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Mar 03, 2007, 02:40 PM
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Discussion

OPEN SOURCE 2.4GHz (or perhaps 900MHz) SS SYSTEM


Any volunteers to embark on the above named project? I have done some preliminary research and believe that it is doable. Some assumptions:

TX MODULE:

In order to appeal to the widest audience, the TX portion will utilize the trainer port instead of being a plug-in module. For the RF link, off-the-shelf components from Unigen or Maxstream. Due to easy availability (several sources including Digikey etc.) the best choice would be the Maxstream XBee Pro ($32 each in single quantities). I have used chip level RF components (in other projects) that give much higher data rates (2-4Mbits/sec) but would not be feasible here due to the need to obtain FCC approval for their use - therefore the recommendation to go with Maxstream. The TX component will be clip-on type configuration. A 128x64 graphic LCD will be incorporated to display status and optional telemetry data. Size of the TX component is 3.5x2.75x0.75in. Also, the case for the TX component will preferably be another off-the-shelf part.

RX MODULE:

The RX component can be a clear shrink-wrapped configuration thus obviating the need for a case. Side exit pins for connections are recommended.

I have done the background research for MCU’s and would be willing to do the coding for the main portion of the system - capture PPM, send to RF, receive RF, decode back PPM etc. Additional features such as 2-way comms for telemetry and other features, would require volunteers.
Last edited by rmteo; Mar 20, 2007 at 07:42 PM. Reason: added description to pic.
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Mar 03, 2007, 03:17 PM
And You're Not
That was quick!

Quote:
Originally Posted by ncrego
I swear, sometime in the next year or so, I'm going to make a false user name on all the forums and do exactly the same thing and see if I can draw in as many people as he can.
Seriously though, I've been looking at the RX decoder circuits. The TX encoding is already done unless I'm mistaken, looks the RX is going to be the most work.
Mar 03, 2007, 03:46 PM
Registered User
Sounds interesting. I would consider volunteering, but I have non of the needed skills. My questions would be:

Who are you? You don't even have a location in your description.
Are you just after volunteers and/or a discussion?
How about a quick write up for the masses, on how your system components works? A tutorial of a basic diy ss system, if you will. What encoding? We are all familar with ppm, but not the new digital stuff.

I would be interested in some user programmability via pc inteface. Any thoughts on how this can be useful?

I think this thread should be in the DIY forum. You will have many more comments there and meet people who able to help with development.

-Kwok
Mar 03, 2007, 05:10 PM
User
Thread OP
At this stage, I would like to see if there is sufficient interest. If there are enough of people interested in participating, the first thing to do is to develop basic specs for the system. We can then go into details.

Here is a mechanical layout for a 12 channel RX showing the XBee Pro. Size is approx. 1.35x2.25x.0.50in.
Mar 03, 2007, 07:03 PM
Registered User
I have a question-------WHY?

There is no way you are going to save any money over complete systems now on the market. Neither is there much chance that you are going to make a "breakthrough" in any form of the design areas required.

I came into this hobby when you built from schematics-------I have less than zero interest in going back to it.

FCC approvals are not the least of your problems. Insurance will be. Today they award absurd verdicts for liability issues--------where are you going to fly---certainly NOT at any of the clubs I belong to.

If you like to ponder hypothetical solutions ----ponder away-----I just feel that there are more interesting areas in which to ponder.

TIC Take the wheel for instance-----hasn't been a 'revolutionary' change in quite some time-----and way more users to be considered for input.
Mar 03, 2007, 07:09 PM
And You're Not
I think you can build your own system without any FCC approval under Part 15, just can't sell them.
Mar 03, 2007, 07:20 PM
User
Thread OP
Thanks for pointing that out, Jeffery. Here is a quote from FCC15.249:

Hobbyists, inventors and other parties that design and build Part 15 transmitters with
no intention of ever marketing them may construct and operate up to five such
transmitters for their own personal use without having to obtain FCC equipment
authorization. If possible, these transmitters should be tested for compliance with the
Commission's rules. If such testing is not practicable, their designers and builders are
required to employ good engineering practices in order to ensure compliance with the
Part 15 standards.


Added: The above may not be applicable if off-the-shelf modules are used (you can market the product). This from the Maxstream data sheet:
FCC Approval (USA) Refer to Appendix A [p57] for FCC Requirements.
Systems that contain XBee/XBee-PRO RF Modules inherit MaxStream Certifications.

There are some labelling requirements that need to be adhered to.
Last edited by rmteo; Mar 03, 2007 at 07:37 PM. Reason: added comments.
Mar 03, 2007, 07:41 PM
Registered User
Is the power limit 1 Watt for Part 15 for 900 MHz and 2.4 GHz?

I'd like to see some homebrew designs for spread-spectrum so I might get greater range at lower frequencies. For example, the 2 meter and 70 cm ham bands are not only interesting for greater range for RC (1 Watt goes further at lower frequencies) but also provide extreme range for video where there is no power limit (actually 1.5KW) from your plane to ground.

