HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jan 05, 2013, 08:51 PM
Registered User
United States, ID
Joined Sep 2011
417 Posts
Quote:
Originally Posted by Helldesk View Post
From what I gathered from elsewhere, I got the impression that the 3DR implementation is a bit overengineered with a whole extra chip on them, when the Si1000 could possibly take care of everything alone. I guess it's the issue of non-exposed pins then that dictated that design choice?
The Si1000 is a 3.3v chip, and it doesn't have USB. The 3DR ground module has a serial to USB chip on it to communicate over USB. I've got a pair, so I'll look them over, but there's not much there except the HopeRF module.


> do you think a 10% duty cycle I listed earlier could possibly work for controlling a flying machine?

Sure. The link is already half-duplex, so you're already at 50% if you balance the up/down link bandwidth.

If you figure 128 or 256kbps then at 10% you still have 12.8 or 25.6 kbps. 12,800 bps is 800 16-bit values per sec.

You want a 50 Hz update rate, so 50 * number of channels * 16-bits. That's 6400 bps, or half of what you'd have at 10% * 128kbps.

That should be no problem, and there should be plenty of room for telemetry since that will be coming from the air side. 12.8kbps in each direction should be plenty.
jakestew is offline Find More Posts by jakestew
Reply With Quote
Sign up now
to remove ads between posts
Old Jan 07, 2013, 01:19 AM
Registered User
Columbus Ohio.
Joined Aug 2006
151 Posts
I believe if you buy a tranceiver that resides on a module board inclusive of the amplifier, antenna, etc....it's that piece the carries the FCC(USA) certification. By the same token, if your commercial radio (Fatuba, Spectrum, JR, etc.) takes a plugin RF module, it's the module that is certified.

The main box of the total radio talks to the RF module throught some sort of digital IO like SPI. The RF module contains all the "real Radio communications stuff"...RF Radio, amplifier, filters. antenna...yada yada. Now if everyting including the RF componest are housed in a single case...then it's the whole radio that is certified.

My Spectrum DX5 radio is all inclusive, and it has an FCC number. I wonder if that new Orange Radio from Hobby King is FCC certified?
RJKIRK is offline Find More Posts by RJKIRK
Last edited by RJKIRK; Jan 07, 2013 at 01:29 AM.
Reply With Quote
Old Jan 07, 2013, 01:24 AM
Registered User
Columbus Ohio.
Joined Aug 2006
151 Posts
PS...to operate 433 Mhz legally in the US you need a Technical Class Ham License. I got mine license for that specific purpose.

910 Mhz is open to everyone, as is 2.4Ghz.
RJKIRK is offline Find More Posts by RJKIRK
Reply With Quote
Old Jan 07, 2013, 03:47 AM
Registered User
United States, ID
Joined Sep 2011
417 Posts
> The main box of the total radio talks to the RF module throught some sort of digital IO like SPI.

The controller (what people like to call the "radio") talks to the TX module using analog PPM. Some seem to have options to use PCM, which is a digital method, but I haven't seen that used much.

> PS...to operate 433 Mhz legally in the US you need a Technical Class Ham License.

Ham users like to claim that, but 433 is part of the ISM band and you don't need a license.

FCC regs are such a mess and they're such a corrupt and worthless organization that it's pretty much impossible to figure anything out. There's sections that restrict and sections that permit, and they reference each other randomly to the point it looks like a bunch of insane retards wrote them.

I ordered a few SiLabs chip samples, but they're out of the lower pin count versions, so I'll have to see if I can actually etch and solder those tiny packages.
jakestew is offline Find More Posts by jakestew
Reply With Quote
Old Jan 07, 2013, 04:39 AM
Stuart
srnet's Avatar
UK, Cardiff
Joined Dec 2008
3,073 Posts
Quote:
Originally Posted by jakestew View Post
All the current mainstream TX/RX radio control units available today are overpriced, low-power, analog units transmitting on poor frequency bands.
Hardly the best justification for a project I have seen.

I have used a range of RC systems over the years, AM and FM and the newer 2.4Ghz systems. They are cheap and have perfectly adequate power and range for the vast majority of users. I can fly planes to the limit of my vision, 2000ft or so, with even very cheap RC systems.

