Replies to This Discussion

Permalink Reply by Allen Babb on September 2, 2011 at 3:45pm

Well, if your in the U.S. or its territories, you'll have to comply with FCC rules... which boils down to a very limited range and can only do AM transmissions. FCC: Title 47

 

There's one or two parts that should apply specifically to your application. If you have a Tx and Rx already, there should be a FCC sticker that says something to the effect of "Complies with section blah blah of part blah blah of Title 47," look for the section and part that's in, and see what you'll be able to do without a license. If that's not enough, well, I guess you'll have to get a license.

 

You might actually be better off going with the existing technologies first, such as the Xbee's, so as you can get a feel for wireless communications and its quirks.

 

There's quite a bit on Communications Engineering, which is a subfield of EEEN that looks specifically at the electrical and electronic exchange of data (wired and wireless). It's pretty heavy in Random Signals theory and Laplace domain equations, and is not suggested for those without at least an understanding of Linear Algebra and Fourier and Laplace mathematics.

 

As far as your circuits goes, Try out Sparkfun.com for part supplies and some instruction on the construction of the electronics.

• ▶ Reply

Permalink Reply by Allen Babb on September 2, 2011 at 5:07pm

Title 47, Part 15

 

Subpart A, sections 5, 9, 15, 21, and 23 may be of particular interest to you.

 

Don't forget to check the other subparts further down on the page.

• ▶ Reply

Permalink Reply by Jake Stew on September 6, 2011 at 2:43pm

> you'll have to comply with FCC rules... which boils down to a very limited range and can only do AM transmissions.

 

Please elaborate on that...  What's to stop a 433mhz ISM band radio on a chip that puts out 100mw (1W is the limit IIRC).  AFAIK you can put out 1W on any of the ISM bands (433/900) if you're using FSK, GFSK, FHSS, OOK, etc..

 

They're making 900mhz radio modems putting out 1W on the ISM band and claiming they're US legal.  I think you may be thinking of other transmission methods (way larger bandwidths) or different frequency bands.

 

We're talking packet radio modem data here, not FM/AM modulated audio or video.  Those take larger bandwidths and transmit on the same channel with over several mhz width.  We're talking about data packets that transmit on an exact frequency and hop around to different frequencies frequently (every couple-several milliseconds).

• ▶ Reply

Permalink Reply by Allen Babb on September 6, 2011 at 3:58pm

My replies where under the assumption that the OP was going to try making his own transmitter and reciever radio from scratch, which I see now is not what what he was referring to when he said "Tx" and "Rx".

 

I haven't had many chances to understand the lingo of the R/C industry, probably hence my confusion.

 

At any rate, if a chip radio is available to the public, then I would hands down select it over trying to build a radio from scratch... although I hear it has its own rewarding experiances.

• ▶ Reply

Permalink Reply by Matt on September 6, 2011 at 9:03pm

That is correct Allen. I'm Finishing up a degree in Professional Aeronautics and starting on Electrical Engineering - so I want to get a head start by doing a mini project like this. This is strictly for educational purposes.

 

Thank you everyone, for all the input so far.

• ▶ Reply

AdminPermalink Reply by Thomas J Coyle III on September 3, 2011 at 7:57am

Matt,

You might want to take a look at this thread to get an idea of what it takes to build a custom TX/RX combo: http://www.lynxmotion.net/viewtopic.php?f=21&t=4399

I presently have several of the PCTx interfaces and am investigating interfacing the PCTx to a Spektrum DM8 rf module. I believe that the PCTx signal will have to be inverted to work with the DM8 rf module.

This undertaking will not be a trivial task. Good luck.

Regards,

TCIII

• ▶ Reply

Permalink Reply by Matt on September 6, 2011 at 9:09pm

Thanks for the link! BM'ed.

• ▶ Reply

Permalink Reply by Jake Stew on September 6, 2011 at 2:38pm

I have the same project planned.  Might have a little more electronics experience.

