Replies to This Discussion

Permalink Reply by Vernon Barry on April 23, 2012 at 6:14am

Pictures say 1k words so here you go. I removed the 2 buffer ICs and then directly connected the Xbee IO pins to the boards IO pins. In order to remove the ICs, just get a bead of solder flowing that connects the 3 pins on each side, keep the iron applying heat and the entire chip will slide off past the pads where it no longer sticks due to the solder mask and leaves the pads perfectly open with a light tin. Hopefully, you can see the pin connections and then also see the two open pads where the ICS were removed. Sorry for all these mods from the original directions but the bottom line is that it works and it's proven. Again, to be sure, the 5 pin ICs are regulators, don't touch them, but the 6 pin ICs are the bufferes.

 

Permalink Reply by Dwgsparky on April 23, 2012 at 8:35am

HI Vernon

in my case this is a new setup and new xbees and adapters, if the adapter does not work then I will discuss this with the supplier for replacement before I start making mods like this. , If they normally work then why would we have to modify a new board.?

looks like another week with no data . just when I was getting somewhere.

 

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Permalink Reply by Vernon Barry on April 23, 2012 at 8:53am

My point is, LOTS of people have this setup not work stock. it's not necesarily a bad board. Thus, you really have 3 options in front of you. The forums are full of people who cannot get Xbee working.

1. Contact them and wait for a new board.

2. Buy the one from Sparkfun that also needs a mod and use it.

3. Mod your board and use my proven method that works.

Options 1 and 2 are going to cost you postage alone, time for waiting and option 1 could come back and still not work.

Option 3 works, costs you nothing than the time to solder.

I'm not trying to push you, just show you the facts I was facing yesterday on a Sunday wanting to fly my 2nd quad. Obviously I had a working setup on one heli  (using the Sparkfun board) and was trying to get the second one done using hardware I had paid for sitting on the bench not working (basically 1 step from the bin).  I have the same carrier, it did not work, would not work and has never worked. I made the mod that cost me nothing and now it works. I did a cost analysis before I touched the board and said via USPS, it was going to be $8 flatrate to send it, wait forever for it to reach California, and then maybe have the same part shipped back (no problem found) and still not work. Ordering another adapter from Sparkfun was even more money. Worst case, I screwed up the carrier and had to buy a new one anyway. Forums and spec sheets of the Xbee pro shows there is nothing wrong with directly connecting the pins. Further, it just plain works. I'm trying to give you the lowest cost fix. I understand your desire to "contact the manufacturer" but let's face it, that doesn't solve the problem you have on the bench in front of you. It will take you longer to call them than to make the mod. Maybe, there is some trick I never found and it's a setting or wiring issue, then fine, but if they even think about saying send the board back, you have more time and money than it's worth in even dealing with them.

 Yet another thread digging into level shifting and mods

http://diydrones.com/forum/topics/xbee-wont-work-with-esc?commentId...

Point being, lots of people have modded the carrier for the same reasons, it does not work with certain Xbees (some require pullups), and or level shifting jsut doesn't work.

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Permalink Reply by Ulrich Thiemeyer on April 24, 2012 at 2:17am

I have the same problem...

Isoldered two wires to the xbbe like you, but i did not desolder the two ic´s.

Is it necessary to disable them?

best wishes from Germany,

Ulli

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Permalink Reply by Vernon Barry on April 24, 2012 at 7:05am

Yes, you must remove the ICs. It's a buffer driver chip so it's either pulling high (5v or shorting the output to ground) Obviously, you cannot communicate if this is happening.

 

The orignal theory is that those ICs also have an inversion switch setup and thus the mechanical master and slav switch drove the buffer to reverse the TX and RX between the actual Xbee module and the pinouts.

The bottom line is that they are very much connected to the circuit and will not let the pins swing high and low like they need too.

Look at it this way, the board was desinged for many Xbee modules. Some only have 3.3 volt logic levels, some require pullup resistors, on and on. By putting a buffer, they assumed it would make it universal, however with Xbee Pro 900s, they seem to be hit or miss. Without some side by side comaprisons of the Xbee modules themselves and the boards, it's hard to tell which is the culprit. What we do know from the data sheets is the Xbee Pro 900s are 5 volt logic out anyway, which means we do not need the buffer-hence why they work with the Sparkfun module after it's crazy diode buffer (simple way of ensuring a 5 volt signal has a 0.7v drop to be somewhat in spec with 3.3 volt logic). A crude device but could be effective if we needed it. The problem is again, Xbee Pros are 5 volt logic and so is the ArduPilot. So if you put some 3.3 volt buffer logic in between the Xbee Module and the APM it's NOT going to work.

Again, just to be clear, this is all about using an Xbee Pro 900 not necesarily other modules. I cannot say it works with 2.4 Ghz although worth a shot. The problem again is logic voltage levels and if the module is 5 volt instead of 3.3 volt logic, then it appears the module is not compatible stock. But if your module is 5 volt logic, just make this mod and it will work.

Again, the hot tip (literally) to desolder the tiny SMT ICs is to add solder with the iron until a large blob is conducting heat to all the pins and then gentle pressure will slide the entire IC off the pads leaving them clean and not shorted together. I know it sounds crazy to add solder when trying to take somethinf off, but I have doen this hundreds of times. The ICs can even be resused later, they are not damaged by this process. It's not entirely different from what happens with wave soldering.

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Permalink Reply by Ulrich Thiemeyer on April 24, 2012 at 9:30am

Thank you very much for discribing. I will think abaut desoldering. In the past i made the same mistake like several users when soldering the xbee's. I put them together for soldering &)/$¥#% .
Because of that, the solder run through the pins. It is possible to move the bugs off, but will be difficult to reverse it. I will sleep about. Also the question if the xbee is working with the apm1 after the mod. I use the 2,4ghz module.

We will see. May be there is an other solution in future. But i dont think.

Thank jou very much,
Ulli

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Permalink Reply by Vernon Barry on April 24, 2012 at 10:02am

Sorry, I wish I had all the answers, but because there are so many possible versions of Xbee modules, without looking at the exact data sheets and then testing with some data probes it's hard to tell exactly the issue. The carrier is a good design, and works with most situations, but obviously at least 3 people cannot get it to work which is very bad probability.

I just kinda use this logic, that if I can pass a loopback test but still cannot talk with the APM, then it pretty much has to be a logic voltage mismatch. The only real solution is build your own buffer carrier or just connect the pins direct.

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Permalink Reply by Dwgsparky on May 2, 2012 at 12:37pm

Hi Vernon (and all the others who have helped. )

I sent the Xbee carrier back to the supplier and he replaced it with a new one that he tested before dispatching it to me, I fitted the new board and made no changes to the programs, wiring, comms or firmware and everything works correctly.. Data everywhere.

My xbee is now communicationg through the UART0/2 port with no solder links on the APM 2 and everything works..

I am very pleased with the proffessional and effiecient way that the supplier helped his customer to a success.

So a big THANK YOU to Dany at Canada Drones for a job well done., :) More purchases heading your way soon.

Dwgsparky

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Permalink Reply by Boris Matuschka on June 22, 2012 at 10:11am

Thank you Barry! You saved my day after struggeling arround with my xbee modules! thanks fpr your pictures!!!!!

Regards,

Boris

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