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Daniel Wee

My little NAV/OSD project - under construction

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With Daniel enjoying a well deserved few days off, allow me to take center stage and share with you the fruits of my labor this weekend.

As I mentioned earlier I've built the DragonOSD from scratch and have it running on a piece of perforated board at the moment. I had some issues with the GPS initially, but those were resolved quickly.

This weekend I finally got to play with the Allegro current sensor that came in last week. What was immediately apparant was that the circuit Daniel deviced had to go as that was more a amps-peak detector rather than a useful tool to check mAh consumed by the electronics.

Hence I modified the current sensor circuit as per the below noted schematic. Full range resolution is 50A, which now equals 3V3 output. That voltage is the maximum allowed input voltage for DragonOSD modules powered off of 3V3. The 5V version (which I'm currently still using) could handle 5V input, but this gives plenty of resolution already.

Revised current sensor schematic

12103.gif

Obviously the AMPSZERO, AMPMULT and MAHMULT had to be changed to be able to properly use this current sensor configuration. In order to calibrate it I used a variable bench power supply set to 13.60V DC and a 8.2-ohm 150W dummy load.

As per Ohms law the power draw from above load is: 13.60/8.2 = 1.66A. However the OSD, and GPS consume power as well. With everything connected the load increased to exactly 1.90A (~26W). Hence the AMPSZERO had to be set to correspond to that level with everything connected.

Total mAh consumed after 5-mins

12101.gif

Obviously the AMPMULT and MAHMULT had to be adjusted as well, which needs to be done over time. I did this by measuring mAh over 5-minute intervals. A load of 1.90A translates to 158mAh consumed over a period of 5-mins. Below you'll find the correct setting for the variables which are needed to properly use this modified current sensor.

Current sensor settings for mAh consumption

12102.gif

Next modification will be a slight alteration to either the code, or the values for the resistors for monitoring both battery voltages. They're both off by about 40mV, which isn't much, but why not make the effort of making sure they're spot on, right?

Cheers,

Sander.

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Wow. I started reading this a few weeks ago but became disinterested when I infered that it would have to be built yourself and programmed yourself. However, this weekend someone told me that it is being sold RTF. So, now I am really interested! Any news when Range Video will carry them? Or is it better for me to order from Intellegent Flight?

Thanks :)

-dave

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We wont be distributing the Dragon via usual channels for some time yet. We want to get the dragon website fully operational and with all the project/code sharing features we've been dying to implement before we even think about distributing them. We feel that the community we want to build around the Dragons is going to be vital to it's long term open source success.

So just order from IF, new stock due 3-4 weeks we are told by the manufacturing company. We've got a lot more than last time so hopefully they wont sell out so quick, and we plan to make more as soon as stock levels begin to run down.

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So with the new version coming out, can you please explain what other equipment we will need with it? For instance...

What type of power source?

Which current sensor should be used, and will it be plug-and-play?

Will the GPS be plug-and-play as well if ordered with the Dragon?

What other connections or soldering are required?

All of these questions have been answered for the 1.0 boards, but I don't know if it will be the same for the 1.1 boards. Plus, all the information out there right now is scattered throughout many posts and the user manual. It would be great to have all pertinent information placed in one spot. Less confusing that way. :)

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Yeah, hopefully. I'm sure all this information will make it's way into a new revised version of the users guide also. But it would be nice to have some of this info now, so we can plan accordingly.

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All of these questions have been answered for the 1.0 boards, but I don't know if it will be the same for the 1.1 boards. Plus, all the information out there right now is scattered throughout many posts and the user manual. It would be great to have all pertinent information placed in one spot. Less confusing that way. 

You mean a comprehensive feature list of sorts? Bullet pointed and with a short description of each feature for your viewing pleasures? Did I mention that in that regard I'm really a sucker for detailed pictures? Yeah, I'd like that too :rolleyes:

Cheers,

Sander.

