Author Topic: Serial logic levels for Funkwerk TRT800 Mode S txpdr  (Read 9736 times)

flying_john

Serial logic levels for Funkwerk TRT800 Mode S txpdr
« on: December 07, 2015, 12:27:14 pm »
I wrote to Funkwerk technical to ask what their serial data expectations were on the RxData line in to the Mode S transponder. It seems there is no handshaking and they will parse an incoming data stream for NMEA sentences.

Interestingly they said it was at TTL + - 5volt serial data levels and not full RS232 (12v). so my question is: Does the Pi output TTL +-5v serial data on its USB port or is it only 0 - 3.3volts? (or some other).

If + - 5v then the need for an RS232  level shifter goes away and one could chop about a standard USB lead and find the Pi TxData out and use that as the data source for RxData in to the Txpdr.

Anyone know ??

John

AlanB

Re: Serial logic levels for Funkwerk TRT800 Mode S txpdr
« Reply #1 on: December 07, 2015, 12:46:59 pm »
If + - 5v then the need for an RS232  level shifter goes away and one could chop about a standard USB lead and find the Pi TxData out and use that as the data source for RxData in to the Txpdr.

Anyone know ??

John

John

USB and RS232 are two different standards and, if I'm reading you post correctly. simply using the Tx pin on the USB port to drive the Rx in port on the Transponder is not going to function. It's not all about the volts..

You would still need the USB to RS232 converter. Its not unusual for the RS232 voltages on an interface to be +/- 5v specified as the tolerance in the standard is a little flexible in implementation.
Europa XS Mode-S ADS-B out enabled.

Admin

Re: Serial logic levels for Funkwerk TRT800 Mode S txpdr
« Reply #2 on: December 07, 2015, 12:54:05 pm »
Hi All

You will need a USB/RS232 converter lead, plenty of these on eBay, but do not obtain an RS232-TTL lead these will not work.

RS232 provides +/-12v, RS232 provides 0v/+5v, but the real issue is that RS232-TTL uses inverted logic, so it is not only the voltage level, but also a logic1 translates to a logic0.

Thx
Lee

flying_john

Re: Serial logic levels for Funkwerk TRT800 Mode S txpdr
« Reply #3 on: December 07, 2015, 02:14:28 pm »
O.k - thankyou experts.

Supplementary question , if I wanted to implement RS232 conversion within the pi case, how would I tell the Pi (Paw) to send out data for the transponder using say a Max232 board connected to GPIO.

I want to try and avoid another cable hanging across the panel and this way I can just have a screen single wire running from Pi to Txpdr.

Thanks

John

Sierrakilo

Re: Serial logic levels for Funkwerk TRT800 Mode S txpdr
« Reply #4 on: December 08, 2015, 04:49:02 pm »
Likewise to John..... was hoping for a simple cable from Pilotaware to my TRT800.  ( already got a input wire to the 15 pin plug on the Txpndr )

scsirob

Re: Serial logic levels for Funkwerk TRT800 Mode S txpdr
« Reply #5 on: December 08, 2015, 06:04:50 pm »
I wrote to Funkwerk technical to ask what their serial data expectations were on the RxData line in to the Mode S transponder. It seems there is no handshaking and they will parse an incoming data stream for NMEA sentences.

Interestingly they said it was at TTL + - 5volt serial data levels and not full RS232 (12v).

Ehh. Wow. I asked them back in 2011, before I hooked up my true RS-232 Garmin GPS35HV. Mr. Thomas Kapelar told me the input was true RS-232 levels. I have had it hooked up ever since, and it works just fine. My flights show up on FlightRadar24 and I have received the occasional question why my toy shows up amidst the 'big boys'.

Rob

flying_john

Re: Serial logic levels for Funkwerk TRT800 Mode S txpdr
« Reply #6 on: December 09, 2015, 04:47:23 pm »
It does seem that Funkwerk are telling different things to different people. I just received this from them:-

Hello John,
attached please find some information regarding ADS-B.
If it has V4.8 you don´t have to send it to us!
If you want to send it – you will get SW5.2 and MOD11. But this will cost 250,00 excl. TAX.
And this is not necessary because 4.8 is enough.
I hope I could help you and wish you a nice day!
Mit freundlichen Grüßen / best regards.


