The E77 Easy Solder Boards are designed to allow one with minimal soldering skills to build their own mLRS hardware. All of the parts except for the E77 module are through-hole parts to aid in assembly. These boards are flexible in that they can be used as a Tx module, receiver or SiK replacement. Additionally, these boards support diversity when paired with an additional E22 module.
| Frequency Bands | 868 MHz/915 MHz (E77-900M22S) or 433 MHz/70 cm (E77-400M22S) |
| Max. RF Output Power | 22 dBm (158 mW) |
| Supported Modes | 31 Hz, 19 Hz |
| LoRa Chipset | SX126x |
| Compatibility | Compatible with MatekSys mR900, SeeedStudio Wio-E5, EBYTE E77 MBL. Incompatible with SX127x hardware (Frsky R9 and ELRS 900 MHz). |
Note: EByte silently changed the hardware of the E77 module around the beginning of 2024. These newer modules use a (better) TCXO, whereas the older modules use a ceramic crystal oscillator. According to the datasheet, newer modules can be identified by serial number SN ≥ 3202995. The new and old modules require different firmware. The old modules will need firmware with the label "-xtal" in the name. Also, some reports suggest that one needs to use NRST (reset) for flashing via SWD.
Connections (name in respect to board print-ons, otherwise please refer to graphic):
| serial: | Tx, Rx |
| com / cli: | Tx, Rx |
| JRPin5 / in: | S |
| bind: | button |
| debug: | STx |
Note: To enable the cli, hold down the bind button during boot.
Connections (name in respect to board print-ons, otherwise please refer to graphic):
| serial: | Tx, Rx |
| out: | S |
| bind: | button |
| debug: | STx |
Note: In order to send RC channels over the serial connection (no need for OUT wire), change the "Rx Snd RcChannel" parameter to 'rc override' (or 'rc channels' if possible).
Important: Every time that you power a board you should ensure that there is an antenna connected otherwise you risk damaging the RF section.
- Download and install STM32CubeProgrammer
- Connect your ST-Link to the 3V3, GND, SWD, and SWCLK pins on the board (image below)
- Refer to the diagrams above
- Some ST-Link boards provide power and some do not - ensure the board is powered
- It might be necessary to also connect the reset pin on the board to the ST-Link's NRST
- Launch STM32CubeProgrammer and select ST-Link as the connection method, click connect
- From the menu on the left select the Download tile
- Select the correct firmware in the Download section, click Start Program
- Power cycle the board, the red LED should blink which indicates that the board is disconnected
Note: If you are unable to flash due to readout protection, perform the following steps after connecting to the device:
- From the menu on the left select the OB (Option Bytes) tile
- From the Read Out Protection section, change to AA, select Apply
- This will erase the current firmware
As mentioned in the introduction, with the exception of the E77 and E22 modules the board uses only through-hole parts, which makes soldering as simple as possible. Moreover, standard parts are mostly used, which should help with sourcing. Only the two 1.8 mm LEDs are somewhat special and less common, but can be substituted with standard 3 mm LEDs if necessary.
The electronic scheme and board design files, as well as Gerber files for ordering PCBs, can be found here.
| R1,R2 | 330, 1/4 W |
| C1,C2,C3,C5* | 10u, RM3 |
| C4,C6* | 100n, RM2 |
| IC1 | LD1117AV33, TO220, low drop fixed voltage regulator 3.3 V, 1 A |
| IC2 | Ebyte E77-900M22S |
| IC3* | Ebyte E22-900M22S |
| LED1 | red LED 1.8 mm |
| LED2 | green LED 1.8 mm |
| SW1 | button 6 x 3.5 mm |
* The parts C5, C6 and IC3 are only required, and only need to be populated, when diversity is desired.
For convenience, a Mouser list is available here. The Ebyte modules can be purchased on Aliexpress.