Battery voltage sensor without external hardware


I am using the Navio+ with a FrSky D8R-XP receiver. I would like to get a signal from the receiver on my transmitter when the battery voltage is low.

The first option that came to my mind (the obvious one) is to get a FrSky FBVS-01 and hook it up to my battery and receiver. But knowing that the Navio Power Module has also a voltage sensor, which can yield the battery voltage after calibration, I would like to get rid of the extra piece of hardware that is the FBVS. Is it possible to output a signal readable by the A1/A2 channels of the D8R-XP receiver with the Navio+ board ?


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If your trasmitter is a Taranis, this will be very helpful:

Hi and thanks for your input,

If I understand well, with this solution I need the converter sold by Airborne, which I would connect to the “digital data stream port” of my D8R-XP. If I only want battery voltage sensing I am then better off buying the FBVS, mainly because it’s cheaper and simpler to use (or am I wrong ?).
The idea behind my initial question would be for example to output a signal to the analog ports of the D8R-XP, the same way the FBVS does, but using the built-in voltage sensing of the Navio power module. Can the Navio output analog signals ?

Navio has no DAC, so it can’t output analog signal. If you get the converter you will have all data from the APM on your Taranis screen, so it is a good value.

Operating with analog signals and especially regenerating them is not a consistent way of handling data streams.

This is the main page I found which discusses the options and technical details:

(do not be confused by some incorrect references to FUC-1, it is only the FUL-1 adapter which is valid)

Most of the intelligent (processor based) FrSky MAVLink adapters I’ve seen assume you have an X series receiver with digital telemetry (SPort/SmartPort). For the analog D series receivers the traditional Pixhawk solution is probably the best unless the Airborne adapter also supports that (probably not if it already has a hardware inverter for X series). So specifically we’re talking about this:

See “D-Receiver setup” on that page. It’s actually simpler than the X receiver because you don’t need to invert the signal. You just need the FrSky FUL-1 adapter then.

I’ve actually got all three types: The FrSky adapter, Teensy and the components to make the self-made converter because I want to evaluate them all before choosing the best to build more drones with. I also built the Lipo cell monitor add-on. Regarding price, you’ll see other examples where people have found generic converter boards on eBay or Amazon. See the photos of what the user “epquilloy” made on that GitHub page. I myself found a pack of 5 generic TTL converters for a few euros, but too late (after I already bought the FrSky adapters and Teensy).

Teensy is way overpriced, the same as a Raspberry Pi. So I too was wondering if the Navio could be wired-up to do the same job as a Teensy. But because we always need a bit of external circuitry to do some voltage conversion or inversion we may just quickly come back to the native adapter cable being the best overall. It depends how good the software support gets, because currently the numbers of messages is much more limited in the native solution compared to the Teensy (and I guess also the Airborne adapter is better too).

Whilst were on the subject, for anyone interested in the native X receiver connection, it’s also possible to skip the SPC adapter by soldering the same black diode (the only device on the SPC board) across a couple of the pins on the FUL-1, which saves a lot of money and complexity! See the later photos, also by “epquilloy”. Seems to be the most popular solution and makes it almost the same price for X series receivers.

One last thing about serial/UART ports. You can put a splitter cable on UART ports for telemetry, but the problem then is without any intelligent device on the other end it will only subscribe to events/messages that one or the other device requested (it’s a lottery; something like whatever the last overlapping subscription/frequency message was, which devices often send at startup). Classic example is missing or too slow updating information on an OSD.

@ThoSc1 Code chief is right that our converters do not work with the D-Receiver as they stand. Not because it can’t be adapted but because we have no D-Receiver on hand to try and test the modification. If there is sufficient interest we can do it.

If you had a X-Receiver then yes it would be plug and play and the "Battery Low"messages as well as display of voltage measured by Navio would be available.

@CodeChief Regarding the UART splitter solution…we don’t think it is is viable at all even in terms of electronics much less in data.

@CodeChief: Also when making your choice for telemetry modules take into account what the packages bring. A teensy not only requires soldering which has its own costs but also does not bring the required cables and headers (servo and UART), which also do not have a trivial cost for unit prices. Our solution comes supplied cabling, ready to work. We are on backorder for the next 5 days though. We did not anticipate so much interest.

Paulo Neves
Airborne Projects

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