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Jul 07, 2006, 06:23 PM
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Mr.RC-CAM's Avatar
Discussion

PPM Translator Processor for Spektrum DX6 (Unigen) RF Deck.


In the Radio Forum there is an interesting discussion that involves installing the Spektrum DX6 RF Module into a JR 6102 Tx. For full details please visit the sticky: Spektrumizing a JR6102 with DX6 Radio .

Some background: The Spektrum DX-6 RF deck utilizes a FCC certified radio modem made by Unigen Corp. This little RF module is fully FCC certified, on its own, and only requires a minimal amount of additional spectral testing (conformance validation) to meet the FCC requirements for use in ANY wireless product. Details are in the Unigen data sheet: JUNO-LPA Info. The FCC impact has been hashed to death in the other discussion, so please read it rather than post the same comments here.

The project discussed here is a small 8-pin microcontroller that can be used to incorporate the Spektrum RF deck with nearly any R/C Tx that has six or more channels. The integration requires someone with better than average electronic skills. So, keep that in mind.

The microcontroller is a Microchip PIC12F683 IC. It requires software, which is provided as a license-free-for-hobby-use download. The PIC accepts any Logic Level PPM encoded modulation, automatically inverts the PPM signal if needed, then outputs it as a negative going logic PPM signal that the DX-6 RF deck requires. It also truncates all servo data past the Ch-6 position, per the DX-6 reset gap requirements. Consider it sort of a universal PPM translator that "speaks DX-6."

The following posts will highlight the basic details. The rest is up to the technically competent user and their Tx's requirements. Please keep in mind that this project is not suitable to a beginner electronic tech. More importantly, the Part 95 FCC registration for the original R/C Tx will become invalid and the Unigen FCC registration ID will only be valid if the user performs the Part 15 spectral tests per the Unigen data sheet.
Last edited by Mr.RC-CAM; Jul 10, 2006 at 05:00 PM. Reason: Have validated PIC firmware. Done!
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Jul 07, 2006, 06:37 PM
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Mr.RC-CAM's Avatar
The basic schematic is below.

(1) The PIC requires 3.0VDC to 5.0VDC. If you cannot easily steal the 5VDC from the host Tx, then just use a common LM7805 VReg IC. Be sure to include the stability caps, as proposed by the Vreg's data sheet. You can also use the DX6's local 3.3VReg to power the PIC (change the D1 zener to a 3.3V type if you do).

(2) The PPM modulation input (J1-4) is provided by the host R/C Tx. If it is an open collector TTL level, then the Zener protection clamp diode can be omitted. Starting with V1.2, this input includes an internal pull-up resistor, which eliminates the need for an external pull-up in those apps that need it.

(3) The PPM output connects directly to the DX-6 RF deck PPM input.

(4) The LED is for status only and can be omitted. During use, if a repeating 3-blink sequence is seen, then the PIC is not detecting PPM on its input. If it blinks constantly, then it is properly locked on the Tx's PPM signal and all is well.

(5) PIC Pin-7 is for non-DX6 applications. It is a "positive logic" PPM output.

(6) PIC Pin-5 is a special output. Starting with V1.4, it is used with some Futaba Tx's to help sync the DX6 during boot. Please see post #162 for full details.

.
Last edited by Mr.RC-CAM; Sep 22, 2006 at 04:05 PM. Reason: Pin 5 has changed usage.
Jul 07, 2006, 06:50 PM
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The Hex file for the PIC12F683 is attached here. It is license-free-for-hobby-users only. It cannot be resold in any form (including pre-programmed PIC's).

The PIC fuses are as follows:
WDT: ENABLE
MCLR: DISABLE
CODE PROT: DISABLE
BODEN0 = 1
BODEN1 = 1
FCM = DISABLE
PWR TIMER: ENABLE
EE MEM PROT: DISABLE
IESO= DISABLE
OSC: INTRC OSC I/O
Last edited by Mr.RC-CAM; Sep 22, 2006 at 12:58 PM. Reason: Revised Hex File, V1.4
Jul 07, 2006, 08:36 PM
Model eAviator
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Jul 08, 2006, 12:31 AM
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Mr.RC-CAM's Avatar
The high end JR radios use a plug-in RF module. When it is removed, the five pin connector is exposed. This connector can be interfaced to obtain power and the PPM modulated signal.

(1) The photo below shows the connector.
(2) The schematic drawing shows a simple way to derive crude 5VDC power from the Transmitter's 6VDC regulated supply.
(3) The native JR XP8103 PPM signal is seen here. It is 8-Ch, positive logic.
(4) The last photo shows a scope display of what the processed PPM looks like (notice it reflects a 6-Ch PPM signal, even though the XP783 and XP8103 send 8-Ch data).

