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Old Aug 12, 2009, 02:26 PM
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Conversion of Hobbyking JR 2.4GHz TX-module to Futaba?

As many may know, Hobbyking has a JR 2.4GHz TX-module for $13.00, and 6/8 ch. receivers for $14.00! See: http://www.hobbyking.com/hobbycity/s...9ch_JR_Module_

There are a few somewhat vague threads about converting this module for use on JR radios, but there does not seem to be any specific conversion threads for Futaba.


It seems to be a relatively simple task of reducing the PPM and supply voltage from the Futaba module connector and hack the module in place!


Anybody had any luck yet?


(with the size of the potential market, I assume that Hobbyking will have a Futaba module soon, but this is for those who are impatient! )
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Old Aug 13, 2009, 07:31 AM
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I can currently working to make it work, It will take splitting the input bord from the RF board from the Jr module as it is too big to fit in the Futaba module as it comes, but from all I've read it should work. My one question is does anyone know what the voltage level of the PPM signal into the Futaba RF module is? I don't have a scope and would really not want to just guess. I have read at a couple sites that it MAY be around 3 volts, if so this would be great and no level adjustment would be needed.
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Old Aug 13, 2009, 11:18 AM
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There are lots of info about using Flysky's (HK manufacturer) RF board in other systems at the Flysky's 4&6 channles systems thread.

Its a very long thread, but Leadwing compiled a hack guide with the info.

The PPM signal should be 3,3 volts (voltage feeding the MCU at the input), but it seem to be tolerant, at least, up to 5 volt.
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Old Aug 13, 2009, 11:56 AM
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I'm looking for info specifically to the Hobbyking 2.4GHz JR -module- not the complete radio they sell.

I'm not sure if the module uses the same design as the RF portion of the Hobbyking 2.4 GHz radio, so other than basics like supply voltage and PPM voltage, any observations about the radio are somewhat moot here.


FYI, the only significant reason for interest in the module is that the shipping cost is a small fraction of the cost to ship the complete radio! (of which you'd toss most of it!)

Edit: I just ordered the JR 2.4GHz module and three 8-channel receivers and a few other components with a $5.95 shipping cost, versus $19.95 for the radio set, which has only 11g spare to the 999g limit.

If they had 6-channel receivers in stock, you could get four of them and the module and still be under the 250g limit for $5.95 shipping.

Also, a small box is far less likely to attract the attention of the Customs folks when it comes through!




Thanks.


Quote:
Originally Posted by MoFl
There are lots of info about using Flysky's (HK manufacturer) RF board in other systems at the Flysky's 4&6 channles systems thread.

Its a very long thread, but Leadwing compiled a hack guide with the info.

The PPM signal should be 3,3 volts (voltage feeding the MCU at the input), but it seem to be tolerant, at least, up to 5 volt.
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Old Aug 13, 2009, 12:23 PM
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Found some useful info in this thread: http://www.rcgroups.com/forums/showt...=387442&page=3


- "The photo indicates 2.15v - am I correct in my understanding that the PPM signal varies between 0 and +2.15v?"

- "tieing pin 3 to ground through a 100 ohm resistor seems to be fine for the Futaba radios"

The second point relates to the "RF Good" line.



Hope this helps!



Quote:
Originally Posted by Klondar
I can currently working to make it work, It will take splitting the input bord from the RF board from the Jr module as it is too big to fit in the Futaba module as it comes, but from all I've read it should work. My one question is does anyone know what the voltage level of the PPM signal into the Futaba RF module is? I don't have a scope and would really not want to just guess. I have read at a couple sites that it MAY be around 3 volts, if so this would be great and no level adjustment would be needed.
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Old Aug 13, 2009, 02:44 PM
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The RF section of the module is exactly the same as the RF board in the complete radio. There is a secondary board in the module that contains a voltage regulator and a range test button of sime kind. Yes it would require splitting the two boards to fit into the futaba module.
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Old Aug 13, 2009, 03:01 PM
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Quote:
Originally Posted by blanchjd
...Yes it would require splitting the two boards to fit into the futaba module.
Which probably explains why there is no Futaba module yet!

Regardless, so far it sounds like the Futaba implementation may be even easier than the JR hack! (due to the PPM signal being the right level in stock form...)


Can't wait to hear if it works! (and how to do it...)
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Old Aug 13, 2009, 03:07 PM
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Quote:
Originally Posted by meteor
I'm looking for info specifically to the Hobbyking 2.4GHz JR -module- not the complete radio they sell....
I forgot to say in my previous post that the RF section is the same in both cases, as blanchjd already said.

