μLRS - micro LRS receiver, OpenLRSng compatible
RCGroups thread: http://www.rcgroups.com/forums/showthread.php?t=2371835
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
μLRS boards are hardware compatible with OpenLRSng firmware for HW 8 (micro RX). Common features for μLRS boards are:
- input voltage 4-16V (max 3S lipo, 4S is too much voltage)
- PCB pads for 3.3v UART interface (RX, TX, DTR, GND) - do NOT try to use it with 5v uart interface
- analog RSSI output pad
- U.FL antenna connector
- RFM22b 100mW radio module
- LFCN-490 low pass filter (can be easily removed by replacing it with 1206 0R resistor)
- LC filter for radio power supply
- Atmega328P-MU microcontroller (QFN case)
- 0603 sized components - can be soldered at home (only atmega chip requires strong soldering skills)
Improved version of μLRS v1 with following changes:
- vias covered by soldermask (v1 has these with copper epxosed)
- removed I2C pads
- removed 3.3v pad
- removed resistors in TX/RX pads
- removed dedicated RESET pad (but still easily accessible at the most bottom-right capacitor pad)
- smaller board - 16x16mm (0.63" x 0.63"), exactly the same size as RFM22b module
- PCBs can be ordered here: https://oshpark.com/shared_projects/H6KfYEk2
- 4x 1k 0603 resistor
- 1x 10k 0603 resistor
- 2x 22p 0603 capacitor
- 4x 100nF 0603 capacitor
- 2x 1uF 0603 capacitor (on schema one is 0402, but 0603 fits perfectly and is easier to solder)
- 2x 10uF/6.3v 0603 tantalum capacitor
- 1x 47uF/16v SMD B tantalum capacitor (schema is for SMD A, but 16v SMD A cannot be found, you can use SMD-A 6.3v but then you are limited to 5v power supply)
- 1x SOT-323 Schottky diode (let it be around 200mA), for example BAT165
- 1x green 0603 led
- 1x red 0603 led
- 1x LFCN-490 filter
- 1x mcp1703cb SOT23 voltage regulator (supports max 16V)
- 1x 16MHz crystal oscillator 3525 case
- 1x 10uH 1210 inductor
- 1x Atmega328P-MU (MLF32 case) microcontroller
- 1x RFM22B-433-S2 radio module
- 1x U.FL antenna connector
μLRS v1 is a first prototype board:
- PCB dimensions: 20x18mm
- I2C interface (SDA, SCL) pads
- 3.3v pad
- RESET pad (for SPI programming)
- big 47uF tantalum capacitor for input voltage filtering
- two 10uF tantalum capacitors (one for 3.3v filtering, another one for RSSI analog output)
- can be used also as a transmitter
- PCBs can be ordered here: https://oshpark.com/shared_projects/nFa7UehY
