Learn how to make a small keyboard with KiCAD

So you want to make a keyboard PCB? Don't know where to begin or how to proceed? You've arrived at the right place!

Getting Started

KiCad will be required. Download it, install it, and you're good to go!

... nearly.

We'll need some libraries as well. Hasu's keyboard parts component library and footprint library are my favorites, and /u/techieee has a good switch footprint library.

Download them all and we should be good to go!

Check that you have the official KiCad libraries as well. These should be included with your KiCad setup.

Schematics

Launch KiCad and start a new project (File > New Project > New Project). Whatever you want to call the project. For this guide, I'll refer to it as an "example." I know you're very inventive.

We'll begin by sketching out our schematics. When you double-click you.sch file, you should see an empty schematic sheet:

Let's start by adding our component library. Click Preferences > Component Libraries at the top of the window. Then, click "Add" and navigate to Hasu's library to locate the keyboard parts.lib file. Find the library you just added at the bottom of the component library list. We'd like to move it to the top of the list, so yours should look like this:

We're ready to go now that we've clicked "OK." Buckle up, because we're about to get really technical.

To begin, here is a list of basic commands:

m: pick the component up and move it
g: drag the component up and move it while keeping wires attached to it
c: copy the component
e: edit the component
r: rotate the component
y: mirror the component
del: delete the component
esc: abort!

Do Place > Component. Your cursor should now resemble a pencil. Place your cursor anywhere on the sheet. Look in the keyboard parts library for ATMEGA32U4:

Click OK, then click again on the schematic sheet to position the component. This is our commanding officer. Change the reference from "U?" to "U1" in the component. This is the one-of-a-kind name we'll use to refer to this specific component.

The crystal, which tells the controller how fast to run, is the next component we'll need to install. Locate and install the XTAL GND component next to the controller. Replace the reference with X1.

Next, we'll want to add two decoupling capacitors (C SMALL). These capacitors will essentially help prevent too much noise from accumulating in the signal to the controller. There is a formula for calculating the capacitance required for these capacitors, but for the time being, we'll use a crystal with an 18pF load capacitance, so these decoupling capacitors will be 22pF. Change their values to 22p and rename them C1 and C2. Add a GND symbol to represent ground as well, and connect everything with the wire tool (green line on the right) as follows:

Following that, we'll add decoupling capacitors for VCC, our power supply. We'll need one 0.1uF capacitor for each VCC/AVCC on the controller, as well as one 4.7uF capacitor for UVcc. In our case, we need four 0.1uF capacitors and one 4.7uF capacitor, as follows:

 

Let's connect a reset switch. You'll need a switch (SW PUSH) named SW1 and a 10k pullup resistor (R) named R1. If you're wondering why we need a pullup resistor and what it even means, Sparkfun has a good explanation. But for the time being, here's how it should be connected:

Put a 10k resistor called R2 on the HWB/PE2 pin and connect it to ground. A resistor is used here to tell the microcontroller that when we press the reset button, we want to enter the bootloader so that we can flash a new layout onto it!


Let us now add our USB port. J1. Add the USB mini micro B component from the keyboard parts library. VUSB should be connected to VCC and Uvcc, and two 22 ohm resistors R3 and R4 should be placed between the D- and D+ connections. Connect GND and SHIELD to each other and to ground. Finally, connect UCap and GND with a 1uF capacitor C8:

Let us connect all of the VCC and GND connections together. If you were using the built-in ADC (analog to digital converter), you would normally connect AVCC and VCC with a capacitor, but we don't care about that for a keyboard, so just connect them directly. At this point, everything looks like this:

Let us now construct our switch matrix. For this guide, we'll just make a simple 2x2 matrix. For our switch and diode components, we'll want to use the KEYSW and D components, respectively. Simply connect them as you would a hand-wired board, and remember to name them. K1 should be the same as D1, K2 should be the same as D2, and so on:

We need to connect this matrix to the controller now. Labels will be used for convenience (A with a green line underneath on the right). We'll use PF0 for row 0, PF1 for row 1, PF4 for col 0, and PF5 for col 1 in our example board:


Finally, mark all unused pins as not connected. Click on all the unconnected pins on the controller and the ID pin on the USB port with the no connect tool (blue X on the right). This is also a good time to double-check that you didn't miss any VCC or GND pins earlier! Our final design should look something like this:

 

Associating Components and Footprints

We must explain to KiCad what each of these components means. At the top, select the CvPcb icon:

If this is your first time using CvPcb, we'll need to import the footprint libraries that we downloaded earlier. Click Preferences > Footprint Libraries, and then use the "Append with Wizard" button in the window that appears to add the "keebs.pretty" and "keyboard parts.pretty" folders that we downloaded earlier. You may also need to add the built-in KiCad libraries manually. Your library list should now look something like this:

All of our capacitors and resistors will be assumed to be 0805 imperial sizes. Our ATmega32U4 will be housed in a TQFN package. For our diodes, we'll use Hasu's library's very useful hybrid through-hole and surface mount footprint. /u/1u techieee's switch footprint will be used for switches. The crystal will be of the FA-238 series. The reset button will be from the TL3442 series, and the USB mini B port will be from the Hirose 5S8 connector. Go through the list of footprints for each component and double-click on one to associate it with the currently selected component. Here's how all the associations should look in the end:

Save the assocations and close the window.

 

Generating Netlist

Now we'll create the netlist, which is essentially a list of the connections in our schematic. Select the netlist button:

Simply click "Generate" in the dialog that appears. In the save dialog, use the default netlist name. KiCad should not ask you about annotations if everything was properly laid out and named. If this is the case, click "Cancel," double-check all of your references, and then try again.

 

PCB

We can now start designing our PCB! Save your work and exit the schematic editor. Return to your project and open your ".kicad pcb" file. You should be greeted by a blank PCB editor:

The first thing we'll do is double-check that all of our footprints remain. Check that all of the footprint libraries you imported earlier are still present in Preferences > Footprint Libraries Manager. If not, just import them again.

Next, we'll create our grid. Set Units to Inches and Size X and Size Y to 0.09375, as shown: Dimensions > Grid

Then we want to instruct the PCB editor to use our custom grid. Change the top grid option to "User Grid."

Reading the netlist we generated earlier is the simplest way to get all of our footprints onto the board. Simply click on "Read Current Netlist" after clicking on the netlist button, which should look the same as before. A slew of messages should appear, and the dialog should look something like this:

Now press the "Close" button. You'll notice that there are now a slew of footprints stacked on top of each other in the center of the screen:


Let's hide the ratsnest, which is essentially the lines that detail the electrical connections on the board, before we separate them. Uncheck "Ratsnest" under the "Render" tab on the right:

Here are some useful commands for the PCB editor: