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Introduction
The 12V -> 5V @ 4A Buck Converter + ELRS Board is intent for several foam fixed wing planes at the Waterloo Aerial Robotics Group. It includes a ESP32-C3 for PWM signalling signaling and SX1281 for RF control over ELRS, as well as the requisite power electronics to have the system be powered by a single 12V input (1x 3S battery).
Please read the usage section for important details!
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This implementation is designed to optimize and integrate the system of the foam fixed-wings, which currently requires a separate buck converter (previously using 12V->5V @ 5A Buck Converter Board), and a commercial, off-the-shelf ELRS receiver (https://betafpv.com/products/elrs-micro-receiver).
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Espressif ESP32-C3 (FH4 model with 4MB flash)
1x chip antenna for ESP-32C3
Can be used for WiFi flashing.
6x PWM header pins for servo control (2.54mm pitch)
2 are placed to be connected to ESCs
1x input XT60-M connector
designed for 3S battery (12V input)
2x output XT60-F connector
12V output for up to 2 ESCs
SX1281 RF IC
1x U.FL connector for external RF antennaConnected to the RF IC.
Impacts RC performance
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Usage
This board is designed to use a single 3S battery for input power. This will split the power into two output XT60 connectors, and feed to the buck converter, which, in combination with an LDO, powers the rest of the device.
The power rail is rated for an absolute maximum of 16.9V, accounting for LiPo battery overcharging and input transients (voltage spikes from hot-plugging a high-inductance battery). Usage of a battery with an anti-spark connector is recommended.
Do NOT leave the U.FL connector unoccupied when powering on the device. Without a load to match the output impedance, any power transmitted will reflect back as a standing wave and likely destroy the amplifier in the SX1281 RF IC.
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This board was built to follow the Generic C3 2400 PWM target in the ExpressLRS examples on GitHub. The pin definition is as shown.
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Flashing
The board should be able to flash over UART. Use the GPIO9/PWM1 pin header and pull it low during chip reset (on-board button labelled ESP_RST). This will put the ESP32C3 in Joint Download Mode.
Use PWM5/6 as UART receive/transmit, respectively. Alternatively, the GPIO18/PWM3 and GPIO19/PWM4 pins can be used for USB-Serial-JTAG Download Boot.
Schematic
Altium 365 | 12V-5V 4A Buck with ELRS
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https://github.com/ExpressLRS/targets/blob/master/RX/Generic%20C3%202400%20PWM.json
View file name 12-5V Buck Converter + ELRS RX.step