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Jan 12, 2005, 05:11 PM
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Plantraco DSP4-SC Decoder Project, Cont'd.


There is a long thread on eZone that describes how some Plantraco DSP4-SC Rx users are suffering from serious glitches. This new discussion is a spinoff that describes new decoder firmware that I have been working on. It is sufficiently off-topic that I decided to start up a new discussion.

Here is the old thread: https://www.rcgroups.com/forums/showthread.php?t=280520

In that thread is a post that describes the weakness of the existing decoder that is used. Here is a direct link: https://www.rcgroups.com/forums/show...&postcount=129

The revised firmware has passed my bench tests. I am waiting for some decent weather and some free time to actually fly with it. In the meantime, I promised progress updates. I have nothing new to add, but I thought I would review the details.

Here are the features of the new "Digital Decoder Engine:"
  • High quality DSP decoder using faster PIC Microcontroller with extended hardware features.
  • Fully decodes all four channels, using a frame buffered post processing approach. Does not impact servo latency.
  • 1024 servo step size (10-bit) versus original 200 step (7.5-bit) resolution. Jitter is now under 1uSec!
  • Complex PPM signal signature analysis using historical R/C PPM data.
  • Bad PPM signals are allowed 1.5 Secs of flywheeling servo hold, then go idle. (Like Berg).
  • Auto-Shift detect with last-shift-used-memory (for lightning fast Tx signal lock). Now supports JR (positive) shift. Internal ESC moves to correct channel too!
  • ESC PWM rate increased to 3KHz rate (originally was 1.7KHz). This may offer higher motor efficiency. Internal ESC has over 512 step resolution.
  • One new PIC Microcontroller replaces the two existing PIC's.
  • Standard motor arming sequence (low stick, high stick, low stick).

The two photos below show the board changes. The parts are very small, so don't let the photos fool you. Magnifying lenses and patience are required to perform the micro-surgery.

The first photo shows the new PIC12F683 IC microcontroller. It drops into the old decoder's location. You will also see that the old ESC microcontroller is gone. A piece of wire goes in its place.

On the bottom side you can see a new 10K resistor that must be added. It is required by the new PIC microcontroller. Not shown is a second resistor that is needed if a JR (positive) shift transmitter is used. Details to my trying to avoid the resistor are chronicled here: https://www.rcgroups.com/forums/showthread.php?t=318386

It will be a few weeks before I will know if the new decoder's performance is up to my expectations. The project has been very time consuming and at this point I need to take a break from it.

RC-CAM
Last edited by Mr.RC-CAM; Jan 13, 2005 at 01:52 PM.
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Jan 13, 2005, 09:56 PM
BEC
BEC
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BEC's Avatar
Amazing stuff. I will be very interested to see if Plantraco will make good use of your hard (and obsessive!) work. The analysis of what's really going on that you link to above is VERY enlightening.
Jan 15, 2005, 08:18 AM
I USE CAPS - EYE TROUBLE
Happymcc's Avatar

Amazing at the very least


Yes I agree Amazing .
I only wish I had the knowledge to do something like this .
It does however give me some peace of ming to know why
my sons plane hit the ground so many times before we changed
out the receiver . I do understand enough to follow the explanation
of the DSP decoder and what was wrong and what was changed
in the new DSP build .
Again I say Thank You Mr.RC CAM

And for those of you that don't have the skill to modify a receiver
like this , I say to you Get A Berg
Jan 15, 2005, 10:45 AM
Crash Master
Gene Bond's Avatar
Thanks again for your hard work and dedication to explain the 'unexplained', Mr.RC-CAM.

It never ceases to amaze me that there are so many people who are as obsessive as I am about something that just isn't right. I just wish I had the tools (mental, physical, hardware) to attack some of the problems you have identified and resolved.

I was pointed to your report from the thread in indoor about fixing the GWS and Feather rx's by adding a PIC w/ DSP: https://www.rcgroups.com/forums/showthread.php?t=320480

It sounds as if a 'Universal DSP Adder' could be developed which may fit any inferior design out there. I look forward to the day we can possibly retrofit our old rx's with a simple fix. I actually thought an 8 i/o chip may be able to be retrofitted between the servo plugs and sockets, making a 'plug and play' option board. Would that be cool, or what?

I hope Plantraco and others take notice of your work and at least re-open the project, and clean up the code. Maybe the best thing would be for you to offer to licence your code to them?

Again, thanks for the efforts!
Jan 15, 2005, 01:47 PM
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Quote:
It sounds as if a 'Universal DSP Adder' could be developed which may fit any inferior design out there. I look forward to the day we can possibly retrofit our old rx's with a simple fix. I actually thought an 8 i/o chip may be able to be retrofitted between the servo plugs and sockets, making a 'plug and play' option board. Would that be cool, or what?
That was one of my project goals. A few weeks ago I picked up a couple of Feathers and GWS Picos to try my chip on. However, after reviewing their board layouts, I must say that hacking them to integrate the 8-pin microcontroller will be totally brutal. Probably outside the skills of 99.9% of the eZoners out there. Too bad.

It may be seem tempting to just design a DSP decoder gadget that plugs into the servo connectors (for hack free upgrades). But, the results would definitely not be as good as feeding the DSP hardware with the native demodulated RF signal. The plug-in solution would be heavier and bulkier too.

