Pixhawk Details #4: Audio adds Safety

This video illustrates a bit better why we believe the safety switch, buzzer and multicolor led help to greatly improve ground and air safety. The video just showcases a few new key safety features and is not a complete reference / mapping, as blink patterns might differ depending on the flight stack running and/or user settings.  Some details:

  • The safety pushbutton indicates safety on with a slow blink pulse and becomes solid when armed
  • The main led shows the breathe pattern if disarmed and becomes solid when armed
  • Arming is only possible after the safety has been disengaged. This is to prevent accidental arming via RC
  • On arming, the buzzer first emits the arming tune, and then the props are slowly spun up to (a configurable) idle speed after a short delay. User tests show that users can disarm fast enough if having accidentally armed.
  • There are two distinct low battery patterns for low and critically low battery. Since the buzzer is driven with 32V, it can be easily heard from a distance, so even when not looking at the GCS and battery voltage, there is now an intuitive warning, in time to land safely.

We believe that this will greatly help to improve situational awareness of the pilot and prevent a range of potential ground and air accidents.

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Comment by Gary McCray on September 16, 2013 at 10:51am

Hi PX4,

What is the current status of implementation of these codes in the APM firmware for PX4 / Pixhawk?

I would like to include this information in the Board LED and Sounds section of the wiki.

Is this working for both PX4 and PixHawk and as of which version 3.1rc1 for instance?

Comment by Gary McCray on September 16, 2013 at 11:17am

Question answered elsewhere, currently a work in progress final form yet to be determined.

My input for what its worth:

Breathing LED adds significantly to communication states in LED.


Use blinking to indicate an alarm or unsatisfactory condition. (Fail prestart (reason), Failsafe engaged - RTL - Land - Low Battery)

Use breathing to indicate states of readiness but not flyable (safety on, GPS not locked, not armed.)

Use solid colors to indicate flyable condition and maybe current mode.


Comment by Oliver on September 16, 2013 at 3:20pm

That low battery critical buzzer sounds exactly like my wife's cell phone ring which I automatically filter out (=:. Also the lights are much, much too complicated. Not in themselves, but because somebody is forgetting  that whatever device they are pouring their heart and soul into 24/7 is maybe just one thing among many to the end user. So the "breathing" green or quivering purple or whatever might mean something completely different on some other device that someone uses and thus become a possible source of confusion and distraction, the exact opposite of what's intended.

Gary's suggestions are a step in the right direction and would be great if everyone followed the same standard. But that's not the case. Therefore the best thing by far will be to let the user determine what alarms to set and with what patterns, colors, sounds, etc.

Comment by Dany Thivierge on September 16, 2013 at 7:41pm

I strongly disagree Oliver, leaving this to user preference is very dangerouns and will be very hard to document and support. Of course it's open source so you can change it but it will require that you know what you are doing. 

The big step forward is to get a small LCD on it that will tell us the exact state on the bench (as not really usable when in flight) and for the in flight by next year almost everyone will have the telemetry feed on either their radio or ground station laptop/phone/tablet... so it's getting there!

Anyhow, just my 2 cents but as a distributor I see a lot of people liking the DJI controllers ways to broadcast status. By all means it's not perfect but it a lot more feedback than the very small led on the current APM. Sounds/beeps is one of my favorite mod to clearly show when the APM is arming and disarming. Low battery alarms are also added to most builds. So the all in one I like.  Need to have the LED external to be able to see it from ground...


Comment by W. Joe Taylor on September 16, 2013 at 8:48pm

I agree with Dany.  For instance, flying the DJI I got used to the beeps and blinks, kind of like the old Simon Game I had as a kid 45 years ago.  Using a standard for the APM (which is the same as the PX4 / Pixhawk) like Gary said will make users learn the codes automatically after some learning curve, which will be shorter with the consistent beeps, etc.  Maybe enough cloners will also copy it so that a standard will come out of it.

Comment by Gary McCray on September 16, 2013 at 9:00pm

Actually my complete main mantra is keep it really simple, if it trys to report too many things the inevitable result will be that it is worse than nothing at all.

I would actually like it to be completely user programmable as Oliver says, but more expressly, for what information is included and what is not.

That way the user could set up a small but reasonable subset of warnings that works for him.

It is also fine to have a standard set of basic parameters that include the generally most important subset of warnings and standard sounds, colors, blinking, etc.

But the reality is we already have way too many possible notifications and if we don't give users the opportunity to select an appropriate subset for their use, we are doing them a disservice.

And for different uses, what would be important to know would change too.

I understand that if we were selling a Parrot or even Phantom that you want to make all the decisions for them.

This isn't that group, this is the bleeding edge, the people who are here know that give them the best initial setup that you can and then give them the tools to make as big a mess out of it as they want to.

Comment by Oliver on September 16, 2013 at 9:35pm

@Dany et al:

To re-phrase, a default set of indicators would be fine, but the option to modify or turn them off should be there too. Audio alarms in particular would be a deal-breaker for me if I couldn't disable them. Audio battery alarms have been around the fringes of r/c for ages and are unpopular, for good reason. I hope APM isn't going to start being loaded down with lame nanny gear of no value except to some vendor's lawyer.

Comment by Dany Thivierge on September 16, 2013 at 10:43pm

Oliver, again open source beauty, build it, mod it and make it what you like ! :) 

We will see how the mission planner evolves again for the PX4 and I am sure these options will make it somewhere for you and other to disable and tweak.  

Comment by Nicholas Witham on September 17, 2013 at 12:01am

Why not use a voice with words instead of the beeps. If people with a T 9x can add vocal telemetry to their hand units, then I guess we can add vocal warnings, maybe with some kind of add on?

Comment by Oliver on September 17, 2013 at 12:26am

Why not use a voice with words instead of the beeps. If people with a T 9x can add vocal telemetry to their hand units, then I guess we can add vocal warnings, maybe with some kind of add on?

I want Darth Vader with a nice Russian accent!


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