Linux Infrared HOWTO
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# 5.6. Beyond IrDA

## 5.6.1. Extending Transmission Distance

According to the IrDA specification the range is up to 1 meter. From the "IrDA Data Link Design Guide" p. 20 by Hewlett-Packard : " In some cases it may be desired to increase link distance beyond the 1 meter guaranteed by IrDA. The two ways to do this are to increase transmitted light intensity, or to increase receiver sensitivity. In order to extend the link distance, both sensitivity and intensity must be increased for both ends of the IR link. If it is desired to communicate with a standard IrDA device that may have minimum transmitter intensity, the receiver intensity must be increased. The standard IrDA device may also have minimum receiver sensitivity, so transmitter intensity must also be increased."

Andreas Butz wrote: "This might be a silly question, but has anyone an idea whether the whole IrDA stack really relies on a two-way connection, or whether there are some parts of it that could be abused for a one-way connection, ideally for unreliable data? We're trying to modify some IR dongles to broadcast information to palm pilots over several meters distance (cover a whole room), and since we don't want to modify the pilots themselves, and increasing the sensitivity on the receiver side seems unlikely to work, we're stuck with a one way link.". Please see the mailing list archive for details of the discussion.

Sent by Marc Bury " .. just heard about some Philips new scheme for remote controls: they call it IRDA - Control. This is supposed to be bi-directional, 75 kbps data rate, multiple simultaneous devices (up to 8) and with a minimum 6 meter range!" More information at IrDA.org .

The German magazine ELEKTOR issued a guide to build a Long Distance IrDA Dongle (20m, RS232, IrDA 1.0), ELEKTOR 5/97 p.

"The main problem is that you generally have to make the receiver more sensitive. Basic physics has the inverse square law: the intensity drops with the SQUARE of the distance, so going from 1 to 5 meters requires 25x the power (and battery drain on a portable device), or 25x the sensitivity (and dynamic range - it still has to be able to work at 3 inches). And if you want to do it on the other end, it doesn't simply have to be 25x more sensitive, it must pick up the tiny IrDA pulse needle in a haystack of florescent lights, screen savers, moving shadows ..."

Also laser diodes (pulsable) were recommended by K-H. Eischer: But they are more expensive. And the laser diodes are also dangerous if they have more than 1 mW. A better solution would be to use lenses to focus the beam. There is a minimum of absorbtion in the air (I don't know the right frequency) and you should use IR diodes with this frequency.

James wrote: " Who ever it was wanting to do long distance with IrDA, we've tried this before. The best approaches are:

- wavelan - buy the cards but not the antennas you can make your own with equaly good gain as the $9000 type they sell here.

- microwave - you can pick up X-band doppler radar modules, tune them slightly apart and use the your local TX as the LO for the incomming RX, the whole thing behaves like ethernet and you can hook it onto an AUI port, this may now be illegal.

- ir - Many people sell kits which transmit video over Ir, they come complete with the large fresnel lense you need, they manage about 4MHz b/w over 100m.

- laser diodes - when we looked at these they were a pain, I think elantec make decent drivers but modulating them was a big pain, Steve Carcia had a series on articles on modulating He-Ne lasers but be careful they have lots of volts in them that want to get out and kill you.

Whatever you choose IrDA might very well be a good choice for a protocol, given it's one of the few that sensibly copes with simplex."

Here are some links to do-it-yourself InfraRed (IrDA) devices to use with your laptop, notebook, PDA or mobile phone.

## 5.6.2. Upcoming Standards (Bluetooth and IrDA)

"More and more people now think that IrDA and Bluetooth will live happily side by side, and the idea of Bluetooth as the IrDA killer just don't work anymore. IrDA is still unbeatable in price/performance and with the new additions to the standards family like AIR and VFIR, it's really good to see that IrDA is moving in the right direction."

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