6.2 MCU Schematic - axolstudio-ca/Introductory-Guide GitHub Wiki
For the brain of the PCB, we will be using ATMEGA32u4. In my opinion, this MCU is the most beginner-friendly, with enough pins to do a full-size board and being extremely accessible and easy to work with. To add parts to the schematic use the hotkey a. In the search bar type in atmega32u4-AU and select ok.
Place the component anywhere on the schematic page. The schematic page should now look like this:
We will now start adding the power net to the MCU. As specified by the datasheet here (http://ww1.microchip.com/downloads/en/devicedoc/atmel-7766-8-bit-avr-atmega16u4-32u4_datasheet.pdf), we will tie UVCC, VCC and ACC to +5V. To add the +5V, use hotkey p and find the +5V symbol.
We will now wire it together. It should now look like this:
Next, we are going to wire the ground for the MCU. As specified by the datasheets, UGND and GND will need to be connected to the ground net. These pins are located at the bottom of the schematic. To do insert the ground net, we will use the hotkey p and find the GND symbol. Place and wire as follows:
We will now add the timing crystal for the MCU. Along with this crystal is 2 decoupling capacitors that we will need to add to it. The crystal will have its 2 data pins connected to XTAL 1 and XTAL 2. Search for Crystal_GND24_Small in the components and place it as follows:
We will now connect pin 1 to XTAL1, pin 3 to XTAL and rename the crystal to 16MHz using the e hotkey. It should now look like this:
Next we will add the decoupling capacitors. There are two 22pf capacitors and the component that we will use is C_Small. Wire the following:
We will next attach the VBUS line to the MCU, as the MCU will always need power. To do this simply add a +5V symbol and wire it to the VBUS pin.
We will next add a resistor to HWB/PE2 and connect that to ground. The component for the resistor that we are going to use is R_Small. Rename it to 10k.
We will now add resistors to the data lines. We will place two 22-ohm resistors as shown below:
We will now add the reset button. The component for a pushbutton is SW_Push. We will connect one side of the reset pin on the MCU and the other side to GND.
To prevent the reset button being accidentally triggered during normal use, we will add a pull-down resistor to the reset line. We will place a 10k ohm resistor between reset and +5V.
We will now add the other required capacitors for the schematic. Add a 1uF capacitor to UCAP and connect the other end of the capacitor to GND.
We also need to add the rest of the decoupling capacitors. We will need 3 0.1uF capacitors and 1 10uF capacitors connected to the power net. For all capacitors one end will be connected to +5V, and the other end to GND.
We will now add global lines for the datalines D- and D+. Click Ctrl+h to pull up the menu and type in the names D- and place it on the end of the corresponding pin from the MCU. Repeat for D+.
Your MCU Schematic should now look something like this:
