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Old Mar 28, 2010, 02:31 PM
Never enough RC time.
jakesterama's Avatar
Joined Aug 2007
72 Posts
Well I seem to have all the pieces to the puzzle, but I can't bring up my nerve to try it

A9 side -
http://www.rcgroups.com/forums/showp...7&postcount=21

Module side -
http://www.rcgroups.com/forums/showp...&postcount=564
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Old Mar 30, 2010, 12:48 AM
Never enough RC time.
jakesterama's Avatar
Joined Aug 2007
72 Posts
Well I hooked up the Aurora 9 tonight, but no success. While holding the bind button, and tapping "Yes" to transmit on the A9, the LED on the module quickly blinks. After that, nothing happens. No bind, no control. Similar to this - http://www.rcgroups.com/forums/showp...postcount=1144

At first I thought it might be due to the discrepancies between pins 3 & 4 on the module. Sometimes they are defined as ground, or RF sense, or even not connected, etc. I opened up the module and found them to be internally connected, so that doesn't matter.

Second hypothesis was that maybe the supply voltage was indeed an issue, but I can confirm that V+ is ONLY passed to Vin on U1 which can be anywhere from 3.8VDC to 20VDC.

Now I think removing R2 may have something to do with it. To me it looks like a pull-up resistor. Given that it is meant for a Futaba radio, it is expecting negative shift PPM (signal is normally high and is pulled low for pulses) so if you were modifying the module to work with a positive shift system I can see the need for removing this resistor, but the A9 allows you to choose pos or neg shift, so I can't see how this would make any difference.

Good news is nothing turned into smoke, and the stock module works just fine.

Anyone have any ideas or can tell me if/why removing R2 would help?
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Old Apr 01, 2010, 01:46 PM
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Sunnyvale, CA, USA
Joined Apr 2000
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The ppm shift is nothing to do with the polarity of the ppm logic sigal. It sounds like the logic is inverted so try changing the shift selected in the software.

Oh, the Tx is set to ppm righ?

Lay off the bind button unitl you can power up and see a clean orrange light on the module. When you are at that stage try powering up in bind.

If the module has power and a ppm stream the right way up it should work.

The only reason for rmoving the pull-up would be if the Tx is providing an active drive through a resistor in which case the pull up will simple force the stream to look like a "1" continuously.

Can you look at what is happening on a scope?
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Old Apr 02, 2010, 05:54 PM
Never enough RC time.
jakesterama's Avatar
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I can verify that the module is expecting negative shift PPM and that the A9 is outputting it. Just for giggles I tried positive shift PPM and it didn't change anything.
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Old Apr 02, 2010, 07:22 PM
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I believe the R2 was because of voltage on the EVO...7.2 volt battery......Also the EVO also has neg/pos select
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Last edited by CAT Power; Apr 02, 2010 at 08:11 PM.
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Old Apr 02, 2010, 11:34 PM
iPhly R/C with iPhone
iter's Avatar
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I too am trying to figure out resistors in this module. (here: http://www.rcgroups.com/forums/showthread.php?t=1219407) I notice that I can make the module work (without desoldering R2) if I hook a 330 Ohm pulldown resistor between ground and PPM line. This does look awful small resistance for a pulldown.

Ari.
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Old Apr 03, 2010, 11:35 AM
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Joined Nov 2009
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If you were trying to pull down a 3.3v line (not exactly sure what the voltage on that line is) with a 330ohm the current draw will be about 10mA. As long as the IC / circuit generating the PPM signal can source more than that you should be fine.

If it is 7.2v, then the current would be about 22mA. That may be approaching close to what a microcontroller can source on a single line. Though I really don't know what is generating the PPM signal you are pulling down.

Also, if R2 is a series resistor and you putting a pull down resistor you are creating a voltage divider. If you have a 1K series resistor (R2) with a 330ohm pull down you will be reducing the voltage on that line by about 75%.

Vout = Vin * (R2/(R1+R2)) Where R1 is the series resistor and R2 is the pulldown.
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Old Apr 03, 2010, 12:40 PM
iPhly R/C with iPhone
iter's Avatar
Silicon Valley, Calif
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Quote:
Originally Posted by sotog View Post
I really don't know what is generating the PPM signal you are pulling down.
PPM comes from the headphone (audio out) line of an iPhone.

R2 in the module is 200 Ohm, nowhere near 1K.

Ari.
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Old Apr 03, 2010, 04:06 PM
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Oh Ok. I was going off of Jakesteramas schematic which showed a 1K.

I recently hacked a DM8 module and installed it into my Futaba 7CAP with a switch, but that was a bit more straight foward and I didn't need to mess with the PPM levels coming from the transmitter. I did remove the RF board connector and solder it flat to the PCB, that saved a bunch of space. I also changed the LED resistor to correctly bias it for a 3mm blue LED.

I did not put a scope on the PPM signal of the Futaba, so I am not exactly sure what input voltage range the DM8 module is expecting for that signal. But if you had that bit of info, you sould be able to divide down the voltage (if it is to high) and bring it to the level it wants.

Sounds like this is what you are experimenting with though.

Haven't had any experience with that particular controller, but have a decent knowlege in electronics if I can be of any help.
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Old Apr 03, 2010, 04:07 PM
Never enough RC time.
jakesterama's Avatar
Joined Aug 2007
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Quote:
Originally Posted by iter View Post
PPM comes from the headphone (audio out) line of an iPhone.

R2 in the module is 200 Ohm, nowhere near 1K.

Ari.
You might have a different version of the module than I do; mine is a 1k. I did some research and have found a few modules with a 201 resistor, so it is entirely possible.

http://en.wikipedia.org/wiki/Resistor#SMD_resistors

If you look at my schematic, R2 is a pull-up resistor, ie, it keeps the PPM line high (3.3V from the regulator) to the micro input if the PPM line from the TX is disconnected.

The thing I still don't get, is the micro only has a Vdd + 0.5V maximum input voltage (3.8V) and the module is designed to just pass the PPM signal straight from the TX to the module. Do the Futaba modules that this is designed for have a lower PPM voltage? I am not super familiar with the "programmable system on a chip" systems, so I am not sure if there is some way to program the "Direct switched capacitor block" to attenuate the input.
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Old Apr 03, 2010, 10:25 PM
iPhly R/C with iPhone
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Thank you for pointing out my error. I hadn't looked inside my own module, I was going on what I saw in this post http://www.rcgroups.com/forums/showt...=2#post7788582 and that appeared to me as "201". Now that I open my module, the writing on R2 is too small for me to read anyway! If I hold it one way, I see 201; if I turn it around, I see 102. But I measure 1K across it exactly as in your photo, so it must be 102.

I gather that old Futaba radios use 2.5V PPM signals. Not sure what you're saying about the 3.8V on the micro.

My audio line can generate up to 1.2V. This is enough to register in the micro, but with the pullup, the line swings from 1.9V to 3.1V instead of 0 to 1.2V and the micro sees it as all 1s. With my 330 Ohm pulldown, The line swings from 1.0V to 2.2 and the module recognizes that as a valid pulse train.

Ari.
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Old Apr 21, 2010, 02:58 AM
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Auxerre, France
Joined Dec 2007
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Hi guys,
Thanks a lot for that thread i read it with plenty of interest...
I love my Aurora... but i also love my P51 from ParkZone... and i know for sure i will love my 4sight from eFlight !
Trouble is that they all have DSM2 rx's... and it would be nice to use all the good stuff packed in my Aurora...
I wrote to Deborah @ Spektrum and got the usual response : no compatible module nor development !
Just a stupid thought (as i dont have your level of knowledge) : how about using other modules from spektrum ? it doesn't matter if the module case doesnt fit (we can check that point later). As they have developped modules for Mpx, JR and Futaba... any of these close enough to Aurora specs ?
Thanks for reading,
Ben
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Old Apr 22, 2010, 09:32 PM
Never enough RC time.
jakesterama's Avatar
Joined Aug 2007
72 Posts
Quote:
Originally Posted by ben999 View Post
Hi guys,
Just a stupid thought (as i dont have your level of knowledge) : how about using other modules from spektrum ? it doesn't matter if the module case doesnt fit (we can check that point later). As they have developped modules for Mpx, JR and Futaba... any of these close enough to Aurora specs ?
Thanks for reading,
Ben
That is exactly what this thread is about, using a DM8 originally intended for Futaba and Hitec radios in the Aurora9. Unfortunately the levels of the PMM signal are tricky to match correctly.

In the end I have found the swapping modules is a pain in the a$$, so I have sold my module and just going to hold on to my DX6i.
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Old Apr 23, 2010, 12:23 AM
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Joined Dec 2007
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Sorry to read that...
What i meant in my previous message is : there are other Spektrum modules available (for JRPropo or Multiplex or new shape Futaba) that might be "more" compatible than that one you have been testing... Any suggestion on which one would be best choice? I might have a go myself...
Thanks for your help.
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Old Apr 24, 2010, 01:02 AM
Never enough RC time.
jakesterama's Avatar
Joined Aug 2007
72 Posts
Quote:
Originally Posted by ben999 View Post
Sorry to read that...
What i meant in my previous message is : there are other Spektrum modules available (for JRPropo or Multiplex or new shape Futaba) that might be "more" compatible than that one you have been testing... Any suggestion on which one would be best choice? I might have a go myself...
Thanks for your help.
Hey, sorry I misread. That might be a good point, because the A9 is capable of switching between positive and negative shift, so using a different module might work...
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