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 LK8000 International Support
 Delta/Hang Gliders
 Proper vario + speedometer protocol
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ViktorPlacek
Pulcino

Czech Republic
11 Posts

Posted - 02/12/2012 :  18:23:30  Show Profile  Reply with Quote
Hello,

I develop acoustic variometer with speedometer for my MIO MOOV 300 and looking for proper communication protocol with LK8000.

Well, barometer/variometer for LK8000 is nothing new. A lot of para-gliders are successfully using it. But as a hang-glider pilot I want to measure an airspeed too (using Prandtl probe with Motorola MPXV7002DP pressure sensor with proper I2C 10-bit A/D converter). It allow me safer glider control and using of total energy variometer (tevar) algorithm.

Other paragliders are using LK8EX1 sentences for serial port communication. But this protocol cannot transfer airspeed information. I need protocol allowing me to transfer altitude and airspeed (optionaly vario and pressure).

Do you know which protocol would be suitable for my application? Transferring altitude and airspeed, but not GPS position. And still light enough for easy implemetation.

AlphaLima
Moderator

Germany
1990 Posts

Posted - 02/12/2012 :  18:43:49  Show Profile  Visit AlphaLima's Homepage  Reply with Quote
The V7 could be a good choice. I can send you a copy of the spec.
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Coolwind
Moderator

Italy
8957 Posts

Posted - 02/12/2012 :  20:19:40  Show Profile  Visit Coolwind's Homepage  Reply with Quote
PLKAS is the NMEA sentence for that purpose.
// LK8000 IAS , in m/s*10 example: 346 for 34.6 m/s which is = 124.56 km/h

PLKAS,346,[checksum]

This PLKAS is always managed, even while using LK8EX1.

Edited by - Coolwind on 02/12/2012 20:21:19
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ViktorPlacek
Pulcino

Czech Republic
11 Posts

Posted - 03/12/2012 :  16:49:04  Show Profile  Reply with Quote
This PLKAS sentence is exactly what I needed. Just waiting for pressure sensors incoming from China.

BTW. It has been a lot written about denying acoustic variometer implementation in LK8000. It has its sense as the altitude got from GPS is very inaccurate. The XCSoar implemented it. I tried to fly with it and it is really useless (unless you are 1980's chiptunes fan).

But I will have accurate altitude information from barometric sensor. If LK8000 would taken acoustic variometer implementation from XCSoar (maybe it is not so easy) it would greatly simplified barometric electronics. I would just sent instant barometric pressure (ten times per a second?) and LK8000 would make the rest - conversion to altitude, derivation with low-pass filtering (running average?), total energy computation with speed polar taken in mind, proper sound generation... Do you imagine, how easy and cheap would such barometer been?

Well?
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Coolwind
Moderator

Italy
8957 Posts

Posted - 03/12/2012 :  18:51:21  Show Profile  Visit Coolwind's Homepage  Reply with Quote
Why do you want to transform a flight computer into an acoustic variometer?
Acoustic varios are cheap, are accurate because they process data at 20hz, and they control sound in real time.
So while should we bother doing it?
If someone want to dedicate his time to this, experimenting is always welcome .
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ViktorPlacek
Pulcino

Czech Republic
11 Posts

Posted - 03/12/2012 :  21:56:43  Show Profile  Reply with Quote
20Hz? Well, it's quite a speed... Are you sure of this information? If it is true, then it would be really pain to ar.. to transfer barometric information to PNA. And more labor for PNA CPU to handle it.

Then, I will process all the measured data in electronics. Or if I would like to experiment with processing in PNA I will try XCSoar and refer here the results. Now, enough talking and start routing (PCB) - I hate this work.
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Coolwind
Moderator

Italy
8957 Posts

Posted - 03/12/2012 :  22:14:01  Show Profile  Visit Coolwind's Homepage  Reply with Quote
I know the minimum needed is 10hz, and 20hz is what a manufacturer is using if I dont recall it wrong.
We paint vario at 1hz. We may go to 2 or 3 hz, but the data must come "cooked" in any case.
Cooked means: averaged ("integrated") on a configurable time, which normally is around 0.5 to 3 seconds.
The point is that RS232 is an async transmission, and we handle incoming data in async mode of course.
So we are not in sync, by definition, to what the vario is sending. So there is no point in sending 3hz data, because when we process for the user (we show) the value, we are already 1 to 2 seconds late. Which means we are many, many sampling away from what a real variometer would say.

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ViktorPlacek
Pulcino

Czech Republic
11 Posts

Posted - 04/12/2012 :  12:54:54  Show Profile  Reply with Quote
Hey Coolwind, this is finally understandable (for me) and comprehensive explanation of the reason, why not implementing acoustic variometer in LK8000. I call this thread as finished. Thank you for the answers.
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DeltaGerard
New Entry

4 Posts

Posted - 28/02/2013 :  10:44:23  Show Profile  Reply with Quote
I have a question regarding to the NMEA sentence. Is it possbile to send any information, like heading (compass) to LK8000 using this protocol? Or is it limited to speed, baro etc.? If it's possible, would it require modifications to the LK8000 software to use the heading from the NMEA sentence?
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Coolwind
Moderator

Italy
8957 Posts

Posted - 28/02/2013 :  12:20:57  Show Profile  Visit Coolwind's Homepage  Reply with Quote
It requires modifications, we dont use the external heading so far.
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DeltaGerard
New Entry

4 Posts

Posted - 28/02/2013 :  13:09:07  Show Profile  Reply with Quote
quote:
Originally posted by Coolwind

It requires modifications, we dont use the external heading so far.



Thanks for the response, I have a microcontroller for a Quadrocopter that has accelerometers, compass, baro etc. I'll try to modify the code of LK8000 and try to get it working.
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