ELRS2.4G receiver

Updated
2022-09-11 Updated antenna related content
2022-09-18 Added version 3.0.0 firmware
2023-05-30 Added version 3.2.1 firmware 
0.
The receiver of the ELRS2.4 ceramic antenna in the hand has more interference in the community The performance is poor. The price of 60-100 with PA+LNA on Taobao makes me feel that it is not worth it. Since the firmware is open source, the circuit of the receiver itself is relatively simple. In the spirit of open source, I am going to make one myself. ELRS2.4 receiver with PA+LNA
1. Hardware design
The matching circuit output by SX1280 directly uses the official reference circuit, and the component parameters of the circuit also directly use the official recommended numerical values.
The RF part of the circuit is mainly composed of three parts, matching circuit, bandpass filtering and DC blocking capacitors. In fact, the main thing that affects the RF performance behind the board is the matching part. This part requires professional equipment for optimization. I don’t have professional equipment here. I use the recommended parameters for design and control the wiring. Just impedance.
PA+LNA uses AT2401C. You can design the circuit by referring to the manual.
2.
The RF circuit requires impedance control. When making the board, be sure to select the impedance control board. The thickness of the board is 1mm + JLC04161H-3313. The lamination sequence of the stacked structure
is GTL-G1- G2-GBL
! ! ! !
The board is designed with AD. It is recommended to use Gerber files to place orders. The original drawings and PCB imported by Lichuang EDA are for reference only
. 3. Soldering:
Soldering this module requires at least hot air Q and solder paste. It is recommended to solder with Teppanyaki on one side for SX1280 and for ESP8285 on the other. The cost of selling SX1280 directly with hot air Q welding
is relatively high. I dismantle and use it from the finished module. I recommend the SX1280 module of Silicon Heirloom. Basically all the resistors and capacitors on the module can be reused. The
matching circuit part is because the parameters of the components are small. , cannot be directly measured. I used the RF matching circuit removed from the module and the RF matching circuit with the marked value in the circuit diagram to compare and test on the same board. The RF matching circuit with the marked value will have about 3dbm higher signal strength than the removed module at the same signal strength. It is enough to remove the module. If you need better performance, you can use the marked value.
4. Firmware programming
requires a USB to serial port module for initial use. Subsequent updates can be made via wifi, using the BFPV Nano 2G4RX firmware, which is attached in the attachment
. 5. Cost
SX1280 module 13
ESP8285 5.5
crystal oscillator 2
passive components and interfaces 6
Total 26.5
6. The finished
transmitter uses self-made ELRS2.4. The signal strength is about 500m
when taking off with 100mW power
. At this time, the sky is facing you, and the intensity will reach -70dbm when turning.
You can also fly with your own antenna, and the cost is extremely low, less than 1 Yuan, the effect is consistent with the commercially available copper tube antenna (actual measurement), and may be slightly worse than the commercially available T-type antenna with Balun (not tested).
Choose a 113-wire IPEX single-ended wire with a length of 15CM to
select the feed point position . , cut the RF line at the +3CM position of the feed point, and cut the part without the IPEX head into a 3CM line segment. Clamp
it with needle-nose pliers. You can directly pull out the Teflon core inside and
control the position of the feed point. Use a knife to cut the black Pull out the plastic layer and metal shielding net with force; then gently scratch the black plastic layer, leaving 1-2mm of shielding layer. Weld the antenna.
Weld the previously removed wire core to the shielding layer
. Adjust the antenna to the level and control The length of the upper part of the T is within the range of 54.6-54.8mm. This length must be strictly controlled as it will affect the performance of the antenna. The wavelength of electromagnetic waves of the same frequency will change in wire diameters of different diameters, and will change to the original in 113 wires. is about 0.89, so the 54.6-54.8mm range mentioned above is only applicable to the 113 line.
After completing the length control, it can be used directly by adding some hot melt glue to the feed point for reinforcement. If you have the equipment, you can print a T-shaped protective case. Results of
final product
VNA analysis