Setup Reliable Low Voltage Alarm on Taranis using Logical Switch

If you use Telemetry and voltage warning on your Taranis TX, you might notice the frequent false alarms due to voltage fluctuation, e.g. sudden drop in voltage due to punch-outs. In this tutorial we will show you how to set up Logical switches to make a more reliable voltage alarm.

For beginners, we recommend you to take a look at this guide on how to setup a simple voltage alarm to gain a basic understanding how this work.

Also check out this list for more awesome Taranis hacks and tricks.

Disclaimer: There are million ways to achieve the same thing, this might or might not be the best or most efficient way, but it works great for me. Please let me know in the comment if you have different ideas.

Why set up voltage alarm on the Taranis?

There are many ways to monitor your battery voltage, such as using OSD and voltage alarm buzzer. But my favourite way is to use the Taranis for low voltage warning.

You can make a low voltage alarm easily in the Taranis using simple logical switches, but the amount of false alarms can be both annoying and confusing.

So in this article I will show you how I setup a more reliable and sophisticated low voltage alarm.


Step 1 – Setting up Logical Switches

Logical switches are just virtual switches, they can be activated when certain conditions are met.

We can use these switches to create audio and visual feedback both on the Taranis and on your quad. For example, to play a warning, or read out the battery voltage :)

On your Taranis, go to the page “Logical Switches” by pressing the [MENU] button once, and press the [PAGE] button to skip to the next page.

The following screenshot shows the logical switches on my Taranis.

They might look a bit daunting, but they are actually quite simple! i will explain the purpose of each of these Logical Switches.

Logical Switch Conditions Info
L01 a<x   VFAS   14V   L02 This is our primary logical function, it will activate when VFAS (our battery voltage) gets below 14V and when L02 is on (you can set it to any voltage you want, 14V is a good value for 4S LiPo batteries)
L02 a>x   VFAS   0   L03 This switch is used to avoid false alarms when we are just powering on the Taranis TX. When Smart Port is initiating, VFAS will read 0V. This switch is only on when L03 is on.
L03 a>x RSSI 0dB This switch is also used to avoid false alarms, when Telemetry connection is lost.
L04 Edge   L01   [4.0:<<] Battery voltage on our mini quad can jump up and down a lot, and the edge switch is there to prevent false alarms caused by voltage fluctuation.
It will only activate when L01 has been activated more than 4 seconds, i.e. it will only turn on when voltage is below 14V for 4 seconds or longer. The switch will not activate when L01 suddenly deactivates before the 4-second is reached, i.e. voltage is recovered above 14V.
L05 a>x   VFAS   14V This switch is used by the next switch, it simply checks if the battery voltage is recovered above our threshold voltage
L06 Stcky   L04   L05   L07 This is the switch we will use in our Special Function.
The Sticky switch activates when the first parameter is activated (L04) and it turns off when the second parameter is on (L05). This switch stays on or off until the one of the parameters changes state, thus the name “sticky switch”.
L07 Timer   6.0   0,1 Without this timer switch, the voltage warning will only trigger once, if that’s what you want you can simply remove this switch. Using this timer switch, the warning can every 6 seconds (you can change to whatever duration you prefer). Beware this switch is added to the “AND” function of L06.

To summarize what we have so far… L06 is only activated when the voltage drops below 14V for more than 4 seconds (L04), and L06 is disabled when the voltage rises above 14V (voltage sag recovers or new LiPo attached). The timer switch will ensure the warning is triggered every 6 seconds.

Step 2 – Setting up the warning

There are more than 1 way to inform yourself of low voltage, you can choose to:

  • Play an audio track, that says “Warning, voltage is getting low, please land ASAP” or something like that :)
  • Or simply read out the voltage

I personally prefer to just know the actual battery voltage, so in the next page, “Special Functions”, assign L06 to a function, and select “Play Value” and “VFAS”.

That’s all! Now the Taranis will keep telling you your battery voltage every 6 seconds when it’s below 14V, most importantly you should get the minimum amount of false alarm.

If you have any questions, feedback or improvements to this script feel free to share them in the comments.