Whilst you say that more TX power is needed, is that really true ?

The very big danger with building in more power is that the vast majority of users would just abuse it. Then you get a situation whereby you now need to use large amounts of power just to overcome the amount of interference from everybody else who is using high power.
srnet is offline Find More Posts by srnet
Reply With Quote
Old Jan 07, 2013, 04:45 AM
Stuart
srnet's Avatar
UK, Cardiff
Joined Dec 2008
3,073 Posts
On the topic of the Hope RF modules, I have done a fair bit of work on the RFM22, for a satellite project.

The legal limit for license free use of the 433Mhz band is 10mW in a lot of the World, so I presume that would be the limit to be designed in.

At 10mW, the RFM22 will give you about 12kM line of sight for low speed data telemetry, and maybe only a couple of hundread metres in an urban area.
srnet is offline Find More Posts by srnet
Reply With Quote
Old Jan 07, 2013, 06:07 AM
Registered User
Geoff_S's Avatar
Brisbane, Australia
Joined Feb 2002
765 Posts
Quote:
Originally Posted by jakestew View Post
The controller (what people like to call the "radio") talks to the TX module using analog PPM. Some seem to have options to use PCM, which is a digital method, but I haven't seen that used much.
Almost all of the major brands that are still offering modules in 2.4ghz have moved away from PPM (or PCM) communication between the modules and TX in lieu of some digital protocol (eg Multiplex with their Royal Evos have been doing it for years even on FM, Hitec with the Aurora, JR with the XP9303 and 12X, Futaba 10C etc etc)
Geoff_S is offline Find More Posts by Geoff_S
Reply With Quote
Old Jan 07, 2013, 07:36 AM
RC beginner
New York
Joined Oct 2008
5,622 Posts
[QUOTE=srnet;23737367]
Quote:
Originally Posted by srnet View Post
Hardly the best justification for a project I have seen.

I have used a range of RC systems over the years, AM and FM and the newer 2.4Ghz systems. They are cheap and have perfectly adequate power and range for the vast majority of users. I can fly planes to the limit of my vision, 2000ft or so, with even very cheap RC systems.

Whilst you say that more TX power is needed, is that really true ?

The very big danger with building in more power is that the vast majority of users would just abuse it. Then you get a situation whereby you now need to use large amounts of power just to overcome the amount of interference from everybody else who is using high power.

On the topic of the Hope RF modules, I have done a fair bit of work on the RFM22, for a satellite project.

The legal limit for license free use of the 433Mhz band is 10mW in a lot of the World, so I presume that would be the limit to be designed in.

At 10mW, the RFM22 will give you about 12kM line of sight for low speed data telemetry, and maybe only a couple of hundread metres in an urban area.
i agree with everything there. imo the most valid post in this thread so far. as you say 12km is a little optimistic except maybe for experiments in the stratosphere. in the real world i found 500m quite difficult for a standard rfm22b module with dipole. maybe 2x that with yagi or patch. it is my favorite uhf module though at half the cost and twice the range of xbee.

id mention the rfm23bp with 1w output but, like you, im a proponent of better antennas and protocols instead of polluting the spectrum with brute force power. so i wont mention the rfm23bp even though it has 10 more power than the one jake loves and costs 1/2 as much. so i wont mention it because, aside from illegal, no telling what the power mongers would do with it.
dave1993 is offline Find More Posts by dave1993
Last edited by dave1993; Jan 07, 2013 at 07:58 AM. Reason: note to self, do NOT mention rfm23bp
Reply With Quote
Old Jan 07, 2013, 07:45 AM
RC beginner
New York
Joined Oct 2008
5,622 Posts
Quote:
Originally Posted by Geoff_S View Post
Almost all of the major brands that are still offering modules in 2.4ghz have moved away from PPM (or PCM) communication between the modules and TX
yeah... right. like jake calling flysky a "niche" protocol. fyi ppm is still the ONLY protocol vaguely resembling a standard and is used in ALL plug-in modules. the only reason for using spi is cost reduction because thats the common chip-to-chip signal. universal for low cost and toy radios. for modules nothing will replace ppm. ever.