 

If you've checked out the OpenLRS project...

http://blog.flytron.com/category/openlrs-project

http://forum.flytron.com/viewforum.php?f=7

 

They're using a Hope RF module (RFM22B) and a microcontroller.  Specs are 100mW @ 433mhz, with 121dB recieve sensitivity IIRC.  The module uses an Silicon Labs radio on a chip.  The SiLabs chip has 256kbps data rate, 100mW output power, and an amazing 121dB recieve sensitivity.  The Hope RF module looks like a little SMT board with the chip and about 27 SMT resistors, caps, and whatnot.

 

Since OpenLRS uses a SMT motherboard that the module plugs into already I'm not sure why they're not putting all this on one board.  The module can only make it cost more.  Then again it's not that expensive (about $16 I think) and they're probably getting a good volume discount.

 

Anyways, I got the idea of using the new SiLabs 1000 (1001,1010, or 1011) SoC (system on a chip).  This chip uses the same radio but adds a uC to the mix.  Using a SoC radio we should be able to eliminate the separate microcontroller, reduce costs, complexity, and power requirements.  The SoC has the same radio specs.  Hope RF also makes a module based on this chip (RFM50), which looks like it uses about 35 SMT pieces.

 

My idea is this... Use the SoC radio chip and a TI TLC5940 16 channel PWM controller chip (serial interface to SoC chip) to make a nice controller/RX/TX board.  By offloading the PWM to the TLC5940 we should be able to get excellent PWM control for driving the servos without wasting GPIO pins or clock cycles.

 

I'm pretty confident we could make the simplest and cheapest RC TX/RX system to date.  It would have 100mW @ 433mhz, 256kbps data rate, and amazing -121 dB receive sensitivity.  At a bare minimum this should do 1.5 mile+ control and allow 2-way telemetry and commands.  This should be an ultra-cheap 2 chip SMT board with plenty of extra features to find a use for.  

 

The radio chip is just awesome! Very low external component count, super low current consumption, 100mW out of the chip, and unmatched receive sensitivity.

 

My hope is that once a prototype is built we'll find that there is enough computing power and pins left over that we can implement an entire autopilot and telemetry sensor package.  That would be the ultimate goal, and if it doesn't work out it shouldn't be that hard to add another uC to do the autopilot/sensors.

 

In any case it would be nice to build a RX/TX/autopilot/sensor board that can be done with 2-3 chips and a couple dozen SMT pieces.  It would be the most modern and cheapest design to date by far.  OpenLRS also has a 7W TX module (legal?) BTW, so all the work for an extremely long range system has already been done.  1W seems like a nice round number to me and is probably the most you can legally transmit on ISM bands in the US.

 

Anyways, all that has to be done is work off the Hope RF modules/OpenLRS schematics and code.  We just design a new board using the SoC instead of the 2-chip solution and port the code over.  Simple right? LOL

 

Well, that's my grand scheme for the next gen long range controller system.  I need people to help me.  On my own it will be completed in about 5 years.  But if anyone else wants to use the latest and best ICs to make the simplest, cheapest, best performing system with the most features of anything out there, then post here.

 

I'm hoping to get a couple Hope RF modules, a SiLabs devkit for the Si10XX, and engineering samples for almost everything else within the next two months.  Hopefully I/we can cobble together something for a ground test before X-mas.

 

 

 

 

 

 

 

 

• ▶ Reply

Permalink Reply by Matt on September 6, 2011 at 10:06pm

I'm 100% interested. I sent you a PM with my email address.

• ▶ Reply

Permalink Reply by Jake Stew on March 2, 2013 at 7:25pm

Not sure if I ever got your PM.

I found d6labs.com as a great source for RFM50 modules and other odds and ends.  They sell the needed 30mhz crystals for $0.90, but I don't think they're up on the website yet, you'll have to email them directly.

I've got 6 of the modules, a couple pairs of antennas, a SiLabs programmer from ebay, and a few other odds and ends on the way.

I don't see to many problems ahead other than the sheer amount of time involved in designing the hardware and software.  But when it's finished it should be, by far, the best radio setup out there at a fraction of the cost.  Essentially, all the current radio modules out there will be obsolete, so it's a good time to ditch other legacy foolishness like using analog PPM signals. 

• ▶ Reply