Edit History

  • Jun 2016 – Article was first created by guest writer, Salih Ergezen
  • Nov 2017 – Updated Logical switches for the latest OpenTX 2.2 and some improvements were made

25 thoughts on “Setup Reliable Low Voltage Alarm on Taranis using Logical Switch

  1. Ed Scott

    Instead of L1 checking L02 (Above 0) and L03 (RSSI) why not just check that the ARM Switch is High, mine is SG. This will also prevent avoid false alarms when we are just powering and saves 2 steps.

      1. Chris lowe

        I like the way this works over any of the throttle position based setups. However I am having an issue I haven’t found the solution to yet. Once the alarm trips and i land. If the voltage did not climb above 14v before I unplugged the quad. The sticky is still updating and warning every 6 seconds. I either have to turn my transmitter off, or plug in a new battery to stop it. How can I get it to recognize that it’s unplugged and disable the sticky? Can I trigger it based off arm status, or have it look for rssi below a threshold?

      2. Oscar Post author

        okay, maybe we can add another logic in there with throttle level, or arm status like you said (switch position), but I think throttle level is better. When you’ve landed, throttle level should be lower than 5% or something… i will revisit this when i have time.

  2. Beeb

    For OpenTX 2.2, the Edge switch must have the following time constraint: [3.5:<<]. Otherwise, the switch will wait until L1 is false to trigger.

  3. Frank

    Please ignore the former post.
    Confirmed working on OpenTx 2.2 and with a certain elegancy:
    L01 as above
    L02 as above
    L03 a>x RSSI 5 dB —- 0,0 0,0
    L04 SRFF L01 L02 L03 0,0 3,5

    Best regards, Frank

  4. cahe

    This doesn’t work anymore. Please update according to changes to Edge switch in recent opentx releases.

    1. Oscar Post author

      Yes the old version was outdated, we have just updated the script for OpenTX 2.2.
      Everything should be working now.

  5. Rigo Torres

    Hi Oscar,

    Thanks for the writeup, very useful. I’m new to the Taranis, got it last night. Everything is set up but I did find the voltage warnings annoying on punchouts.

    Quick question though, what if we wanted to add two warnings one for battery low and one for battery critical? Would it be a matter of copying the first 4 switches again with different values?

    I think I’m missing a step somewhere so that it stops giving me low battery and to just give me battery critical after it drops under a certain threshold.

    Thanks Oscar :)

  6. Edgar

    I added one more switch that there is no alarm if the voltage is below 1V. I did this to avoid the annoying warnings if my main battery is not connected i.e. if I configure CleanFlight.

  7. Aaron

    Wow gonna try this. Im wondering why my Taranis warns me at the right time battery is critical . Battery voltage is reading back correctly on the screen . But she says 3volts all the time 3v , 3v, 3v. no matter what the voltage is.

    1. Mark

      Sounds like you have updated your firmware on your taranis. Believe it or not you need to download a new sound pack. I had this problem, i also have a custom sound pack, I solved it by getting the new pack and looking at the differences and found the sound files for decimal numbers and added those to the radio, works as advertised now.

      1. TomDrone


        It doesn’t really work in my case. I have all new sound pack (including sounds for decimal numbers) but it doesn’t work as you write. I’m facing the same problem as Aaron when amber is saying 3 volts all the time.

        Whichever forum or facegruup I ask the question about it I got the same answer – update sound pack to newest one which is not really a solution.

        Oscar – this might be something for you ;-)

  8. Adriano

    Liked your solutuon! And learned some new functions, thanks!
    Just sharing how Its mine…
    I use only one function (like yours L1), addind the seconds on duration and delay columns (last 2 columns)…
    This function triggers a playtrack like you do.
    I don’t use feedback to the quad, as the tx is always near (and “singing”). I also have a channel/switch to activate beep on flight control (used only as a beacon when crash).

    1. Mark

      Yeah i’m not sure if i’m missing a benefit to using “edge” over the delay feature in every single logical switch!

  9. David Kyjovský

    I use a similar system – except instead of using a delay, I suppress the alarm IF my throttle is above certain threshold (like 20% above mid throttle). Works great.

  10. Sketch

    I used the throttle stick to avoid false battery warnings on punch outs, a lot less complicated. Instructions in this video.


  11. Paullex

    Hi Oscar, your Battery source is A4? If I am using X4r-sb, using smartport, should I be using Vfas as source and instead of individual cells (3.6 etc) I use the full pack voltage (ex. 14.6)?


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