Hi,
anybidy had tried out with robots transmitting Audio/Video Over any media? I need some ideas on interfacing the A/V to a RF modem so that i could transmit and A/V along with data.

any inputs? replies are appreciated....

regards,
abhay

 

Im not sure on how you would hook it up to an RF modem, but i do know that you can get those Nanny cameras, they are small you can get them with sound, video, some with night vision and they transmit over RF to there own reciever.
Make sure to find one that wont interfer with your radio control signals though

 

You can buy commercial A/V senders, in the UK they are about £40GBP.
Fitted with a selection switch for 2 or 3 channels.
Short telescopic aerial, range about 15 to 20 metres, good quality.
Fitted with A/V connectors.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

Hi,
Thanks for your reply... this one i tried out.... but the range is limited.... BTW do you came across any solution to embedded onscreen data on the video.. say i need to show the speed on the screen along with the video....

replies are appreciated...

thanks,
abhayadev s

 

What sort of range are you looking for?

__________________
Bill
Smart Kits build Smart People
http://www.blueroomelectronics.com

 

may be 500m to 1KM, i think i should go for any professional RF transmitters

 

hi,
You can get upto 1Km Line Of Sight, with some A/V transmitters, using an expensive dipole aerial.

For adding extra text to the transmission, units are also available, look thru the 'security CCTV' web pages.

Depending upon the country you live in, power radiation regulations do apply.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

thanks for the info.. i think i could use any module which supports the text as osd over composite video...

 

If you need to send data those A/V senders usually have 2 audio channels. You could use one for audio and the other for data. 15Khz bandwidth is fine for 4800 baud comms, it will need to be DC balanced though. And if you're really savy with microcontrollers you could use mulilevel signalling to increase the datarate..because the A/V senders are analogue.

Blueteeth

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Inconsistency is the key to flexibility!

 

thanks for the suggestion, may i get some more info regrding the idea.... how will u pump serail data over audio channel... etc....

thanks in advance...

regards,
abhayadev

 

Sure, for hardware you'll need to convert 0-5 TTL (from a microcontroller/UART) to 1v p-p for the A/V audio input. I wouldn't worry too much about input impedence, a simple transistor buffer would do, although I guess a simple voltage divider would be ok. Firstly, convert the 0-5V to 0-1V using a simple voltage divider. Then the output of this through a DC-blocking cap (make it say 10uF) to give you 1v peak-peak AC.

Normally when sending 'digital' over a bandwidth limited analogue channel, one would use pulse shaping, or a low pass filter to cut the high frequency harmonics off the square wave...but thats only if you want to get the maximum possible datarate for the channel. Its usually 15-18kHz, and as I said, 4800 baud would be fine for that, so I wouldn't bother with any form of low-pass filter...the channel will 'round-off' the edges of the sqaure wave anyway.

The receiver, would need an amp preferably with a schmitt trigger as a dataslicer, to get 0's and 1's from the AC signal with the minimum off errors. Again, to keep parts to a minimum, you may be able to get away with a simple transistor buffer.

Now, software. This is a bit trickier because we're sending data over a channel designed for AC, so any DC component will be lost. For this I would recommend using 'manchester encoding' I believe Nigel Goodwin has some excellent tutorials for this. You can use a hardware UART from a microcontroller to do most of the work for you. I would recommend a packet structure like the following:

<preamble><syncheader><payload><endoftransmissio n>

preamble: say 8 bytes of alternative 1's and 0's. This wil get the UART in the reciever ready for syncronisation.
Sync header: Tells the reciever that the next byte will be data, marks the end of the preamble,
Payload: your data
End of transmission: just tells the reciever its finished sending stuff.

For the reciever...using a hardware UART isn't easy. But, for 4800 baud, it would be fairly simple (again using nigels tutorials) to recieve the data using a PIC micro.

As I said before, you can of course make it more complicated, and increase the datarate, adding error detection/correction, but unless you're sending a hell of a lot of data, its completely unecessary For example, I've used the 'video' channel in an A/V sender for data, up to 3MB/s 2 level encoding, and 16MB/s for multilevel. The latter was a vastly more complicated.

Hope that helps, I'm sure I read a similar post about doing this on a RC plane model forum somewhere, I'll see if I can dig out the link.

Scott.

__________________
Inconsistency is the key to flexibility!

 

Hi,

Thanks a lot for the detail,i will be back soon....

thanks once again

regards,
abhayadev s