This is after they told me the unit will accept RS232 at either +/- 12v or +/- 5 volts, so am guessing  they use +/- 5v internally and limit the input signal swing so that  +/- 12v  is clipped.


SteveHutt

Re: Serial logic levels for Funkwerk TRT800 Mode S txpdr
« Reply #7 on: December 09, 2015, 05:17:42 pm »
Hi John,

They may be confusing ( or not understand the detail of) :
  • Starting to support ADS-B ( v4.8 )
  • Properly supporting ADS-B with uncertified GPS with no bugs ( v5.3 ) - as per statement given to me
If you did not mention uncertified GPS or they missed/misunderstood that fact then I would hope that may explain their error.

I spoke on the phone with their Product Manager to absolutely check that his 'atleast v5.3' statement was correct.

It is interesting that they say an upgrade would be to v5.2, not v5.3. That does seem strange.

I will try to contact them to ask them to stop giving out false information. Unfortunately the Product Manager chap has gone off on leave until January as he is moving house.

Steve
Steve Hutt


bnmont

Re: Serial logic levels for Funkwerk TRT800 Mode S txpdr
« Reply #9 on: December 09, 2015, 09:18:49 pm »
It does seem as if Funke are giving various replys to enquiries regarding the TRT800.
My unit has been at Mendelssohns for bench testing following some concerns I have regarding power output/transmission range etc.
This transponder took part in the Nats trial and I received back from them an email saying output values were good.
I also used PAW to log the adsb and got Sil=0

Dan at Mendelssohns enquired about software upgrade for ADSB out, his email and the reply from Funke are attached. Admmitedly no mention was made by Dan of it being an uncertified GPS source, but reply from Funke does mention NMEA at 4800 baud which is the setting I used for the uncertified gps trial.

Confused!

SteveHutt

Re: Serial logic levels for Funkwerk TRT800 Mode S txpdr
« Reply #10 on: December 09, 2015, 09:56:45 pm »
Just to be very clear, the v5.3 requirement was not to do with ensuring output of SIL=0 & SDA=0 - earlier versions did do that - it was to do with bugs in the processing of the GPS data. That is, intermittently outputting erroneous position data. That is what I was told by their Product Manager. My suspicion is that their Tech Support are not au fait with the subtleties involved in all this.

Steve
Steve Hutt

ianfallon

Re: Serial logic levels for Funkwerk TRT800 Mode S txpdr
« Reply #11 on: December 11, 2015, 10:15:45 am »
Hmmmm - all a bit depressing!

SteveHutt

Re: Serial logic levels for Funkwerk TRT800 Mode S txpdr
« Reply #12 on: December 11, 2015, 11:05:39 am »
Yes, it is a shame. I emailed Funke yesterday asking if they could ensure their tech support team were briefed on the v5.3 requirement for uncertified GPS support and to ask that they confirm whether enquiries involved uncertified GPS before giving out advice.
Steve
Steve Hutt

ianfallon

Re: Serial logic levels for Funkwerk TRT800 Mode S txpdr
« Reply #13 on: December 12, 2015, 05:28:23 pm »
Probably a bit academic but does anyone know if they didn't conform to 'good' specs or if the specs were too vague or arrived late(r) ?

If the former then arguably they should give us free upgrades as it was not fit for purpose. If the latter then I guess we just have to suck it up  :(

scsirob

Re: Serial logic levels for Funkwerk TRT800 Mode S txpdr
« Reply #14 on: December 12, 2015, 07:36:39 pm »
My guess is they had some bugs in their older firmware. I run V4.8 and when I look at my flight track on FR24, every now and then there are some odd data points. It looks like it transmits an old coördinate from the track I flew, and then returns to the actual track. Not some random output, but something from a few minutes ago.

As for them picking up the tab for a free upgrade, I wouldn't hope for much. There are dozens of AD's for engines and planes that arguably are a design or quality control defect. Many times it is the owner paying for the mandatory repair.

Rob