I am not sure where my project will eventually go, beyond my own personal use. However, this exercise did lead me to a valuable conclusion. That is, just because an R/C Rx maker claims unbelievable DSP Rx performance in their marketing literature, don't make it so. It makes me wonder how well some of the other high-tech Rx designs behave when subjected to practical, but worse case, field conditions. Not all of us fly in perfect environments and so sometimes it really matters when the design isn't sufficiently robust.

RC-CAM
Jan 16, 2005, 01:21 AM
Always right
Hovertime's Avatar
Will this be added to your project page with code etc?
Digital revolution, slow to come, but when it hits it hits...
Jan 16, 2005, 01:35 AM
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Quote:
Will this be added to your project page with code etc?
I don't think I will do that. But I may offer a programmed chip at a fair cost.

It would make a nice decoder for a home-brew 4-Ch Rx. And just think, if you add a cheap MOSFET to it you will get a brushed ESC for nearly nothing.

RC-CAM
Jan 19, 2005, 09:51 PM
Smooth landings!
Hi, everyone!

I just made a DSP4-SC upgrade announcement announcement at https://www.rcgroups.com/forums/show...87#post3193087

Enjoy!

MikroDon
Jan 27, 2005, 01:01 AM
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April-02-2005 Update. I have sent off a couple dozen of the DSP4 chips to eZoners. After some feedback is received I will determine if I should continue the project. Until then, the DSP4 chip offer is suspended. BTW, there is a lot of discussion about DSP decoders in general going on here: https://www.rcgroups.com/forums/showthread.php?t=298197

Original Post:

The decoder I created will work on just about any R/C Rx where three or four channels are needed. If anyone is interested in trying it out on their custom Rx project, then I have a win-win idea for you.

If you send me a PIC12F683 chip (max 2 pcs), and sufficient postage to return it (two First Class stamps), I will program the PIC for you at no charge and mail back to you. This will help me test it and you will get a glitch free decoder for your custom Rx project. If you do not want to send me a part, then I can supply them for $5 each for DIP-8 package and $6 each for SOIC-8 package (SOIC availability is limited, so order early if that is what you want). If interested, please PM me (do NOT use email).

The PIC12F683's pinout is as follows:
Pin 1: V+
Pin 2: CH3
Pin 3: CH4
Pin 4: PPM In
Pin 5: Optional 3Khz PWM for N-MOSFET based ESC
Pin 6: CH1
Pin 7: CH2
Pin 8: Gnd

This would be nice chip to try on a Hitec Feather or GWS Pico Rx. I'll leave the installation details up to you.

RC-CAM
Last edited by Mr.RC-CAM; Apr 03, 2005 at 01:41 AM. Reason: Now waiting for feedback. Offer suspended.
Jan 27, 2005, 01:19 AM
Always right
Hovertime's Avatar
Interesting, how does it compare to Bruce Abbot DSP add-on chip project? https://www.rcgroups.com/forums/showthread.php?t=298197

I am also waiting for some sample 12F683's ... I would try to upgrade GWS 4P Futaba shift receiver. Any extra parts needed?
Jan 27, 2005, 01:26 AM
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Quote:
... how does it compare to Bruce Abbot DSP add-on chip project?
I'll leave that up to you. Details to my version's behavoir is discussed in this thread. For the cost of a few stamps you can make the judgement for yourself.

RC-CAM
Feb 03, 2005, 05:56 PM
Pesky Landings!
bigandy's Avatar
Hi there Mr.RC-CAM,

I was just wondering if you would mind sending a couple of programmed PIC's across the atlantic to the UK? I'm looking at alternative decoders to go in a couple of hitec feather receivers here on 35Mhz, and your design and Bruces design look to be pretty good. One thing I am keen to get is a decent failsafe with minimum added airborne weight. I probably value that above the DSP gubbins and the esc to be honest! anyway, you've pretty much sold your version to me, wheras I still have doubts about bruce's design.

The other option I was going to ask you via PM, but I chsoe to ask here instead is if you would consider "licensing" the hex code for the PIC12F? I would be willing to pay a few beer tokens if it meant I could burn a chip to go in a receiver myself. I'm not really interested in the asm code, as to be honest, I can only just manage to burn a PIC using a hex file and build a basic circuit, never mind write Asm code!

Cheers
Andy
Feb 03, 2005, 06:04 PM
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Thread OP
Quote:
I was just wondering if you would mind sending a couple of programmed PIC's across the atlantic to the UK?
My offer is for any eZone or RC-CAM forum member, including those outside the USA. Just PM me.


Quote:
... would consider "licensing" the hex code for the PIC12F?
Not at this point.

RC-CAM
Feb 05, 2005, 07:46 PM
veni,vidi, roto volubilis
Happy|Harry's Avatar
RC-CAM how much for a programmed chip sent to the UK? i'll be trying it in a GWS R4N also do you take paypal?

phil
Feb 05, 2005, 09:54 PM
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Thread OP
The special offer discussed in post #9 is extended to any country that I can send a postal letter to. The price (if you do not use the free service) is as shown, regardless of country. PayPal is great. Please PM me to obtain my PayPal details.

RC-CAM


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