# Reliable Transmission Method?

1. Jun 26, 2010

### Lancelot59

A friend and I are planning to build a remote controlled vehicle, probably 4 wheeled. We want to be able to operate over the distance of about a block, which isn't incredibly far. The tricky part is that we need it to be able to send us back audio and video, along with being able to receive control inputs from such a long distance. Forgetting the complications of designing the hardware to process all of this for the moment, what is the most reliable way to move all this data around? Could a RF setup handle all of it?

2. Jun 26, 2010

### stevenb

Yes, low GHz carrier frequency modules are readily available to provide about 50 m of transmission distance at many hundreds of Mbits (edit: I meant kbits) per second. It's not a trivial project though. You probably need compression and limitations on audio and video bandwidth.

Last edited: Jun 27, 2010
3. Jun 26, 2010

### mgb_phys

Audio and video mean a lot of bandwidth, so unless you have government/military backing the only thing that doesn't need lots of licensing and uses of the shelf is likely to be wifi - anything with a decent antennae shoudl work over that sort of range - at least if you have line-of-sight

4. Jun 26, 2010

### Lancelot59

It's really just gonna be a toy/a platform to test things out on, so I don't think licencing will be a huge concern.

The video just needs to be good enough so I can see where I'm going. The audio would be more so I could drive the thing up to people and scare them. It wouldn't be active all the time.

I considered Wi-Fi, but the issue is line of sight. I won't always be able to see it. Plus a tree or car could get in the way. Also wouldn't that be harder to work with than RF? Most of the off the shelf applications are meant to go directly into computers.

5. Jun 26, 2010

### mgb_phys

You can use simple unlicensed 419MHz transmitters for the video.
The sort they sell for wireless baby monitors or spy cameras, they cost $20 and broadcast to a little receiver box. But they are only going to work 20-30m even outdoors - you might do a little better with a more directional antennea pointed at the car. Or you can have a webcam on the car sending wifi, should be good for 100m with a decent antennea costs$100.
Line of sight is best, a few trees aren't going to matter, going through 100m of concrete+metal buildings isn't going to work.

Then most expensive is to use GSM and the cellphone, unlimited rage but is costly to build and use

6. Jun 26, 2010

### Staff: Mentor

Wrong. The point is that you need to stay within the FCC rules (or whatever govenment rules cover the country where you live). There are important reasons for those rules, not the least of which is avoiding interference with emergency services radio traffic.

Your best bet is to use an iPhone or some other standard way of transmitting data and video over the existing infrastructure. And you might want to reconsider your goal of "scaring people". That will likely result in a wrecked vehicle and a lawsuit against you. Not smart.

7. Jun 27, 2010

### Lancelot59

Yeah, GSM is a bit out of my price range. If I get one of those RF transmitters, I wonder how easy it would be to boost the range. Put a signal amplifier in line to the antenna?

Good point. Although it's just a simple matter of looking up the restricted frequencies for this area and using something else.

Well not scaring people per-say. More as in being able to talk to people through the machine. The goal is to be able to drive this aroaawund my school campus, and get people to push elevator buttons. I would use Wi-Fi if that was the only goal, but the campus has huge holes in the wireless network, and driving through one of them would be pretty bad.

So I guess I'll be going with a RF machine, although I could do a combination of RF and Wi-Fi so the option is there if it can be used. The big university here has coverage all over the campus, so if I head there I could drive it anywhere.

8. Jun 27, 2010

### Staff: Mentor

Wifi doesn't need to be line of sight, it just helps if it is.

9. Jun 27, 2010

### mgb_phys

No the free license limits the power, if you boost the power you will interfere with every intercom, baby monitor, car alarm for miles.

wifi doesn't need to be line-of-sight but the poster was talking about a city block which is approx 100m (?) so pushing the limits of a non-directional antennea