190 replies to this topic

[jparisse]

Thomas,

The realtime GPS function is now part of Google Earth Plus. One can pan, zoom and tilt cached data off line which makes this a great program for moving map. One can even tilt the map to near horizontal to see a virtual forward view as the plane flys around.

As far as the modem: I understand completely. I'd be willing to kit and sell this modem if dzl is willing to part with the source code. I'll trade him Tesla coil parts. ;-) I ordered the programmer, software and a couple of chips so I should be able to whip this up next week.

Tesla: 1.5 meters is not bad for the power you were able to use (I'm guessing 8kW). We're getting ready to run the 13M this summer to make 20 meter arcs for an outdoor music festival in Seattle.

Jeff

[ThomasScherrer]

Google:
>cached data off line
aha ? so I can save the area I will go flying in ?
and then I dont need to be online later ?
my google is not the plus, darn..

More Telsa stuff:
uha !! 15m WOW !,
I was a bit worried when some flames came too close to DZL !
when he was adjusting the resonanse caps at full power,
he is a bit hi-voltage crasy :-) know them dudes with too much hi volt experiance, always stay 2m away from them, with one hand in the pocket !
we only had 16A x 400V x 3 phases as input, variable DC power with huge vario-trafo. http://dzl.dk/projec...psu2/index.html
and more here: http://dzl.dk/projec...psu2/build.html
it is actually my on the pictures and dzl behind the cam.

Modem:
I use two STK500 kits and a few ATAVRISP-MK2 and debuggers,
to test the modem sw performance here in my work-shop.
right now for protection, the audio phase needs to be right !
see the switch om the TX side, the TX AVR actually outputs a positive and a negative phase at the same time, use the positive phase if your radio link have no inverting audio function,
my 2.4Ghz video/audio link inverts the audio channel,
so that is why I asked for this extra feature.
it could have been made on the RX side, or also automatic detect and repair,
but to keep things simple and to be ready fast, I think it is ok to have it like this.

Edited by ThomasScherrer, 24 February 2007 - 02:32 PM.

[Mr.RC-Cam]

Thanks for sharing the modem project!

[jparisse]

Thomas,

Thank you also for the videos! I love seeing other people’s high voltage laboratories. The best part was watching how the high voltage experimentation was bothering the two guys trying to watch football on TV. Very nice diode array too.

I’m gathering parts for the modem project. I’m sure I’ll have hundreds of questions but I’ll keep them to myself. I’m learning FSK with some help from local engineers and hope to write my own code for the BasicStamp someday (yes, don’t laugh, I’m new to microcontrollers – I usually make my electrical connections with a large box wrench). I’ll keep this thread posted on my progress.

Thanks again!

Jeff W. Parisse
Director, kVA Effects
www.teslacoil.com

[jparisse]

Progress

So far, still no luck. I'm getting digital out but it is not the same as digital in.

I switched to external crystal oscillators to rule out clock problems. Next, I'll build in a pot to the output side of the TX and input side of the RX to adjust/match gains.

Jeff

[jparisse]

Changing R3 in the TX to a pot (to boost gain) worked to produce resonable looking digital on the RX out. It is inverted (and changing phase on TX does not change phase on RX) so I will invert with HW to a "proper" signal. Not seeing the source code, I'm not sure if the signal can be inverted in SW.

Anybody still with me on this one?...

Jeff

[jparisse]

I works over a wire... some of the time. Over a RF link?... I don't think so.

I've hit the time/money wall. I give up. I'll be gettin' a Maxstream.

Jeff

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[Mr.RC-Cam]

That is sad to hear. I wish I had the time to proto the modem chip set and help out. But, my schedule is hampered by the proverbial time/money wall as well.

[JMS]

Still I give you two thumbs up for the effort! Never give up on any new visions and perhaps success down the road!

[jparisse]

I usually succeed at the things I set out to do. Not always, but usually. This was a great exercise because; 1. it rekindled my electronics hobby (at least at the discrete part level), 2. I learned a thing or two about AVR microprocessors and I have a couple of leftover ATTINT2313s with which to play and 3. I found that it is easy to underestimate the difficulty of this particular task.

I talked this project over with some friends in the aerospace industry here in El Segundo. I seems generally accepted that cramming 4800 baud down a 10kHz pipe requires a more robust encoding and error correction than plain Manchester code will allow.

Thanks for everybody’s help and especially your kind words JMS!

Jeff W. Parisse
Director, kVA Effects
www.teslacoil.com

[ThomasScherrer]

now the page have been updated :
http://dzl.dk/projec...odem/modem.html
please also see this:
http://dzl.dk/projec...rrer/index.html
this is just a quick mockup in both ends to prove the function,
I have added attenuators and dummy loads to the radio link so I could simulate bad/poor/dropouts and the serial downlink works fine and resync fine.
so now I am happy and will newer be loost again.

I have no idea why Jeff could not get this fantastic thing working.
1. check your audio signal input not overloaded ?
2. check rx side audio looks nice symetric ?
3. check invert/not
4. serial input from GPS must have some breaks sometimes
5. only 4800 baud input/output is accepted.

Edited by ThomasScherrer, 28 March 2007 - 05:38 AM.

