Need a FSK long range transmitter

[anonymoussomeone]

Hello everyone,

This is my first venture into microcontrollers and am new to robotics. I am and electronics and communication engineering student and am making a project on "Long range RF remote controlled car using computer as control input".

As my minor project, I want to implement dc Motor control wirelessly.
I have ATMEGA 16 microcontroller and its board with 4 ports.

I have decided to use FSK transmission for RF part and am in a lookout for viable ICs for that purpose.

I have found a few options from AMTEL namely
ATA8404
ATA8405

 and CMX017 UHF FM/FSK Transmitter from another source.
I have done basic AVR programming before and know C language.

The problem is, the datasheets don't give the range of these transmitters.
So could somebody help me out on this and also brief me on calculating range for RF transmitters? Though we have Antennas in our course this sem, but it would be good to know beforehand.


Help and suggestions regarding any part of the project are most welcome and please, its urgent.

[dunk]

hi,
so all the single chip solutions i've ever looked into tend to have a very short range on their own.
many are intended to have additional RF amplifiers between them and the antenna.
if you need more than a few 10s of meters range you will probably need an amplified solution.

since time is an issue i recommend you look into pre-made RF modules. this will simplify the process greatly as they will have all the hard work of picking an RF chip, switch (if its a transceiver) and amp that work together providing you with a simple interface. (typically UART or SPI.)

some questions that will help narrow down the search:
one way (TX and RX) or 2 way (transceiver)?
desired range?
indoor or out door?
what country are you in? (this will affect what bands you can transmit on.)
any other restrictions on frequency?
is there much other traffic on that band in your area?

after that, search through DigiKey for RF modules.
it's hard to get expected ranges for some of these modules but the manufacturers always specify the TX power out put and RX sensitivity level.
so if you find a datasheet that does have a published range, make a note of the power TX level, the RX sensitivity level and the frequency so you can get a ballpark idea for other modules.

i've some notes on using some transceiver modules here: http://sites.google.com/site/mrdunk/ but it's not really complete yet as i'm still getting a lot of interference from other 2.4GHz sources.


dunk.

[anonymoussomeone]

I am living in India,
The bot is meant for surveying purposes. So its probably an outdoor bot. The range should be large, at least 500 meters. Right now I am looking for Transmitters and receivers.
But I am also planning to expand it using a transceiver, once I complete the receiver and transmitter part successfully.

Thanks for the information. Am going through your suggested page.

[Pratheek]

Try Zibgee. They are quite popular so you will definitely find information on using them on the net.

[anonymoussomeone]

I searched for the Zigbees and it seems that they are available for 2.4 GHz range.

But I also read that for longer transmission range, lesser frequencies are employed. So I was thinking of narrowing on 433MHz transceivers.
Now would somebody tell me if video can be transmitted over this frequency range or not.
What ranges can be achieved from 2.4 GHz transceivers?
and would ATMEGA16 be enough for this task. I intend to use AVR based microcontrollers only.

[madsci1016]

I searched for the Zigbees and it seems that they are available for 2.4 GHz range.

They also have 900 Mhz.

Is 40 miles (65 Km) enough range?

http://www.sparkfun.com/commerce/product_info.php?products_id=9411


And there are 900Mhz video transmitters, I don't know of lower frequency video transmitters

[Razor Concepts]

This is difficult because the receiver is on the car, which is at ground level. Maybe look into cellular frequencies. 2.4 gig, 433, etc etc may work well if the receiver is in the air where there are no obstructions, but on the ground with buildings and such, it is much more difficult

[anonymoussomeone]

Thanks for that link, but its too costly for a beginner project....though I have high ambitions and expectations.....

So you mean to say that I should opt for 900MHz FSK transceivers, as they support 115kbps data rate, and what about range.....I am sceptical about cost factors also.

[madsci1016]

Why don't you tell us what range / data rate / cost you are looking for?

[anonymoussomeone]

Actually, I have an ambition to make the project, but am lacking on resources......so to be short and precise I know that I want to achieve the following objectives:

1. Range: at least 500 meters.
2. Support for Video transmission, and am not quite sure of what data rate I need for a live feed. Probably I need a transceiver with full duplex   mode.
3. I have ATMEGA16 microcontroller and its basic board with 4 ports on it. SO I want to put it to good use.
4. And in Indian currency, I want to keep it as low as possible. Highest budget is Re5000/- which approximates to $100/-
5. I wish to make it ASAP.

[madsci1016]

So you want to be able to send motor commands and get back video over the same wireless link?

[anonymoussomeone]

for now, this is exactly what I intend to do. Please shed some light on my little ignorant brain.

[dunk]

So you want to be able to send motor commands and get back video over the same wireless link?

for now, this is exactly what I intend to do. Please shed some light on my little ignorant brain.

what you are asking for here is not at all easy.
video and motor commands require 2 completely different sorts of data link.

the only practical way of achieving this within budget that i can think of is have 2 separate RF links running on different wavelengths.
use a data-modem type device for your control data
and use a separate dedicated video transmitter on the remote device to send back video.
the 2 different transmitters must be operating on completely different wavelengths if you want to avoid interference.

this method can be achieved using "off the shelf" equipment too:

FPV RPV na varanda - FPV on the balcony

i can think of two other methods to look into using a single RF link. (neither within your budget or single AVR microcontroller requirements.):

put a miniature PC type device on either end connected with wifi and directional antenna to acheive the desired range. then just stream video back over the wifi link.

use a tranceiver type device for your control data then digitise single frames and send them back over the data link.
this would not give real time video but for a slow moving remote device it would be usable.
this method could *nearly* be achieved on a single AVR at the remote end. read up on CMUcam and AVRcam for an idea of just how complicated this method would be.


dunk.

[gaurav.p]

REMOTE CONTROL PART:-
here's my idea connect use two avr's and from the first one connect some buttons(and obviously program them) to act like a remote and then transmit the data from it to the rx Rf module of the second avr chip,which will be on ur bot .
VIDEO PART:-
well use this http://robokits.co.in/shop/index.php?main_page=product_info&cPath=11&products_id=235 and ask the vendor on the wavelength of operation of the camera and simmilarly chose a different wavelength other than with which the camera is operating.

So here's d solution.i hope it will work .if i m wrong,correct me.on the point of 500m operation range, u can upgrade to Xbee Pro(range upto 1 mile)otherwise i advice to use a smaller range rf module coz u r tight at ur budget.

Regards,
Gaurav