I'm attaching a photo of my 6 channel's RF section, and a photo posted by baxter at another thread of the inside of the HK module. As you can see, the RF board is the same.
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Old Aug 13, 2009, 03:16 PM
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Cool!


The boards are the same, but why does the "idiots guide" suggest you need a 5V regulator curcuit, when the daughterboard seems to have one on it?

After checking again, it seems that no-one uses the daughterboard, they just cobble together a separate 5V regulator and bind switch. Is there any benefit to doing this, other than a slightly smaller footprint?

Correcting myself here, but I think I get it now... The transmitter does not have a convenient regulator curcuit like the module, so this was never an issue/opportunity. Logcally, putting aside physical fit, this makes it even easier, right?


Hmmm...

(we still need to see if the Futaba PPM level, and the "RF Good" hack are OK for actual use...)
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Old Aug 19, 2009, 07:21 PM
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Quote:
Originally Posted by meteor
After checking again, it seems that no-one uses the daughterboard, they just cobble together a separate 5V regulator and bind switch. Is there any benefit to doing this, other than a slightly smaller footprint?
I just got mine today and had a good look, the soldering is atrocious, I would suggest the regulator/switch board be re-soldered.
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Old Aug 19, 2009, 07:25 PM
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I am also considering this, better yet I have two really old six channel radios that would be good for this as well. (and they would have more coolness)

One other thought off the top of my head, can the two receivers, main and satellite, be used separately? I still have some old AM car radios, JR and Hitec.
(yes I understand the satellite RX would need a PPM decoder for the servos, but easy to build)

RX and satellite RX are exactly the same, attached to one decoder board.
Looks like a voltage regulator on the board as well
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Old Aug 21, 2009, 05:07 AM
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Quote:
Originally Posted by ergocentric
...One other thought off the top of my head, can the two receivers, main and satellite, be used separately? I still have some old AM car radios, JR and Hitec.
(yes I understand the satellite RX would need a PPM decoder for the servos, but easy to build)...
The communications between satellite and main receiver is been investigated at the main thread for this system. Last posts about the subject were at page 110.

There you also have the schematics for ther 6 ch receiver.

Given the price of these receivers (possibly, cheaper than a DIY PPM decoder), I think the main interest for this investigation could be adding new features, for example, failsafe.

It's a pity the RX mainboard's MCU is custom made for flysky and undocumented, because the best alternative would be to develop a new firmmware for it...
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Old Aug 21, 2009, 11:50 PM
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So the receiver output is a serial data stream, not PPM?

Has someone scoped it? Do I need to dig out my osciliscope?

Thanks for the schematics.
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Old Aug 22, 2009, 01:58 PM
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Yes, the output from the satellite to the main receiver, and from daughterboard to maiboard inside main receiver, are serial data.

Apparently, spektrum does something similar but, dislike spektrum, Flysky's serial data is not readable with a PC serial port and realterm, because data blocks are 16 bit long (standard serial port is up to 8), and also non standard baud rate.

As vinc29 posted in the thread I linked before, there's a stream of 8 * 16 bits where each 16 bits is the duration, in us, of the PPM pulses.

Also, during power up, there's also serial data from the main board to the satellite, suposedly to preset frequency and GUID.

On the mentioned thread, you can find scope images (e.g, page 95), and an interpretation of the contents (that I summarized here).

BTW, vinc29 also thought of using the satellite an add functionalities, and is working on the subject, according to what he posted here.
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Old Aug 23, 2009, 04:10 PM
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Well, I finished transplanting the JR module guts over to a Futaba module case. I've attached a few pics on the installation. Not the prettiest, but it actually works. I didn't do anything with the the "RF Good" pin on the futaba module, but connected a wire in place in case I modified it further in the future.

A few bits of information about this install. It was intended to be a semi-permanent installation into a Team Associated XP3D 3-channel surface radio that I picked up real cheap. It has a futaba compatible module recepticle. I didn't measure the peak PPM voltage off it, as I didn't have the any caps to wire up at the time. It did however measure 0.5V on the meter. I figured the peaks were probably under 5V so I didn't worry about it much and I didn't add a voltage divider.

Here is the weird part though. The module worked fine on the XP3D, but not on my Futaba 3PJS. It measured 0.95V on the PPM line, so there is definitely a difference in the PPM voltage. I'd have to get the exact peak voltage to figure out if that was the problem.

Anyway, the boards fit just fine into the Futaba module case once they were separated. Overall, I'm pretty pleased.

-Jeff
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