The main purpose of using a PWM receiver is to drive servos and ESCs directly with PWM signals without an FC. But did you know that ExpressLRS PWM receivers can also output serial protocols like SBUS and CRSF, just like a standard serial receiver? In this tutorial, I’ll show you how to enable it. This makes PWM receivers far more versatile across different models, opening up many new possibilities.
New to ExpressLRS? Start here with our ELRS basics tutorial: https://oscarliang.com/setup-expresslrs-2-4ghz/
What’s Required?
Nothing—just your ExpressLRS PWM receiver!
In the past, if you wanted digital signal like SBUS or CRSF from a PWM receiver, you’d need an external serial converter. But with ExpressLRS, no additional hardware is necessary. These ELRS receivers are so powerful they can generate serial protocols directly.
When to Use SBUS or CRSF
PWM outputs are ideal if you’re not using a flight controller (FC)—for example, in many fixed-wing models where servos and ESCs connect straight to the receiver (for example I did that in my Heewing T1: https://oscarliang.com/hee-wing-t1-ranger-no-fc/).
But when using a flight controller, serial protocols like SBUS or CRSF are better:
- SBUS uses just one wire and supports up to 8 channels.
- CRSF is bi-directional, requiring two wires, supports more channels as well as telemetry.
For PWM Receivers Without Dedicated Serial Output
Some ExpressLRS receivers—don’t have a dedicated serial port. In these cases, you can re-purpose PWM channels to act as serial outputs. These receivers include: the Radiomaster ER3Ci, ER4, ER5A, ER5C, ER5Ci, ER5V2, ER6G and ER6GV.
Here’s how:
Power on the receiver.
Enable WiFi mode (either via the ExpressLRS LUA script on your radio or by waiting 60 seconds).
Connect your laptop/phone to the receiver’s WiFi network (ExpressLRS RX) and open the Web UI by entering 10.0.0.1 in your browser.
Under PWM Output, set Channel 2 to “Serial TX”. CH3 will automatically be assigned as Serial RX by default. This means PWM outputs 2 and 3 become your serial port.
Under Serial Protocol, select CRSF or SBUS (regular or inverted). You’ll also see other options like MAVLink, HoTT Telemetry, DJI RS Pro, and SUMD, making this feature extremely flexible.
Click Save, and you’re done.
Here I configure my receiver to output SBUS and confirm it’s working using my SBUS tester. In case you’re curious, the tool I’m using is the ToolKitRC MC8 Battery Checker. It can double as a signal generator and reader for PWM, PPM, and SBUS—very useful for troubleshooting and testing RC-related gear: https://oscarliang.com/toolkitrc-mc8/
Note: The remaining PWM channels will still work as normal. For example, if CH2 and CH3 are reconfigured for serial output, CH1 will still output throttle, and CH4 will still output yaw (assuming your channel map is set to TAER).
For PWM Receivers with Dedicated Serial Output
Some ExpressLRS PWM receivers include a dedicated serial output port (with RX and TX pins labelled), such as the ER6, ER8, ER8G, and ER8GV.
With these receivers, you don’t have to repurpose PWM channels for serial output. However, if you want, you can still configure two PWM outputs to act as a serial port—the flexibility is there.
Power on the receiver.
Enable WiFi mode (via the ExpressLRS LUA script on your radio or by waiting 60 seconds).
Connect to the receiver’s WiFi network (ExpressLRS RX) and open the Web UI at 10.0.0.1.
Under Serial Protocol, select CRSF or SBUS (regular or inverted).
Click Save. That’s it!
For Non-PWM Receivers (Serial Receivers) to Output SBUS
By default, all ExpressLRS serial receivers output CRSF. If you want SBUS output instead, follow this full tutorial: https://oscarliang.com/how-to-output-sbus-from-an-expresslrs-receiver/
The great thing is you can configure whether the receiver outputs inverted or uninverted SBUS:
On F4 flight controllers:
- If your board has a dedicated SBUS pad, it’s likely to have an built-in external inverter, in this case, select inverted SBUS.
- If it doesn’t have a SBUS pad, and you are only using a standard UART (RX pad), select uninverted SBUS.
On F7 flight controllers, it doesn’t matter—they support both natively.
Conclusion
Enabling SBUS or CRSF on ExpressLRS PWM receivers makes them far more versatile, letting you adapt to different setups without needing to buy a separate serial receiver. Thanks to the powerful and flexible ExpressLRS hardware, the process is simple and straightforward, yet unlocks huge potential.