btw there also seems to be confusion over what pcm is. all modern radios use pcm over the air. it is defined as transmission via digital means as opposed to the old analog fm/am method.
dave1993 is offline Find More Posts by dave1993
Reply With Quote
Old Jan 07, 2013, 07:59 AM
Stuart
srnet's Avatar
UK, Cardiff
Joined Dec 2008
3,073 Posts
Quote:
Originally Posted by dave1993 View Post
as you say 12km is a little optimistic except maybe for experiments in the stratosphere. in the real world i found 500m quite difficult for a standard rfm22b module with dipole. maybe 2x that with yagi or patch
Indeed, the 12km would be LOS between two hilltops, the distance for real RC flying would be a lot less and a figure for ground level LOS is a more realistic figure to use.

I was getting around 200M, LOS with a RFM22B at ground level for 10mW, so 500M for 100mW would be about right.

The RFM23BP does indeed produce 10dBm more than the RFM22B, but its all or nothing, you cant turn the power down. That level of power (1W) would be illegal in the 433Mhz band in most parts of the world, and would very likely cause a great deal of interference to legal users of the band. A very bad choice for a RC device. Very power hungry to.

I liked the approach that GWS took with their small and cheap 2.4ghz transmitter which was released a couple of years back. Low power matched with a sensitive receiver, it was only for a park flyer, but had the great advantage that the batteries lasted a very long time indeed, about 70 hours from a set of 4 AAs.
srnet is offline Find More Posts by srnet
Last edited by srnet; Jan 07, 2013 at 12:20 PM.
Reply With Quote
Old Jan 07, 2013, 01:12 PM
Registered User
Joined Aug 2011
36 Posts
I absolutely agree that chasing ever higher transmit power levels is not desirable. Any modern additions to the commonly used parts of the radio spectrum must be smart about their use, starting with good sensitivity and great antenna design to get the task done with as little power as possible. Otherwise it becomes yet another tragedy of the commons.

How about security? Aside jamming (intentional or accidental), anybody with similar radio gear could conceivably broadcast compatible frames that our air units would happily obey if we don't encrypt our frames. AES is apparently easy to implement and very secure. Each frame then needs to be at least 16 kB, the size of an AES block.

https://www.silabs.com/products/wire...es/Si1000.aspx contains the application note AN324 concerning this, which claims that it is relevant for all Silicon Labs MCUs.
Helldesk is offline Find More Posts by Helldesk
Reply With Quote
Old Jan 07, 2013, 02:30 PM
Registered User
United States, ID
Joined Sep 2011
417 Posts
> The RFM23BP does indeed produce 10dBm more than the RFM22B, but its all or nothing, you cant turn the power down.

Where did you get this info? Certainly not from the datasheet. The module does 10dB-30dB in 3dB steps.

> im a proponent of better antennas and protocols instead of polluting the spectrum with brute force power.

Apparently not. From your posts it seems like you're a proponent of using mass produced, identical, hard-coded modules with no intelligent frequency control or power level management.

I highly doubt that you actually believe that adding 20-40 mW of power while also adding more receive sensitivity and intelligent channel and power level management would be a bad thing.

When expensive equipment, and potentially lives, are on the line I personally think it's highly irresponsible to have less power available than used with cell phone, wifi, or even bluetooth radios. Why should I use the LEAST powerful transmitter in my MOST important application?

I'm not sure where you get the idea that 100mW is a lot of power. It certainly isn't from comparison with any other type of common radio system. Looking around me I see at least a handful of RF devices in my living room. The 60mW TX module in my 9X radio is, by far, the LEAST powerful of them!

I've seen flyaways before. Even as a bystander, it's one of the worst feelings in the world. Besides the lost gear you have to wonder how far that aircraft is going to fly, where it's going to crash, and weather it will injure somebody, their property, or start a fire. Even electrics today can fly so far that there is NO safe flying area from which a flyaway could not escape, and both gas and LiPo craft have a chance of starting a fire when they crash.

