Broadcasting wireless direct from the chip

samsn4

Anyone working on this?

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Daniel Mueth
WSIU-TV Master Control

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"Just plug it in and let's see what happens"

Mike Green

What did you have in mind? The Prop already does ok on the lower VHF channels with a short whip attached to the TV output (best quality with a 6MHz crystal instead of the stock 5MHz one ... because of PLL jitter vs. 6MHz channel spacing). A matched bandpass filter and resonant whip wouldn't hurt.

Post Edited (Mike Green) : 11/5/2007 6:14:34 PM GMT

samsn4

Instead of have a cable out to a tv or vga monitor,·Tx out to a TV ch 3 or 4.·

example application:
Home security system based on the prop, the home owner will be able to view the status of and any action that has happened.

thanks

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Daniel Mueth
WSIU-TV Master Control

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"Just plug it in and let's see what happens"

Mike Green

It works. Like I said, it works better if you substitute a 6MHz crystal for the supplied 5MHz one and if you use some filtering and a proper antenna, but I've used the stock Demo Board on channel 3 with a couple of inches of antenna plugged into the video output jack a short distance (a foot or two) from a TV. You have to change the parameters in tv_text.spin to use broadcast rather than baseband mode and to select the proper frequency.

The carrier frequency is not a multiple of 5 MHz, so I just made it so (60MHz) and the TV's AFC adjusted.

Read the comments at the end of tv.spin which is included with the Propeller Tool. I'd set the carrier frequency to a multiple of the crystal (like 55MHz for channel 2) to minimize jitter and turn off color for the best image. Play around.

Rayman

I didn't realize this worked! Thought I read that it didn't... Maybe that was because of the crystal. Think my 6.25 MHz crystal will work? Or, do I need 6.00

Mike Green

Rayman,
It works (sort of) even with the 5MHz crystal, but there's a lot of jitter that looks like noise on the screen. The problem is that the crystal is not an even submultiple of the video carrier frequency. With the counter's PLL, there's a slight variation from cycle to cycle of the frequency of the carrier as the PLL tries to provide, on average, the requested frequency. The low VHF video channels are on a 6MHz spacing which works out great with the 6MHz crystal. With a 6.25MHz crystal, try channel 3 with a carrier frequency of 62.5MHz or channel 4 with a carrier of 69MHz. The actual channels are 54-60MHz, 60-66MHz, 66-72MHz

rjo_

Rayman,

There are lots of opinions floating around about what will or won't work in all kinds of contexts. And there are lots of critics about just about everything... but the real truth is that you can do just about anything with one or more Propellers. You can take that to the bank. Lots of people know other ways to do things... that's fine, but most of the time the answer is ... if you really need to do something (to put a signal together or take one apart) and all you really know is the Propeller... you know enough.

For that to be true, however, you have to become a flat out expert. As you know, but others might not, Baggers is just one of the guys blazing the trail in terms of this kind of technical innovation (to which we should all aspire.) He's doing synthesis right now, but analysis is on the flip side of this kind of thinking.

I looked through your web site and then promptly lost your link. Very, very impressive. Please post it again.

Rich

Rayman

Mike:· Thanks.· I don't know if I need broadcast, but it's too cool not to try!

Rich:· http://www.rayslogic.com/propeller/propeller.htm

scotta

Can you broadcasting data using similar hardware techniques ?

Mike Green

Theoretically you could do frequency shift keying at radio frequencies to transmit digital data, but you could get a much better quality (and more reliable) signal using an external radio.

deSilva

rjo_ said...
... but the real truth is that you can do just about anything with one or more Propellers. ... if you really need to do something (to put a signal together or take one apart) and all you really know is the Propeller... you know enough

I should like to add: You also have to know a little of the "domain" you are exprimenting with.
I would be useful to know a little bit about RF, TV conventions, laws, EMI... before transmitting HF. It would be nice to understand Nyquist and low pass filters before adding an ADC; it would be a good thing to know Ohm's law before connecting anything to the Propeller at all Those ar just a few examples.... No one special in mind...

Paul Baker

This is all thats required hardware-wise to get the broadcast to work:


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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

Jo

And that, ladies and gentlemen, is why I love the propeller: a wire and some resistors on a Propeller acomplishes something that on almost all other microcontrollers requires extra hardware and ingenuity.

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Jo

Fred Hawkins

? why does Devo's Whipit come to mind?

deSilva

Principles of Mathematics: A whip - like an aerial - works by allowing a stationary wave to form by resonant effects in accordance with the length of the device. Physics are different, but the underlying strcture of the first principles is similar (second order partial differential equations - love them!)