Low voltage alert

Mike Shellim 05 May 2018
updated 10 June 2019

One nice thing about OpenTx is that you can tailor your battery alerts according to their chemistry. So for example, for LiFe cells which have a flat discharge curve, it's best to use a timer as the primary alert, while for NiMH and LiPo cells monitoring the voltage is sufficient.

The snippet below shows how to trigger a voltage alarm using a single logical switch and a special function. It ignores short low voltage spikes.

L1: a<x, RxBatt, 7V, Delay(3s)

SF1: L1, Play Sound(Beep 1), repeat(4s)

For flight packs with sensors, use Cels as the first operand in L1.

Sound files

The example above uses a simple beep, but in practice I'd recommend playing a sound file. Most sound packs have lowbat and batlow voice; note however these provide only generic warnings, so I use my own "receiver battery low" sound file so there's no confusion about which battery is affected. Voice alerts can be difficult to hear in some environments, so consider also using the Haptic function. You can specify this in a second special function.