The PPM translator has been tested with both a JR XP783 and a XP8103 using the method shown in dwg 2. In both cases the translated PPM signal looks just like the encoded signal to the stock DX-6 transmitter.

.
Last edited by Mr.RC-CAM; Aug 14, 2006 at 08:40 PM.
Jul 08, 2006, 01:11 AM
Registered User
LukeZ's Avatar
Stupendifying! I just ordered a JR 9303 - now if I can only scrounge up enough pennies for a DX6, after the beating it gave to my wallet!


Luke
Jul 08, 2006, 01:28 AM
Buyin', Tryin' and Flyin'
hilgert's Avatar
The XP6102DX mod is nice in that it is self-contained, but this is actually "THE" solution, as it enables one to use the Spektrum as a "module" on a wider range of TX's. The JR XP9303 or an EVO 9 are my next targets for this.

-Hilgert-
Jul 08, 2006, 02:24 AM
It should fly at least once
clive45's Avatar

??


If only the DX6 module could be fitted into the JR plugin module.
Jul 08, 2006, 08:23 AM
Private Pilot/K5MBV/SCUBA
Nicetie's Avatar
Mr.RC-CAM

Is there any reason to use +5V instead of the +6V regulated for the circuit? I believe
most IC's are rated for 7V max so 6V is well within operating range. The logic levels
shouldn't change with supply voltage.

Ken K5MBV
Jul 08, 2006, 10:57 AM
Registered User
Mr.RC-CAM's Avatar
Quote:
Is there any reason to use +5V instead of the +6V regulated for the circuit?
The PIC should not be operated above 5.5VDC. In most cases there will be 5.0VDC regulated inside the Tx. The circuit requires <15mA to operate (less than 2mA if the LED is omitted).

In the case of the JR RF Module port, you can either use a LM7805 on the BAT+ pin, or use the JR port's +6VDC pin and do the crude two diode V-drop trick shown in the example circuit. The supplied voltage should fall between 4.7VDC to 5.2VDC.

Also, please note the D1 zener signal clamp on the PIC's PPM input. In the case of the JR series of Tx's, some have very large PPM signal amplitudes that would damage the PIC chip. For example, my XP783 sends PPM that exceeds 9V, but the XP8103 is standard 5V TTL logic. I suspect other Tx brands have similar situations. The Zener is needed to keep the input signal range under 5V. It is best to use an o-scope to see what the host Tx is providing, but if that is not possible then just include the Zener as a safety precaution.

FWIW, the circuit is Muntzed to its minimal parts count to keep it simple. If I was building a commercialized version (not going to happen) then it would be a bit more complicated. I think what is shown here should get the job done, but please feel free to expand the circuit to suit your needs.
Jul 08, 2006, 11:38 AM
Private Pilot/K5MBV/SCUBA
Nicetie's Avatar
"The PIC should not be operated above 5.5VDC."

I should have looked at the data sheet. ....my bad

Ken K5MBV
Jul 08, 2006, 02:56 PM
Registered User
Mr.RC-CAM's Avatar
Quote:
If only the DX6 module could be fitted into the JR plugin module.
Too bad that spare cases to the NET-J72P module are not available. With that, and some imagination, I think a nice looking plug-in solution could be devised for JR Tx's.

BTW, as a community effort, I'm hoping that the project details presented here will be utilized by a fellow that has access to a commercial RF lab. With the right talent (i.e., knows what he is doing, will work for free), we could resolve the FCC conformance validation issues. Please include a JR XP8103 in your tests.
Jul 08, 2006, 03:12 PM
That tree again!!!!
thanhTran's Avatar
Wow, cool idea! This should make DX6 works with 8-9-channel radios out there
Jul 08, 2006, 03:53 PM
Buyin', Tryin' and Flyin'
hilgert's Avatar
Quote:
Originally Posted by Mr.RC-CAM
BTW, as a community effort, I'm hoping that the project details presented here will be utilized by a fellow that has access to a commercial RF lab. With the right talent (i.e., knows what he is doing, will work for free), we could resolve the FCC conformance validation issues. Please include a JR XP8103 in your tests.
Part 15.23 allows one to do untested modifications to Part 15 equipment (and we are not really modifying the RF deck here) on up to five units for personal use. As long as one does not sell his work for gain I don't believe one has to go through certification (for personal use).

When my XP6102DX was tested at an FCC-licensed testing facility it was not really necessary other than to get the curmudgeons at the AMA moving to acknowledge (after working with the FCC) that the mod was not illegal. Whether you take the PPM signal from a 6102 or a 9303 (or whatever), it's still a PPM signal from the host TX, no different than the orginal mod on the 6102.

IMHO
Jul 08, 2006, 03:55 PM
Buyin', Tryin' and Flyin'
hilgert's Avatar
Mr.RC-CAM, take a look at your PM - I have another idea.


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