Logical switches are one of the most powerful features in FPV drone radios that run EdgeTX. It can be intimidating and confusing for newcomers. In this tutorial, I’ll explain what logical switches are in simple terms, how they work, and what you can actually use them for in FPV. If you are flying quads and just getting started with EdgeTX, this is one of those features you probably won’t touch right away. But once you understand it, you’ll realize how powerful it is.
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What is Logical Switch
A logical switch is a virtual switch inside your radio.
It is NOT a real physical switch you can flip with your fingers. Instead, the radio turns it ON or OFF automatically based on rules (conditions) you program.
Physical switches are practical, but also pretty “dumb” because they can only be controlled by the user. Logical switches let you create smart behavior in your radio. They are great when a normal switch is not enough.
For examples:
- “I want the radio to warn me when RSSI gets too low”
- “I want the radio to read out voltage when battery gets low”
- “I want the radio to reset timer 10 seconds after I disarm the quad”
So instead of physically flipping a switch, the radio is doing the switching for you based on logic, that’s why it’s called a logical switch.
And the possibility is endless, that is what makes logical switches so useful.
How to Differentiate Physical Switches and Logical Switches
- Physical switches are labeled with letters such as SA, SB, SC, SD, SE, SF, SG, SH, etc.
- Logical switches are labeled L01, L02, L03, L04… (up to L64 on most EdgeTX radios).
Where to Find Logical Switches in EdgeTX
To find and create logical switches:
- Press the MDL button
- Press PAGE a few times until you find Logical Switches
Basic Structure of a Logical Switch
Each logical switch has a few settings, but the most important ones are:
- Function
- V1
- V2
- optional AND switch
- Duration
- Delay
The basic idea is simple:
- Function = what test the radio should perform
- V1 = first value, the thing being monitored
- V2 = second value, the threshold or comparison value
For example:
- Function = a
- V1 = battery voltage
- V2 = 14.4V
That means:
Turn this logical switch on when battery voltage is less than 14.4V
Once that happens, the logical switch turns ON (active).
Delay
This means the condition has to stay true for at least this amount of time before the logical switch activates. That’s useful for avoiding false alarms. For example, if RSSI (or battery voltage) dips for a split second, I may not want an alert immediately. I can add a delay so the warning only triggers if the problem lasts long enough.
Duration
This controls how long the logical switch stays active. If I leave duration at zero, it stays on only while the condition is true. These features become more useful as your EdgeTX setup gets more advanced, for simple setup you can leave it unchanged.
Common Logical Switch Functions
- a = x → “1st value equals to 2nd value”
- a > x → “1st value is greater than 2nd value”
- a
- AND → Both conditions must be true
- OR → At least one condition must be true
- Edge → Detects when something just changed (useful for momentary actions)
- Sticky → Makes a switch “latch” (stay on until another condition turns it off)
There are many more functions available, check EdgeTX manual to learn more.
Note that you can also use logical switches and physical switches inside another logical switch (e.g. you can assign L1, L2, SA, SB etc to the V1 and V2 fields of another logical switch). It allows you to combine multiple conditions and create more advanced or complicated behaviors. It’s powerful but can get confusing fast and becomes very hard to debug later. Generally you want to keep your logic as flat and simple as possible at the beginning.
Example: Low Battery Warning
This is one of the easiest and most useful examples.
You can make a logical switch that says: Turn on when battery voltage is below 3.5V per cell.
- Navigate to Logical Switches on your radio
- Scroll to an empty line (for example, L01) and press ENTER
- Configure the logical switch as follows:
- Function: a
- V1: RxBt
- V2: 3.5V (you can change it to any voltage you want)
- Delay: 3 seconds (this delay reduces false positives caused by voltage sag during punchouts)
- Function: a
In the Betaflight CLI, enter:
set report_cell_voltage = onsave
Now L01 turns ON whenever your quad battery drops below 3.5V per cell.
Then in Special Functions, you can use L01 to play the value “RxBt” (with an interval of 10s so it doesn’t get too annoying). I also have another special function on the top that plays the voltage when I press the SH switch.
I have a whole tutorial that goes into detail how to set up low voltage alarm here: https://oscarliang.com/edgetx-voltage-callout/
What Can You Use Logical Switches For?
Apart from Low battery warning, beginner friendly uses of logical switches are:
- Low RSSI or low LQ warning: Use telemetry to warn you when your link quality drops.
- Automatic channel activation: Turn on a channel, LED, or feature when a condition is met.
- Safer Arming: if throttle is not fully low, radio alerts you it’s not safe when trying to arm
- Multi-purpose Knob: knob is already used in special function, but you can create a logical switch that checks knob position, then use that logical switch as the trigger for another special function
Any other creative use of logical switches? Let us know in the comments.
Final Thoughts
Logical switches sound more complicated than they really are. All they do is let me tell the radio:
“When this condition becomes true, treat it like a switch has been turned on.”
That condition might be any radio controls, telemetry data, or a combination of things
Once I have that logical switch, I can use it anywhere in EdgeTX just like a normal switch. You can even use logical switches and physical switches within another logical switch to create really complex behavior.
And once you get comfortable with them, you’ll start finding all kinds of clever ways to use them.