If I were a regulator, I'd REQUIRE a minimum, adjustable TX power level with a reserve (higher) power level available to be used in case of emergencies or lost links.

This is where I'm coming from. Of all the radios I use on a regular basis, my TX has the least power and it's sitting in my most expensive gear. By comparison to the other devices I use (WiFi, bluetooth, cell phone, microwave oven leakage) 100mW is nothing.

If we got off on the wrong foot, I'm sorry. I didn't mean to insult you or your favorite brands. Let's put the past to rest and stop ripping on each other with facetious arguments.

> How about security?

The 3DR radio firmware uses a pseudo-random frequency hopping pattern based on the 8-bit radio ID number. It probably wouldn't take all that long to scan through all 256 possible codes for this, but waiting for a timing packet, synchronization, and checking for the data link would probably take some time.

I suggested they implement AES, but memory is tight after all the MAVLINK specific features they added. That can be gutted for our purposes, and the AES code is available from SiLabs. It only takes a few K of memory, so it shouldn't be too difficult to implement.

As long as we're talking about modules does anyone know if other companies besides HopeRF are making similar modules? I like the RFM22BP, but it doesn't have a MCU onboard. Anyone know of a MCU version?

I guess we could add a MCU, but the idea is to keep space and cost to a minimum by using the lowest chip/component count possible.
jakestew is offline Find More Posts by jakestew
Reply With Quote
Old Jan 07, 2013, 03:31 PM
Stuart
srnet's Avatar
UK, Cardiff
Joined Dec 2008
3,073 Posts
Quote:
Originally Posted by jakestew View Post
> The RFM23BP does indeed produce 10dBm more than the RFM22B, but its all or nothing, you cant turn the power down.Where did you get this info? Certainly not from the datasheet. The module does 10dB-30dB in 3dB steps.
I got this info from actually testing the device.

Not for the first time the HopeRF data sheets are wrong.
srnet is offline Find More Posts by srnet
Reply With Quote
Old Jan 07, 2013, 03:45 PM
Stuart
srnet's Avatar
UK, Cardiff
Joined Dec 2008
3,073 Posts
Quote:
Originally Posted by jakestew View Post
stop ripping on each other with facetious arguments.
Your justification seems to be that because a mobile phone, WiFi or a leaking microwave oven uses power X, then somehow its justified to use the same or higher power for RC model applications. Thats just plain daft.

Quote:
Originally Posted by jakestew View Post
If I were a regulator, I'd REQUIRE a minimum, adjustable TX power level with a reserve (higher) power level available to be used in case of emergencies or lost links
And it would be inevitable that the vast majority of RC users would leave the higher power on, even when its clearly not needed, 'just in case'.

Anyway, if your planning for the system to use 100mW to 1W in the 433Mhz band, what disruption would you expect this to cause to other devices that are legal users of that band ?
srnet is offline Find More Posts by srnet
Last edited by srnet; Jan 07, 2013 at 04:08 PM.
Reply With Quote
Old Jan 07, 2013, 03:52 PM
RC beginner
New York
Joined Oct 2008
5,622 Posts
Quote:
Originally Posted by srnet View Post
I got this info from actually testing the device.

Not for the first time the HopeRF data sheets are wrong.
i suspect the silabs rf chip does have programmable output like all the si44xx series but the class c amp does not reflect this change in level.
dave1993 is offline Find More Posts by dave1993
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Mod my 7CAP or buy a new cheap radio to use FRSKY system? OrlandoP Radios 2 Jul 18, 2011 05:12 PM
For Sale Werks Racing .28 Ceo Mods/Trx 3.3 Engines FT/FS Jamminracer18 Cars - Cars and Parts (FS/W) 1 Apr 18, 2009 11:17 AM
Build Log Project Gatika, Modern Voith Tug yacht boy Scale Boats 198 Feb 19, 2009 04:05 PM
Sold modded mini t arr for sale "cheap" or trade for mamba system jessnlaurie Cars - Cars and Parts (FS/W) 2 Oct 28, 2005 10:03 PM
FORMOSA project! Cheap, over 1:1 power system PunkerTFC Foamies (Kits) 12 Jun 16, 2005 08:45 AM