[mieczotronix]

that's brilliant! I am really impressed with your skills.
Could you tell a little bit about your source code (if you're not going to publish it)? What kind of filtering/processing on the received signal do you use, if any? Do you measure frequencies by measuring pulse widths only? Ie was it as straightforward to do as it now seems or you've had to fight with something a bit longer?
I'd really like to learn more details on your solution, since sometime ago I was thinking about doing this myself, but got discouraged by an older colleague, more experienced in electronics who said this isn't easily doable ant pointed me towards mx614.
Do you generate a digital waveform in modulator? and what is the invert switch for?
BTW The idea with pocketpc is also brilliant. I wonder why I have not thgought of it until now!

[ThomasScherrer]

well as I mentioned erlier the sw is not made by me,
all I did was to encurage the right skilled person to solve the puzzle,
he is dzl.dk one of my good pals,
we often freaks out making crasy electronic projects.

the whole pointe in digital over an audio line that is AC coubled:
you need a signal stream with zero DC component,
then the rest is quite simple phase lock and invert.
the source will not be released for free !
the project is allready free to DL as hex, maybe it should not have been like that,
since it will maybe soon be sold as ready made units.

but until then I will be happy to hear more from Jeff, I also would like to understand why it did not work out for him,
if any other have the HW and programmers, please test this for me/us.

The invert could have been made in eny side of the signal,
the phase shift is made negative, so if the audio signal is inverted (quite normally)
the inverted output must be used, so the RX decoder can find the phase shift.

To resync all serial lines need a pause or delay now and then, also required on RS232 signals, else you can not find the start bit again.
on a wireless system this is so much more important, since glitches will happen
now and then on all radio links, a good system is one that can handle this with no or low notice to the user.

[mieczotronix]

If I have enought time (I'm in the middle of big job right now), i'll test it. What are the fuses? 8MHz internal clock?

[ThomasScherrer]

the fuses:
8MHz internal clock
no div8
bor 1.8V

I suggest double checking not to drive the audio input too strong,
I have seen distortion that craped it up,
and if I run my TX module for a while with no wind and in direct sunlight,
it overheats and audio channel starts to fail, but when colder it works again,
hopefully my new tx gear will not suffer from that,
but ok normally planes fly, and are not placed for 5 mins in direct sunlight with no wind at all.

maybe its possible to add some sort of lowpass (rc) filter on the RX side also,
maybe that will improve it futher, I will see if it makes any difference after the test flights.

JEFF ?!?
are you back ? still nu luck ? I really want to know why and what happened.

Edited by ThomasScherrer, 28 March 2007 - 02:09 PM.

[ThomasScherrer]

Latest info:
I have been out flying again the whole day,
the modem works for me, if I have video I have nice action on my PDA navigator,
I dont get lost anymore and are not affraight of it.

only issue is the video tx/rx system has a lack of isolation from audio to video,
so I can see weak stripes on the picture from the data,
I dont know if it's the tx or rx side that generate the problem,
and it was so weak i did only notice it when looking at the video clips at home,
out at the field with action and sunlight in the PC, I dont see the stribes.

[Mr.RC-Cam]

so I can see weak stripes on the picture from the data

It's a problem that has been reported before when strong audio is used. Audio amplitude and bandwidth contribute to it. Try minimizing the amplitude that drives the input of the Tx. If square waves drive the audio, then try filtering them a little bit. If that does not solve it, then the modulation freq would need to be altered.

[ThomasScherrer]

allright I will, I am driving it close to clipping and at 5khz rounded edge square waves, so I am using my full 7khz bandwidth of the audio.
I can halve the amplityde with no problems.

Still no info from Jeff, anyone else playing with this modem ?
I was really happy about it, I used a PALM PC program called ODGPS, it can navigate to any point on earth, and make waypoints and record tracks you fly.

[jparisse]

I'm Back!!!!

While troubleshooting another project, I found out that the modem I was using was RS-232! So, I placed a MAX232 on it and THEN plugged it into DZL's modem and WALA!!!! The thing works GREAT over a wire but I still have to impediance match it to work with my TX/RX.

The giveaway was the TRIANGLE waves I was seeing.... they are supposed to be square.

Anyway... I'll be working on the analog stage to get it to work over my radio.

Jeff

Thomas... nice work on the OSD flying wing!!!

[ThomasScherrer]

allright Jeff is back !
ok you need to know the max drive level of your TX side,
check with a scope on the RX side and adjust the drive level a bit under 100%
if stribes and crud on the video try to go down to 50% or 75%.
on my TX 1vp is 100%.
the input impedance must also be known, or simply do as I did, use really low ohm value components for the filter and signal attenuator.
The TX side pulse shape must not be triangle, but square with nice rounded edges.

On the RX side I did not even add a filter to remove the hi frequency noise,
if I do that, it maybe will work a bit better on weak signals.

if your audio link has 7-10Khz bandwidth, the RX side signal will look almost the same as the tx side, square with rounded edges, the dutycycle must also look like 50/50% if all is perfect tuned, mine looks like 60/40 or even worse, but still it works.

I would like to know about what TX and RX units types you are using ?