Silly Infrared Question Time!

jazzed

Happy Easter to all who observe it!

I'm interested in adding an Infrared Transciever to a project. I have my eye on an IrDA compliant device since it's small and can be enabled on demand. IrDA devices are NOT modulated.

The question is: do you think it would be possible to modulate an IrDA device TX LED at say 40KHz to control a TV or talk to Parallax IR receivers with Propeller?

The answer may be: Yes. But what would be the benefit?

IrDA is used in USB dongles, so it could be a cheap programming solution on Propeller Portable devices. If not, that's ok since IrDA can be used for device-to-device communications. If IrDA can be modulated by Propeller so that TV IR receivers understand, that's one more big benefit since it also opens possibilites for home entertainment remotes and wireless Robotic control.

Any thoughts?

Leon

I can control my DSLR with a relatively slow low-end PIC using modulated IR, so it should be easy with a Propeller.

markaeric

There are several IR objects in the OBEX to receive commands from TV remotes, so there should be no reason why the propeller shouldn't be able to emulate remote controls, right?

Phil Pilgrim (PhiPi)

jazzed,

Can you provide a part number for your IrDA device?

-Phil

jazzed

Phil Pilgrim (PhiPi) wrote: »

Can you provide a part number for your IrDA device?

Vishay TFBS4650

Searching obex for irda returns no results.

Phil Pilgrim (PhiPi)

I don't see anything in the datasheet that would prevent you from doing what you want. If you use the device for receiving, though, it won't do the demodulation for you. For that you'd have to use something like my Goertzel object or an I/Q synchronous detector to do the demod.

-Phil

jazzed

Phil Pilgrim (PhiPi) wrote: »

Iuse something like my Goertzel object or an I/Q synchronous detector to do the demod

Thanks Phil. Got links?
Demodulating TV IR would be useful for "learning" a command stream and communicating at lower baud rates with other devices. Wish I had room for a through-hole IR receiver on the motherboard, but things are really tight ....

Phil Pilgrim (PhiPi)

Here's a link to the Goertzel object:

http://forums.parallax.com/showthread.php?115805

My AM receiver object demos the synchronous I/Q detection technique:

http://forums.parallax.com/showthread.php?p=914552&viewfull=1#post914552

as does the Bell 202 modem:

http://forums.parallax.com/showthread.php?110918

-Phil

JonnyMac

Demodulating TV IR would be useful for "learning" a command stream and communicating at lower baud rates with other devices.

This may be helpful (very easy stuff):
-- http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/prop/col/nvp4.pdf

jazzed

JonnyMac wrote: »

This may be helpful (very easy stuff):
-- http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/prop/col/nvp4.pdf

It's much easier to do with an IR receiver that does the decoding for you.
I just don't have room or power budget for one of those. Thanks for the suggestion anyway.

Looks like my candidate IR transceiver is only good for a couple of feet. Guess I have no choice :<

JonnyMac

Is IrDA modulated? If not, it should be a matter of devoting a PASM cog to the decoding of the bits. Am I way off somewhere?

jazzed

JonnyMac wrote: »

Is IrDA modulated? If not, it should be a matter of devoting a PASM cog to the decoding of the bits. Am I way off somewhere?

IrDA is not modulated. It works like a UART somehow. I'm attracted to it because of broad support with hand-held devices and USB connectivity.

Unfortunately, the IrDA range is very limited, so either I find a good modulated solution, or I punt and go with what I spent the last couple of hours squeezing on my board. The chip I mentioned has a shut-down which tri-states the RX output ... very attractive for sharing P31 with FT232 or PropPlug.

GordonMcComb

IrDA is modulated in the sense that it is encoded. It's not transmitted on a carrier. It's not a simple matter of just looking at highs and lows and making those bits. I am recalling that most IrDA implementations use a return-to-zero modulation.

jazzed

Thanks for the clarification Gordon.

Here's an app note that talks about using IrDA transceivers as a remote transmitter effectively at > 10 meters.
http://www.vishay.com/docs/82606/remote.pdf Apparently my first choice is very low on the ladder of ability.

They do mention learning remote codes briefly. Would be nice to know more about what they mean.
There are other app notes on the vishay site.

Interesting stuff on the vishay site. This blurb shows up in the standards section: "IrDA Object Exchange Protocol OBEX(TM)"
Link specifications are here: http://www.vishay.com/docs/82513/physical.pdf

GordonMcComb

Those are all old parts, so maybe the have something more recent with better specs. Any range greater than 15 feet is a bit of a lark anyway (maximum practical room size), unless it's planned for use in an auditorium or something.

Does it *have* to be IrDA? If not, I wonder if you couldn't get the range you want by cranking out the current to a high output IR LED using your own encoding.

jazzed

GordonMcComb wrote: »

Does it *have* to be IrDA? If not, I wonder if you couldn't get the range you want by cranking out the current to a high output IR LED using your own encoding.

It doesn't have to be IrDA, but the solution is compact enough for my assembly, the RX driver can be turned off in shutdown mode, and vishay claims 9M transmit range for TV remote applications on some devices.