Loraguide

loraguide

Hello! In this guide, you will create a custom Meshtastic-enabled LORA board with a microcontroller, antenna, radio chip, and other things.

First things first

To start your project, we need to download KiCad. KiCad is an open-source software for designing circuit boards, or PCBs. We can use the terms interchangably.

Go to https://www.kicad.org/download/ and install the version for your OS. After that finishes, create a new project. Name it anything you want, but I will name mine Loraguide.

After that finishes, you should be on a screen that looks like this:

The Schematic

The first step to designing a circuit board is the schematic. A schematic is essentially a wiring diagram, to show which components connect to what. That means it is very important that we follow a few design rules when creating our schematic:

• Power symbols always point up
• Ground symbols always point down
• Net labels can be used instead of wires

First, click Schematic Editor on the main project page. Hit the A key to open the symbol chooser. Search "esp32-s3" and select the ESP32-S3-WROOM-1.

Place it in the middle. Next, search for the SX1262 radio chip and place it to the left of the ESP32.

Power system

Organization

To keep things clean, use Power Symbols instead of drawing wires everywhere. Hit P, type +3V3, and place it on the 3V3 pin of the ESP32. Do the same for GND.

Power input

Search for "USB_C_Receptacle_USB2.0_14P".

Connect the GND pins to a GND power symbol. Note on the SHIELD pins: Do not connect these directly to GND. This can feed RF noise back into your host computer. For this project, leave the shield pins isolated or connected to a separate chassis pad if available.

Connect VBUS to a +5V power symbol. Place two 5.1k ohm resistors (R_Small) on the CC1 and CC2 pins and connect the other ends to GND. This ensures your USB-C charger provides the correct 5V.

SX1262 Power & RF

Power Decoupling

Chips draw sudden bursts of current. Decoupling capacitors (100nF and 10µF) act as local water tanks, sitting right next to the chip to handle these bursts.

Connect VDD_IN to +3V3 and place one 100nF and one 10µF capacitor between that line and GND.

The DCC_SW Inductor

The SX1262 has an internal DC-DC converter that requires a 15µH inductor on the DCC_SW pin. This inductor needs special care; it is a switching component right next to the radio. On the PCB, it must be placed as close as possible to the pin.

RF Output Matching

Simply running a wire to the antenna is inefficient and can be illegal because it emits harmonics. You need a matching network (filtering) on the RF output. This usually involves a series inductor and capacitors to GND between the RFO pin and the antenna connector.

5V to 3.3V conversion

Use an AMS1117-3.3 LDO regulator to convert the 5V from USB to the 3.3V our chips need.

USB Data, Buttons, and SPI

USB Data Lines

Connect the D+ and D- pins of the USB connector to the USB Data + and - pins on the ESP32. Use Net Labels (L) to keep the wires from crossing.

Boot and Reset Buttons

Both the EN (Reset) and GPIO0 (Boot) pins need a 10kΩ pull-up resistor to 3.3V. Connect push buttons that pull these pins to GND when pressed.

SPI & Control Wiring

PCB Section

Footprint Assignment

In Tools > Assign Footprints, assign the physical shapes. For resistors and capacitors, R_0402 or C_0402 are standard for these boards.

Placement

1. ESP32: Place at the top. Ensure the antenna "keep-out" area is outside the board edge.
2. SX1262 & U.FL Connector: Place these very close together.
3. DCC_SW Inductor: Place this right against the radio chip pin.
4. Decoupling Caps: Place them right next to their respective power pins.

Routing Order

Sensitive signals must be routed first so they have the cleanest, most direct paths.

1. RF Trace First: Shortest path from chip to antenna. Use 45-degree angles.
2. USB Data Lines: Route D+ and D- as a pair, keeping them similar in length.
3. SPI & Control Signals: Connect the communication lines.
4. Power Traces: 3.3V and 5V. Use wider traces (0.5mm) for these.
5. GND: Handled by the copper pour.

Ground Plane and Stitching

Add a Filled Zone (Z) for GND on both the top (F.Cu) and bottom (B.Cu) layers.

To prevent "floating" ground islands and interference, add stitching vias. These are small holes that connect the top and bottom ground planes. Place them around the perimeter of the board and near the RF trace.

Final Steps

Run the DRC (Design Rule Check) to find errors. Export your Gerbers and Drill Files, zip them up, and upload to a manufacturer like JLCPCB.

You have designed a grounded and RF-safe LoRa board.