and D power flag symbol and click OK.
Place it below the 10 micro farad capacitor.
Hover over it and press C to copy it
to the other ground nodes as per the example diagram.
Open the component, choose it and search for VCC
which is a commonly used power flag for schematics.
Place a VCC flag next to the common pin on the switch
as this is what will allow us to connect and disconnect
battery power to the rest of the circuit.
Copy the flag to the other power flag locations.
Note that I like to leave at least one grid space
between components as it prevents confusion about
whether something is connected or not
when we go to add wiress.
Turned to wire select place wire,
click to start a wire from the left-most ground flag
and then click again to connect it
to the negative battery pin.
This tells KiCad that we intend for the negative battery
terminal to be connected to all the other ground node pins
such as to the negative pin on the two capacitors.
Click to start another wire from the battery's
positive terminal and connected to pin 3 of the switch.
Another way to add a wire is to use the W key.
Hover your mouse over the end of pin two of the switch
and press W.
A wire will automatically start from here.
If the wire isn't touching a second pin,
you can click to add a 90-degree bend which I'll do here
so that I can connect it to the VCC flag.
Continue connecting wires to our parts
as shown in the hand-drawn circuit diagram.
Note that some pins should be left unconnected.
Like pin 5 on the 7555 timer.
When you're done take a step back and look at your work
pat yourself on the back for finishing
the first major step toward making your board.
Don't forget to save your schematic by clicking file,
save schematic project and then close out of EE schema.
It always feels good to get the circuit drawn up
in schematic capture.
We're almost ready to move on to the board layout part
but first we need to see how to create custom foot prints
before associating those footprints
with our schematic symbols.
That will come on the next episode so stay tuned.
(fast paced music)