CRSF/ELRS on the esp32 chip

[mishgant187-cloud]

Hi. This is a very interesting project. Have you tried using the ESP as a flight controller and CRSF protocol receiver on the 2.4 GHz chip itself?

[rtlopez]

Do you mean communicate to SX chip directly from FC? External ELRS receriver works on uart like a charm. I'm using it on my test rig.

[mishgant187-cloud]

The ESP itself can be a receiver. Have you tested combining the flight controller and receiver on the same ESP chip? (the 2.4 frequency allows for this)

[bsvdoom]

You can’t make the ESP32 chip itself act as a CRSF radio-link receiver because CRSF (Crossfire/ELRS family) expects an RF physical layer and modulation the ESP32’s built-in Wi-Fi/Bluetooth radio can’t reproduce or tune to.

TBS Crossfire and many long-range RC systems use sub-GHz (e.g. 868/915 MHz) or dedicated LoRa/FSK modems (Semtech SX127x family) for the air link. The ESP32’s on-chip radio is a 2.4 GHz Wi-Fi/BLE transceiver — it isn’t tunable to sub-GHz bands and isn’t intended to act as an arbitrary FSK/LoRa modem.

CRSF/ELRS/Crossfire use specific physical-layer modulations (LoRa or proprietary FSK modes) and timing/packet formats that require a radio modem (SX127x or a dedicated transceiver) or very low-level radio access you don’t get from the ESP32’s Wi-Fi/BLE stacks. You can’t just “switch the ESP32 radio to raw LoRa/FSK” in a supported way.

See #138

[mishgant187-cloud]

The instructions say: "To use Serial RX on ESP8266, you need to connect the receiver to the primary UART." Can you please explain why this works?

[bsvdoom]

The instructions say: "To use Serial RX on ESP8266, you need to connect the receiver to the primary UART." Can you please explain why this works?

In short: only UART0 has an RX pin.

Because CRSF (and any serial protocol) needs a bi-directional serial link — especially for Crossfire/ELRS telemetry.
The ESP8266’s secondary UART (UART1) physically cannot receive, so you must connect the receiver’s TX line to a pin that actually connects to an RX input on the ESP — and that’s only on UART0.

That’s why the documentation or examples say:

“To use Serial RX on ESP8266, you need to connect the receiver to the primary UART.”

They mean:

Use UART0, because it’s the only UART that can receive data.

The “primary UART” = UART0 (GPIO1 TX / GPIO3 RX).

[mishgant187-cloud]

Can the esp8285 be connected to UART0 or can it be connected to UART1-2?

[bsvdoom]

On esp8266 only UART0.

[mishgant187-cloud]

Still can't solve the problem: I have configured the receiver and the remote (connect to each other), but the CRSF commands do not go to the esp32-S3. Please tell me what could be the problem and where I should look? As a receiver: BETAFPV 2.4GHz Lite RX
Firmware Rev. 3.5.6 (ee188b) ISM2G4

Photo.zip

[mishgant187-cloud]

UART pins 13 and 14

[rtlopez]

1. wrong pins, probably you want to use 15 and 16 https://github.com/rtlopez/esp-fc/blob/master/docs/wiring.md#default-uartserial-pin-mapping
2. also remember to cross RX-TX
3. in ports tab tick serial rx function on port you want to use
4. in receiver tab choose serial and CSRF

[mishgant187-cloud]

Can't we reassign UART ports?

[rtlopez]

Yes, you can, but you need to unmap pins if they are assigned to diferrent function, in you case 13 is assigned to SPI

[mishgant187-cloud]

Are the port assignments removed by setting roles to other ports? SPI is 35-37 for me, and they work (gyroscope and accelerometer data). Are the assignments removed through the console?

Photo.zip

[rtlopez]

I see that pin 14 is assigned to input_rx and serial_2_tx. Also you shuldn't use pin 15 as adc, because it is assigned to hardware ADC2 which is utilized by wireless components.