Edited by ssassen

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What type of power source?

Which current sensor should be used, and will it be plug-and-play?

Will the GPS be plug-and-play as well if ordered with the Dragon?

What other connections or soldering are required?

We do have someone working very hard on the website for the dragon osd which is where all this info will end up :)

Power source: battery :P

seriously though, 2-3s should be fine (we have a bigger regulator for 5v now)

Current sensor:

We're getting a set of IF Current sensors specially made for the dragon OSD with a 0ohm resistor in place of the 10k. These will be completely plug and fly :)

GPS:

As always, our GPS have the correct connector installed as standard when ordering bundled :)

Soldering:

As far as i'm aware.. only the battery connector needs to be soldered to the board, and i'm going to add the option for a 2.54mm spaced header for this if people want it pre done for them. Personally, i'll be soldering a cable with deans to mine so that there is zero to no chance of the dragon coming unplugged in flight.

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I have just finished assembling the DargonOSD/BOB4 etc and on first powering up I seem to get three possible screen displays:

1. Just the 'waiting GPS data' message

2. The full data screen but without the satellite channel numbers and signal strengths, or GPS position data

3. As 2. but with 00.000000 for position data and the satellite signal strength data filled with only minimum values.

I assume I need to change the baud rate of the GPS as the data sheet default value is 4800 but what does the DragonOSD require from the GPS?

regards Peter

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Thanks for the info Mark. So I guess it's safe to power it from 3S lipo now with the bigger regulator? The current manual states 6V-16V input, but it sounded like it really wasn't a good idea to power it with more than a 2 cell lipo. Sounds like this has been improved though, which is a good thing because I use 3 cell lipos in my plane.

0 Ohm resistor?? Uhh, can't you just use straight wire?!? lol :D

BTW, I sent you a PM and e-mail last week. Did you get those? Haven't seen a reply yet.

Thanks!

Brian

Edited by twinturbostang

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Hi pseddon,

The DragonOSD board will be able to talk to the GPS module on either 4800 or 38400 baud. It will subsequently switch them over to 115200 baud which is what it normally works at. You do not need to change those baud rates. My guess is that you got the level converter resistors wrong. You need to give a bit more information about which design you built etc.

Daniel

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Thanks for the reply Daniel,

I had a look at the source code and realised that I do not have to change the baud rate as you do it in the software. However I still have a problem.

I am using a board from IntelligentFlight that I received about two weeks ago. I have wired it up as per the manual and am now getting intermittent Home Set screens (sometimes I only get Waiting GPS Data) when I switch on. I am using an EB85A and BOB 4 that I already had.

I am beginning to wonder if the leads to the GPS are too long - they are about 45cms long.

I have now left the system on for about 10minutes to see if I can get a lock and it is still saying Home Set, 137.0m.

Any suggestions?

regards Peter

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pseddon,

You sure you got the right wires going to the right pins? I know thomas uses a 5 or 6m gps cable unshielded no problems, he puts the GPS in his garden so he can track satellites when working on stuff. lol.

0 Ohm resistor?? Uhh, can't you just use straight wire?!? lol

Ever tried putting a tiny bit of wire between two SMT pads 0.2mm apart? And then reflowing it? With a machine?! 0ohm = safe and easy.

As to PM's my inbox is perpetually full here. I think i remember seeing an email, but didnt see any questions in it so didnt respond. *shrug*

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Mark,

Fairly sure I have everything wired correctly as I can see the GPS sending data at different rates. I have checked the supply voltages and they are all ok so it is pointing to the GPS being faulty - I will continue to check things out though and report back!

Sounds as if my 45cms wires should be ok then.

regards Peter

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Ever tried putting a tiny bit of wire between two SMT pads 0.2mm apart? And then reflowing it? With a machine?! 0ohm = safe and easy.

lol No I have not tried that. Sounds challenging. :)

As to PM's my inbox is perpetually full here. I think i remember seeing an email, but didnt see any questions in it so didnt respond. *shrug*

Ah, ok. My questions were in the PM. I will resend questions via e-mail then.

