Frsky XJT-Lite

Like B&Q for homebrew radios
MaxZ
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Frsky XJT-Lite

Post by MaxZ »

I have acquired a Frsky XJT-Lite module, to fit onto my Taranis X-Lite Pro transmitter. My main purpose was to have the capability to use the cheap D8/D16 protocol receivers for sale by a well known Chinese webshop.
Most of those offerings do not mention anything special about the protocol-version, but at least one mentions that only the first generation of those protocols will work, not so for the second and third generations.

Checking the Frsky website to see what is available for this XJT-Lite module, I am reading that I can flash two different firmwares, V 1.0 (labeled as "Historic) and V 2.1.0.

Any experiences anybody?

I also have read somewhere that you can use this module for conversion of vintage trannies, so it must have a ppm input connection, right?

Cheers,
Max.
wookman
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Re: Frsky XJT-Lite

Post by wookman »

There is lots of FrSky info on the RCM&E forum. https://forums.modelflying.co.uk/index. ... /76-frsky/
Basically if you are running V1 firmware on your Tx then your rxs need to be running V1.
If the tx is running V2 then so should your rxs.
The firmware is available free on the FrSky website.
You can't have too many gliders. You can have too little time.
Pchristy
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Re: Frsky XJT-Lite

Post by Pchristy »

The versions only apply to D16. There was only ever one version of D8. However, D8 no longer meets EU regs, and can only be legally used by "grandfathered" equipment.

--
Pete
MaxZ
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Location: Boskoop, Netherlands

Re: Frsky XJT-Lite

Post by MaxZ »

Thanks for the info guys.

Cheers,
Max.
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Phil_G
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Re: Frsky XJT-Lite

Post by Phil_G »

Pchristy wrote: 27 Nov 2022, 13:05 The versions only apply to D16. There was only ever one version of D8.
There were two D8 versions Pete, when D8 was first introduced as version 1 it ran for a couple of years, then they introduced V2, definitely two versions.
At the time I was quite friendly (in the net sense) with Rob at Giant Cod and had hundreds of V1 D8 receivers to update to V2.
It was over 10 years ago, I cant remember but I'm pretty sure I did a batch for Richard at T9 too.
I kept a V1 for testing and I probably still have the files somewhere :) My reward for this was to keep a few D8 receivers which I'm still using :D
Heres one pile of many undergoing surgery:
Attachments
d8_v1_to_v2_updrades.jpg
MaxZ
Posts: 330
Joined: 31 Jan 2019, 11:48
Location: Boskoop, Netherlands

Re: Frsky XJT-Lite

Post by MaxZ »

Hi Phil,

This is the receiver I am contemplating to buy: https://www.aliexpress.com/item/1005002 ... bq9mBwvoRN

Read the warning in red, it says I should use the “first generation D8/D16 protocol”. I am guessing/hoping that this is the same as the “historic V1 version” firmware for my XJT-Lite module.

And I am hoping it has a ppm input, so I can use it for a vintage Tx conversion, though I am not envisaging one in the near future.

Cheers,
Max.
Pchristy
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Re: Frsky XJT-Lite

Post by Pchristy »

Interesting, Phil! All the D8 receivers I've bought have always been exactly the same!

The first FrSky gear I bought was a "hack" module with a V8 receiver (non-telemetry). That module (V8/D8) is the one in my Ace single-stick Tx - the one I was flying at Ponty this year. I subsequently bought a number of D8 receivers and all have worked perfectly, not only with that hack module, but also my Taranis, X10S and a recently acquired RadioMaster T16. I have never come across an incompatible D8 system!

I'm just trying to remember when I got that original hack module. I guess it must have been around 2011 - certainly it was before I was able to get hold of any D8 receivers, only V8 seemed to be generally available when I made my initial purchase!

However, I am quite happy to stand corrected! :D

--
Pete
Martin
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Re: Frsky XJT-Lite

Post by Martin »

There was a later update, available on the FrSky website, for some D8 receivers - I flashed a few of my own - but it didn't alter the protocol, merely the frame rate for outputting CPPM signals.

This was at a time before things like SBUS had been invented, so we used CPPM (combined pulse position modulation) to output multi channels from the receiver down a single cable into our drone flight controllers.

The signal was exactly the same as the buddy box signal that connects transmitters - a train of narrow pulses, with the time separation between adjacent pulses indicating the position of a channel. It used the same nominal 1ms to 2ms time that is fed (as a varying pulse width) to our servos. Some of the FrSky receivers could be switched to output that signal on one channel by fitting a small link that shorted two of the other channels together. The D4R-II was the most commonly used. When it was working in CPPM mode, it output eight channels of data, even though it only had four output connectors for working in its normal (servo) PWM mode.

The problem was that the default frame rate was one frame every 18ms - and that meant that with all eight channels, all at their maximum 2ms value, the 'marker pulse' that separated one frame from the next was indistinguishable from the gaps between the normal channels pulses - you just got a continuous train of narrow pulses, all separated by 2ms from each other.

It didn't really matter, because the chance of all 8 channels being at their maximum (2ms) position at the same time was virtually zero, and even if it happened briefly, as soon as one channel reduced back to something shorter, the flight controller could lock onto the marker pulse once more. Allegedly, certain flight controllers would freak out and stop responding, if you fed them the 'killer signal' - but I never saw that happen myself.

Once the problem became known, FrSky released an optional patch for those receivers, that slowed their frame rate down to 22ms. That corrected the problem because even when all eight channels were at their maximum 2ms, the marker pulse was still 4ms long.
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Phil_G
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Re: Frsky XJT-Lite

Post by Phil_G »

Your D8 receivers will all have been V2 Pete, V1 and V2 were completely incompatible, control and telemetry. When V2 was annouced we caught most of the UK stock before they were sold. By then Frsky themselves had already switched to V2. I flashed a lot of D8 receivers for Giantcod & T9. Having made the change, subsequently Frsky never referred to versions or to any update to D8 - like it hadnt happened! I was on Frsky's beta for V8 and D8 :)
I havent found the files yet but here's where it was discussed (in 2013, a year after its release):
https://www.rcgroups.com/forums/showthr ... st25555412 (and a few prior posts)
Martin wrote: 28 Nov 2022, 18:23 There was a later update, available on the FrSky website, for some D8 receivers - I flashed a few of my own - but it didn't alter the protocol, merely the frame rate for outputting CPPM signals.
Thats right Martin, that was a minor release some time after, I have the frk file here dated 11/03/14.
The V1 to V2 update was a major D8 protocol change and mutually incompatible as you can see from Frsky's document attached :)
For some reason this update seems to have been swept under the carpet, it doesnt even get a mention in the RCG "History of Frsky" thread :)

Heres a Frsky document which confirms my recollections:
Upgrade How-to_D8R.pdf
(172.83 KiB) Downloaded 77 times
Pchristy
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Re: Frsky XJT-Lite

Post by Pchristy »

Hi Phil,

I was just wondering how I never came across it!

Perhaps the reason I was unable to get hold of any D8 receivers when I bought my first Tx module, was that they had all been held back for updating! It does sound as if very few V1 escaped into the wild!

--
Pete
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