Hi together,

i want to use a D4R-II together with APM2, PPM and RSSI are no problem. What i want to connect as well is 

the serial port of RX and APM2 to send compressed GPS information over the FrSky data downlink to my antenna tracker. in principle i have that working, currently with an arduino pro mini evaluating an attached GPS sensor, compressing the GPS data and sending it over the downlink. So tweaking arducopters software to do that as well will be no big deal. I use NewSoftSerial with the arduino as it provides the inverted TTL signal, that is expected from the FrSky RX.

Question now is:

1) Can FastSerial in Arducopter 2.6 somehow be used for generating an INVERTED TTL signal?

2) Which Pins/Port should i use on the APM2 to connect the FrSky RX serial port?



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Hi All,

I have my telemetry stream working correctly with APM 1 telem output to an IO_board and thence to a FrSky D8RII-Plus Rx. The connection to the Rx is simply IOBoard D5 -> D8R-II Plus Tx port; the Gnd line is already common.

My Tx uses the Sky9x board but the software (ersk9x) is directly equivalent to the Er9x. Taranis uses OpenTx but again this should work similarly.

The problem with the GPS display is because the FrSky_Mavlink program for use with the IO_Board (or Arduino Pro Mini etc.) mixes up Lat and Lon - follow the FrSky_Funcs module through against the FrSky Telem Protocol. Curiously it is said that this mis-allocation works OK with the FLD-02 display. I can't comment on that but I do know that switching the functions in the program gives me the (almost) correct display on my Tx.

I say almost because as you will realise MavLink sends the GPS data as degrees.decimal degrees whereas the FrSky protocol uses degrees,minutes.decimal minutes.

To correct for this I modified the FrSky_MavLink program accordingly; in fact I went further and made the display format degrees,minutes.seconds - i.e a display of 5324.1465 means 53 degrees, 24 minutes, 14.65 seconds. The modified program modules FrSky_Funcs.ino and MavLink.ino are in the zip file appended.


Thank you Simon. I will take a look at those and update sources. 

Hello Simon, if I am not mistake, it was this thread : (Telemetry to Turnigy 9X (with FrSky FLD-02 Telemetry Display Screen) that had given me hope as I did a detailed follow up on the findings and did not hear anything back.  I know everyone is busy with other lives other than Quad Flying... (not sure why they would want another life?)

But that being said.... Here is what I found.... and posted a series of pictures to show it... (Findings posted on other thread

I will try again with Jani's How-To and post a recording for all to see.  I find it very helpful when posters can support their findings with a video or photo.  Its not that we/I don't believe you... its just a great reference for comparison.  ;-)

Stay tuned....

Jani - forgot to mention that I added the following variables to IO_Board.h

// new variables
static float      deg_dat = 0 ;
static float      dec_deg = 0 ;
static float      min_dat = 0 ;
static float      dec_min = 0 ;
static float      sec_dat = 0 ;
//end of new variables

This was simply to make the degree/minutes/seconds conversion in MavLink.ino more intelligible. You could reorganise the calculation and eliminate these.

yes i already noticed on those and added them. Also there were iob_ampbatt_A, cell_count, cell_numb, celV[], iob_lat_dir and iob_lon_dir values added.

well a bit OT here so we can continue on IOB thread.

Now that I was able to turn my self back to programming mode. I have been able to make some updates on IOBoard software. Also Simon bumped coding forward a lot.. Well that's how communities are working :)

After looking a bit more around I found that some people have cloned IOBoard codes to GitHUB. That's great.

Anyways here is small update that fixes several problems on earlier MAVLink/FrSky software. This software works really well with Taranis/er9x and openTx based radios. FrSky TLD-02 display still have some problems but those will be sorted out later.

Many things are currently static on this but they will hopefully change too.

Be free to distribute this to your friends and let us know if/what problems there are.


I just  bench tested the new hex and I am only getting X,Y and Z acel values on my Taranis. altitude speed, etc. are still not functional. pretty much the same as before for me.

I just flew with this configuration. GPS is being displayed accurately now on my FrSky Taranis.  I tested the same APM 2.0 with Arduplane 2.74b.  I got Lots of info, except the ALT and SPEED (maybe this is because of the v1 mediatek GPS?) . this is coming along really nicely. Thank you. if you want to continue in a diff thread please post a link. Thank You for all your work. side-note: (distance seemed off by 20 feet but it was rock steady once i accounted for the differential).

Another day working on this IOBoard Solution and unfortunately no luck.
The good news, is that I do get alot of information posted to the screen but that was there before as well.  The bad news is most of it wrong.

I placed the latest hex file and was not successful and then I placed the original hex and was able to get a GPS Coordinate that was correct but then it would change periodically (not stable)

The one thing that did work was the Cell parameter with the Battery Voltage of the Pack and number of Cells.

I will wait to see if any new advancements change over time but I have created a wiring diagram along with a video showing the results in APM along with the Radio.


p.s. Thanks for the hard work and I wish I could program to contribute.  I honestly put 6-7 hours on it today trying all sorts of things.

The VIDEO...


What all you have connected on telemetry port or just IOBoard?

Have you tried to use ioboard with telemetry modem on same time?

I will create new post for future development of this board as here it's a bit Off Topic :)

Morning Jani, or afternoon where you are?

I originally had the IOBoard with the Telemetry Modem.  I recently just tried the IOBoard alone as per your thread message. I have removed my IOSplitter just to rule out any issues.

It's now 1am in here... Bangkok is GMT+7

But yeah that's correct way to do it. On my desk there is just similar combination now. APM2.5+, Telemetry Distro board, RFD900 modem and IOBoard. From IOBoard I have 3 cables going to FrSky D8R-II Plus and FTDI connector has 4 pins to telemetry distro board. 

Btw i made several bug fixes on v0.3a software

Anyways, let's move all MAVLink/FrSky/IOBoard related discussion on it's development thread at here


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