I for one, am extremely concerned about being 'shot down' using the 72 MHz band since about every RC toy is now using that band. I strongly believe that the AMA should not allow 72 MHz RC at sanctioned fields because of serious safety issues. Spread-spectrum should be mandated by AMA!
Mar 03, 2007, 07:47 PM
Inciting Riots
village_idiot's Avatar
You might want to check on the output levels for part 15 2.4 Ghz transmitters, it may be significantly less than licensed/certified devices. I know that the 900Mhz devices have a fairly high level allowed, somewhere in the 50,000 uV/meter at 3 meters range, you can get a pretty good range from that much signal.
Mar 03, 2007, 07:52 PM
User
Thread OP
This is what I found:

(b) The maximum peak conducted output power of the intentional radiator shall not exceed the
following:
(1) For frequency hopping systems operating in the 2400-2483.5 MHz band employing
at least 75 non-overlapping hopping channels, and all frequency hopping systems in the 5725-5850 MHz
band: 1 watt. For all other frequency hopping systems in the 2400-2483.5 MHz band: 0.125 watts.
(2) For frequency hopping systems operating in the 902-928 MHz band: 1 watt for
systems employing at least 50 hopping channels; and, 0.25 watts for systems employing less than 50
hopping channels, but at least 25 hopping channels, as permitted under paragraph (a)(1)(i) of this section.
(3) For systems using digital modulation in the 902-928 MHz, 2400-2483.5 MHz, and
5725-5850 MHz bands: 1 Watt. As an alternative to a peak power measurement, compliance with the
one Watt limit can be based on a measurement of the maximum conducted output power. Maximum
Conducted Output Power is defined as the total transmit power delivered to all antennas and antenna
elements averaged across all symbols in the signaling alphabet when the transmitter is operating at its
maximum power control level. Power must be summed across all antennas and antenna elements. The
average must not include any time intervals during which the transmitter is off or is transmitting at a
reduced power level. If multiple modes of operation are possible (e.g., alternative modulation methods),
the maximum conducted output power is the highest total transmit power occurring in any mode.
Mar 03, 2007, 07:55 PM
Registered User
{Quote}
I strongly believe that the AMA should not allow 72 MHz RC at sanctioned fields because of serious safety issues. Spread-spectrum should be mandated by AMA!
{Quote}

Now THAT should bring some interesting replies.

If you think 72MHz has a few problems you should try six meters in the spring time (Gen. Class for 30+ years). I flew totally without a bounce for over thirty years on six ---- then ZAP ---- 1500Watts one time. May 29, 2005 to be exact! My equipment was the best money will buy.

Stopped adding when I got to the first $1000!

Guess what I fly now??

Home brew-----not on your life!! BTDT

BTW it is more than Part 15---don't quote me but 18 ISM sticks in my mind---though I don't even have enough interest to look up the source.
(Try Part 18 -----47 CFR)\

SORRY gang but I think you are WAY out of your league!!! Color me GONE.
Last edited by onewasp; Mar 03, 2007 at 08:14 PM.
Mar 03, 2007, 08:04 PM
Guz
Guz
Gutless wonder
Guz's Avatar
I think this a GREAT idea!!

1. The Tx and Rx RF deck would be allowed with the FCC, as said before, the chipset manufacturer has the FCC ID. We just ride on their coat tails.

2. An open source transmitter would be awesome! Programming that makes sense. No more dealing with what is handed by someone else (Asian or European).

If the transmitter itself was designed properly, by using RF modules we wouldn't be limited to just 2.4 gHz, we could go on to 900 mHz, or even back to the current frequencies.

I've got very limited abilities to contribute, but would do my best.

<edit>
Oops. You're just talking about RF modules, not the transmitter. That's still good!
Mar 03, 2007, 08:22 PM
And You're Not
Quote:
Originally Posted by onewasp
SORRY gang but I think you are WAY out of your league!!! Color me GONE.
There are some pretty talented individuals on this board, many have a lot of experience in fields other than RC airplanes. I'd never discount an idea as being out of the league of the combined expertise of the posters on this website.
Mar 03, 2007, 09:12 PM
Send Money, Women & Guns!
fritzthecat's Avatar
So you want to copy the XPS system which uses the same XBee Pro modules?

Fritz
Mar 03, 2007, 10:21 PM
Registered User
kilwein's Avatar
I can buy quan 1 cost a FHSS tx-rx module for under $99 and with two I have a complete system that is certified to FCC already. They are small enough to fit 3 inside a tx case. 100mw and 114 dB sensitivity. Numbers sound familiar?
With some coding they work fine in our application and you have true two way links.
With a $40 display and some glue logic you have telemetry.
I have my FCC commercial license and design hardware that runs at over 4GHz currently. I let my ham license expire a long time ago. With this I still will not bother to make my own SS module for my stuff. I will however tune what I have to be on freq.
I bought a new 14mz a short time ago and I was surprized it was only off freq by 18 cycles. This was measured with equipment certified up to 12GHz.

If you want to pursue do a search on 2.4g tx-rx mudules, there are many out there already and you can even pick the 900MHz band for same prices. The companies will
do the programming for you but you will pay for their services. Some are very flexible in what they can do. I have seen some that are one way for less than $60 each but
they are basic modules with limited purposes. They are also in different power versions.

Good luck on your pursuits.


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