Thanks,

Brian

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Hi pseddon,

If you are intermittently getting the HOME screen, there is a chance that it is due to leakage from the monitor. Just a few things to confirm - when you do get the HOME screen, the GPS altitude should read 137m or so. If it does, it means that your connections are correct. If not then then maybe it's not right. That's the first thing.

Secondly, if you're connecting this to a TV, sometimes the leakage current from the TV will mess up the incoming data. If you have an LCD goggles or something, try that. It may work out better.

Thirdly, you still have not mentioned which board you are using. If you are building the 4012 board, then you will want to read through the threads really carefully because there were some changes to the design mentioned in there which relates to the GPS input section.

Daniel

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Hi guys and thanks for the replies.

I was trying initially indoors and then when to a glass roofed conservatory and still no change.

Tried everything again today but outside and with video goggles and the OSD started up correctly every time; so Daniel I think you are correct about leakage from the TV. I could also see the top line of the display properly which helped.

I left it outside to try and acquire some satellites and nothing changed - except my battery went flat! The combination of the temperature being about +7C and the attempts to get it working yesterday have probably caused it to lose charge quicker than I had expected.

Anyone know how long it might take for a first lock from cold start - my Ublox that I have used on another project took about 20minutes I seem to remember.

regards Peter

ps thanks again for the help I will keep you posted!

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Hi guys and thanks for the replies.

I was trying initially indoors and then when to a glass roofed conservatory and still no change. :angry:

Tried everything again today but outside and with video goggles and the OSD started up correctly every time; so Daniel I think you are correct about leakage from the TV. I could also see the top line of the display properly which helped. :)

I left it outside to try and acquire some satellites and nothing changed - except my battery went flat! The combination of the temperature being about +7C and the attempts to get it working yesterday have probably caused it to lose charge quicker than I had expected. :(

Anyone know how long it might take for a first lock from cold start - my Ublox that I have used on another project took about 20minutes I seem to remember.

regards Peter

ps thanks again for the help I will keep you posted!

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Hi pseddon,

Perhaps you should connect the GPS to a PC first. If you have the USB level converter, you can use that to test if the GPS is working.

Again, I ask, which board are you using?

Daniel

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Twin,

Sorry, this may be a dumpb question...

There are no dumb questions, only stupid answers, I am however holding my breath to hear the answer to this one:

Again, I ask, which board are you using?

Cheers,

Sander.

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Hence I modified the current sensor circuit as per the below noted schematic. Full range resolution is 50A, which now equals 3V3 output. That voltage is the maximum allowed input voltage for DragonOSD modules powered off of 3V3. The 5V version (which I'm currently still using) could handle 5V input, but this gives plenty of resolution already.

Revised current sensor schematic

12103.gif

Sander,

A very helpful post! I also just got the Allegro sensors and will need to build the circuit. Yours looks very good. Just to confirm, you're using 0.1 uF caps right? Ceramic ok? Sorry for the simple questions, I've been away from schematics for a long while.

Circuit still chugging along nicely?

BTW, I have an extra ACS755 LCB-050 so if anyone state-side wants it PM me your address and I'll put it in an envelope. Not that requesting from Allegro is hard or anything :)

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Anci3nt,

A very helpful post! I also just got the Allegro sensors and will need to build the circuit. Yours looks very good. Just to confirm, you're using 0.1 uF caps right? Ceramic ok? Sorry for the simple questions, I've been away from schematics for a long while.

Yes, 100nF (0.1uF) ceramic multilayer is fine. Do take notice that the connector pinout on my prototype is different than what IF uses.

Circuit still chugging along nicely?

Yes, I've actually stepped it down to 3.3 volt for the MCU and GPS which meant a further reduction in parts. If time permits I'll post an update about that later this week.

Cheers,

Sander.

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