User Defines Explained¶
With more features being added consistently,
./src/user_defines.txt has gotten complicated 🤷♂️. So we will break it down! 🔨
*Note: This is the full list of currently supported User Defines and would help you should you intend to compile the firmware using the Toolchain or Manual Mode on the ExpressLRS Configurator.
- To enable/disable anything in the user defines, simply add or remove a
#in front of anything that has a
- We recommend reading this page in its entirety before first flashing ⚡ to have a better sense of the options.
-DMY_BINDING_PHRASE="default ExpressLRS binding phrase"
* This phrase gets md5 hashed and gets built into the binary you will be flashing.
#-DRegulatory_Domain_AU_915 #-DRegulatory_Domain_EU_868 #-DRegulatory_Domain_AU_433 #-DRegulatory_Domain_EU_433 #-DRegulatory_Domain_FCC_915 #-DRegulatory_Domain_ISM_2400
EU 868🇪🇺 is compliant to the frequency but is not LBT compliant 👂 . Every other band is near compliant 👿 but may not be fully compliant for your regulatory domain.
Note 1: Increase the telemetry rate with the ExpressLRS lua script. Increase the rate until the sensor lost warnings go away. It is normal to set it up to 1:16 with 200 Hz refresh rate.
Note 2: It must be enabled together with HYBRID_SWITCHES_8.
Default value is 320LU. If you want to change that you have to suffix your milliseconds value with LU. For example, in order to specify 100 ms telemetry update rate you have to enter it like this: 100LU.
Typically, you want to keep 320LU value for OpenTX based radios, and 100LU for ErskyTx ones.
HYBRID_SWITCHES_8changes this to 1x 2-pos + 6x 7-pos + 1x 16-pos, with only the 2-position being low-latency. In Normal Mode, all switches are sent with every packet, in Hybrid Mode, only AUX1 is sent with every packet and the rest are rotated through. Note: The switch mode MUST match between the RX and TX. A detailed explanation of the differences between the two options can be found in Switch Modes, but 1. If only two position switches are needed, and they must be updated as fast as possible: Normal Mode 2. Almost everyone: Hybrid Mode (Put ARM on AUX1)
Output Power Limit¶
There has been some reports of the R9M modules showing instability at >250mw with stock cooling. This in part because the ELRS uses a higher duty cycle for transmission compared to stock firmware. By default the power of any TX is limited to 250mw but you can unlock up to 1000mw (for hardware that supports it) by enabling the following option. Do this at your own risk if you make no cooling modifications-- R9M modules will burn themselves out without cooling.
AUX1 is the channel ExpressLRS uses to detect "ARMED", and this feature assumes that a low value of the arm switch is disarmed, and a high value is armed. OpenTX can invert your switch if you prefer it to be mechanically inverted. It may be best not to enable no sync on arm when you are first setting up ExpressLRS as it can be a source of confusion.
0, but is experimental (even in 1.0) and is best left disabled.
Both require OpenTX
2.3.12 or above. In order to install it, you will have to use OpenTX companion application.
Deviation radio users such as those with the T8SGv2/v3 should disable this feature.
You can also use EdgeTX.
LOCK_ON_FIRST_CONNECTIONis used, ELRS will not cycle after a disconnect, but instead just stay on whatever rate the last connection was. This makes connection re-establishment quick, because the RX is always listening at the proper rate. This is generally what everyone wants, but there is utility in being able to switch the TX to the lowest rate to get more range to re-establish a link with a downed model, which can't happen if the RX is locked at the previous rate.
When cycling through the rates, the RX starts with the fastest packet rate and works down to the slowest, then repeats. It waits
PACKET_INTERVAL * PACKS_PER_HOP * HOP_COUNT * 1.1 at each rate. Example: 4ms * 4 * 80 * 1.1 = 1.408s for 250Hz. The duration is extended 10x if a valid packet is received during that time. Even with
LOCK_ON_FIRST_CONNECTION, the rate can be changed by changing the TX rate using ELRS.lua while connected, or by power cycling the RX.
ESP32based TXes (will not work with modules without built-in inversion/uninversion), but enables compatibility with radios that output inverted CRSF, such as the FrSky QX7, TBS Tango 2, RadioMaster TX16S. You want to keep this enabled in most of the cases. If your radio is T8SG V2 or you use Deviation firmware turn this setting off.
F4 FCswhich only have an inverted receiver input UART RX. 🔼. This is only one way, so you lose the telemetry downlink to your radio as well as passthrough flashing. Enabling this turns on CRSF protocol output on the
S.BUS🚌 pin on your
set serialrx_inverted = ONmay also be needed within Betaflight 🐝 for compatibility
ESP8285on it if no TX connection is established after N seconds from boot (the 30 is the time). This enables pushing firmware updates to the RX by connecting to its wifi network and visiting
#-DJUST_BEEP_ONCE #-DMY_STARTUP_MELODY="<music string>|<bpm>|<semitone offset>" -or- #-DMY_STARTUP_MELODY="<rtttl string>"
For all your customization needs, use
DMY_STARTUP_MELODY to define your own startup melody using the BlHeli32 or RTTTL syntax. For BLHeli32, the parameters
music string and
bpm are required, whereas
semitone offset is optional to transpose the entire melody up or down by the defined amount of semitones.
Example BlHeli32 melodies are available on Rox Wolfs youtube channel, some experimentation may be required though. To write your own melody, this (Sheet Music 101) and this (BLHeli Piano) are useful resources.
The build process also supports RTTTL-formatted ringtone strings. RTTTL melodies are delimited by colons
: and start with a description versus the BLHeli style with have pipes
env:FrSky_TX_R9M_via_WiFi) 🖥️ and debugging via WebSocket 🔍. Uncommented by default, does not need to be changed.