Hi,
I'm looking for a wireles serial radio-link that runs Full-Duplex. Does any one know about one out there? It's for a mobile application, hence size and power consumption should be ideally as little as possible while coping with distances of at least up to 400 metres.
thnanks. stefan
What Aerocomm modules did you use? And what kind of throughput and latency were you getting?
What is the datarate that you will need? If you want really Full-Duplex on the air you will need two independent radiolinks (in case of a high troughput you may need this anyway)
If your datarate requirement is low enough a duplex link that emulate full-duplex as seen from either should be OK?
HTH
-- ---- Morten Raider of the Lost Electron
I used AC4490 -200 on 9600 Baud. It is installed inside the box on a pole. The device counts KYZ energy meter pulses and sends replies on modbus-like packets once in 5 minutes. The length of a packet is about 32 bytes.
found it
If you really need full-duplex you need two separate radio systems working on two separate frequency bands. In which countries should this system be usable (frequency allocation) ?
If you insist of using a single frequency band,be prepared to use duplex filters, which are big, heavy and expensive.
What data rate do you need ? What reliability do you need, 90 %,99 %, 99.9 etc of the time ? Do you always have a line of sight path to the mobile unit ?
Depending of these factors you may end up in a power consumption of several watts.
Paul
It'll run it in Europe (UK and Germany). The full-duplex is basically desired to ease the protocol as collisions can't occur if both ends want to send at the same time. I use the radio-link to control a model helicopter and would like to have real time behaviour.
That is not acceptable in my relatively small helicopter.
The data rate is not crucial. As little as 4.8kb/s or even 1.2kbaud would do.
the higher the better :) As a 100% are impossible anyways the protocol needs to handle lost packages. A reliability of above 90% seems ok to me.
The heli will be operated obviously outside but a tree inbetween shouldn't be a problem.
Thanks a lot.
The datarate is not critical. As little as 1.2kbaud would be ok.
Having an emulated full-duplex makes the protocol more difficult and I ideally would like to have some real-time behaviour.
Thanks, Stefan
Well if you are using it to control and feedback from a model helicopter then in UK you can ONLY use these bands, as this is classed as a Short Range Radio Device
To control the model
40MHz AM/FM (NOT allowed for airbourne models) 70MHz FM (ONLY for airbourne models) 459MHz FM (for any model)For feedback (telemetry) from the model
433MHz FMThere are restrictions on transmitter power, see IR2030 document on
Using other bands and other power levels will not go done well, with many people and could land you in some cases with large fines and/or prison.
There are several lightweight modules available to do this even at low data datas 4.8KB and below without extra modem chips. It is possible to make a simple board with lightweight and battery powered transmitters and receivers. I have done it for a completely different project using 459MHz and 433MHz.
See CDP series
Both have either switch selectable or programmeable channel selection, see examples on
See
Using these modules on two bands will be an example of the easiest methods, to get higher reliability. Both units are metal cased.
Put a Radio Ham transmitter next to the 433MHz receiver and the 433Mhz only got about 2% distortion on a sinewave transmission when the tip of the
459MHz was less than 2cm from the PCB on the underside of the receiver!
That would depend on the tree, time of year, and of course whether it has been raining......
These sorts of modules have evry low power consumption, because they are meant for Short Range Radio Devices that have limited range and limited battery power.
Your model helicopter is probably using 70MHz already, so your simplest solution is add a 433MHz telemetry channel to the model.
--
Paul Carpenter | paul@pcserv.demon.co.uk
Main Site
GNU H8 & mailing list info.
For those web sites you hate.
The ATMEL ATR2406 seems to be close to what you need, except for the range of 400 meters. You can add an external RF amp & transceivers.
--- Quote from ATMEL ---
The IC is manufactured using Atmel's innovative SiGe BiCMOS technology and packaged in an ultra-compact QFN32 plastic package (5 x 5 mm). The low-IF receiver architecture enables low external Bill of Material (BOM) costs, while offering a superior RF performance. The high receiver sensitivity of -93 dBm and high output power of up to 4 dBm enables link ranges of up to 70 meters. The transceiver supports data rates of 72, 144, 288, 576 and 1.152 kbit/s and offers receiver signal strength indication (RSSI) as well as a digital clock recovery.
The ATR2406 interfaces seamlessly with Atmel's AVR Flash microcontrollers and allows for the design of a complete chipset solution for ISM applications. While being operated alongside the AVR microcontroller, the average current consumption in typical low-data rate applications is less than 5 mA when operated in burst-mode. This complete solution offers the best combination of low cost and low current consumption while leaving designers maximum flexibility. Atmel's Marketing Director for Communications products, Uwe Barthelmes, stated, "Using the ATR2406 RF reference design and complete AVR software drivers available from Atmel, interfacing to the AVR is as easy as sending data to a UART."
Samples of the ATR2406 in ultra-compact QFN32 plastic packages (5 x 5 mm) are available now, pricing starts at US$ 1.80 (100 k). High-volume production will start August 2004. A complete evaluation kit including reference designs and RF protocol firmware to simplify the design are available. The development kit ATR2406-DEV-KIT is priced at US$ 500 and can be ordered via Atmel's local sales offices.
Take a look at this little nifty device:
I should contain everything you will need for your telemetry/control of the helicopter. (The 433MHz band in Europe is fairly open - but you will need to check with the appropriate rules regarding control of toys)
The respons you are looking for, as in real time control of a RC Helicopter, will not be detrimented by a turnaroundtime less than 10ms. I believe that low weight is more important that a couple of extra bytes in the protocol?
The range you want is in the best conditions possible, you have practically line-of-sight and a proper choice of antenna should give you the link budget you want.
HTH
-- ---- Morten Raider of the Lost Electron
IMHO, anybody trying to use a shared frequency band for _control_ of a model aircraft or other flying device should be put behind bars to think what he/she is doing !!
If other legal signals on that frequency band disrupts the control link for say, a few minutes, it is quite likely that the aircraft goes out of control and may hit someone in the head with disastrous consequences.
For instance, if some LPD (10-100 mW) is used for a control link on the 433 MHz band which is also used by radio amateurs, it is quite likely, that the control link may be interrupted by amateur radio transmissions, especially since the 433 MHz range is used for the mobile to repeater transmissions in many countries. A mobile amateur radio transmitter, which are typically 30-50 W or about 30 dB more than the LPD, may block the control link when moving in the neighbourhood.
Use proper frequency bands specially allocated for model control to control the helicopter.
Using some other band for telemetry will also solve the duplex problem. If a shared frequency band is used, the downlink could suffer interference from other legal users of the band, so this must be considered, when designing the system.
Paul
As the OP wants to fly his model in the UK, it would be worth mentioning that Ofcom, the UK regulating body, has a dedicated band around 35 MHz for flying gadgets. 433 MHz can be used to transmit data *from* the model. Some more details can be foud here:
HTH, Vadim
You can't put someone in jail just for thinking of trying something. He might own the entire 400 meters air and ground space. Even if he carry out the experiment and did some damages, he should be responsible financially. If he did not intend to cost such damage, he should not be in jail.
I wonder how many inventors would carry out their experiments if they risk going to jail for.
Like drinking a bottle of whisky and then driving around in a car without brakes :-).
Depending of the sped of the model aircraft, it does not require a long communication failure to fly outside even this area. 10-40 s should be enough.
The situation for a model helicopter may be different _if_ the helicopter goes into a autoratoation mode upon loss of command link and lands more or less intact close to the point of communication link failure.
What is the price of a dead person ?
I think "criminal negligence" is term used in the US.
My point is, why use a risky method, when there are other methods considered to be more safe (frequencies allocated for model aircraft control) ? Paul
^^^^^^ Flying Gadgets MUST use 70MHz band, 40MHz is for land/water toys.
--
Paul Carpenter | paul@pcserv.demon.co.uk
Main Site
GNU H8 & mailing list info.
For those web sites you hate.
There has been at least one court case after inquest in the UK of model aircraft losing control and killing a small boy.
There is a web page about it on the Radio Control Modelling group site.
They should always check what they are doing for safety and risk assessment many don't.
--
Paul Carpenter | paul@pcserv.demon.co.uk
Main Site
GNU H8 & mailing list info.
For those web sites you hate.
If you are referring to the accident in April 2003 on Dartford Heath in Kent then the model was unsafe to fly in the first place and it had nothing to do with the quality of the radio equipment. It was the structural airframe that failed.
And it was a girl.
Any link? The document I've pointed to (RA60) says "The 35 MHz is dedicated solely to aeronautical modelling." I couldn't find IR2030 document on the Ofcom site.
I am also curious because my son is tempting me to buy a helicopter. The last time I asked in the model shop the bands were 40 MHz for surface, 35 for air and 27 for any model.
Vadim
That's fine if he is driving in his own land without anybody around.
A well designed system should have emergency homing system and/or GPS.
What if he is testing communication link/control in high interfence situations?
Depends on how that person got into the test area.
Depends on the circumstances. Appearancely, you already found him guilty and handled down your sentense without any considerations.
Risk assessment is very subjective. Tell the Wright Brothers not to fly when driving is just as good.
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