Hi,
I couldn't find my answer in any of the other threads. I am curious as to what measuremnet is used to describe the strength of an IR signal. I realize that IR is limited to line of sight but I am trying to go as far as possible.

Thanks
Russ

hoggre@hotmail.com

Me again,
wow I seem to have stumped the crowd. I am trying to get another rumor explained away. I was recently told that an IR device that is to powerful can actually burn up a receiver. Is there any truth to this? If noone can answer my previous questions does nayone know where else I could look?

thanks for the great site and lists

Russ

Russ,

Strictly, the unit of measurement for IR power is Milliwatts per Steradian (mW/Sr). (Corresponding receiver sensitivity is expressed in milliwatts per square meter.) This value can be used when comparing the paper specs of one IR emitting diode to another.

However, mW/Sr is not an easy value to measure and also does not take into account efficiency (or lack thereof)of whatever modulation and encoding scheme is used to place data onto the raw IR signal.

Many consumer electronic equipment manufacturers thus end up using a more empirical approach in qualifying their remote control systems: They specify perfomance in terms of maximum distance achieved when sending a specific code to a calibrated standard receiver in a known ambient environment. In other words, they do it the old fashioned way -- by experimentation. (Most specs, by the way, call for a range of around 7 to 9 meters straight on and something less from an angle).

I don't know exactly what your application is, but if you are building your own transmitter, keep in mind that IR LEDs come with different conical dispersion patterns, ranging from about 10 degrees to about 30 degrees. The narrower paterns will give better range at the expense of having to aim more accurately if you are close up. Diodes also come in several IR wavelengths - be sure the one you use matches the receiver's peak sensitivity. Consumer entertainment equipment does NOT generally use the same IR wavelength as IrDA! (These are close enough that one can be seen by the other, but range will suffer.) After that, all that's left is to pulse as much current through the IR LED as you can, and/or put several in series.

As far as burning up receivers goes, I have never heard of that. I suppose if you aimed a laser at an IR receiver you might cause some damage, but with a conventional remote control you'll fry the transmitting IR diode long before you can put enough current through it to cause any problem. What *is* possible with a powerful IR transmitter is that it might swamp the receiver when you are close up -- i.e. your "turbo" remote will only work from, say, 6 feet or more away. But that shouldn't cause any permanent damage.

Alfaman.

Thanks,
actually I'm mostly just trying to gain understanding. eventually I will try to control some lego mindstroms creations with my palm III. I am looking into the add on IRDA peripheral because the palm IIIs built in IRDA is so weak.

Basically I am trying to decide, cost regardless, of wether or not it is worth it to buy a fancy remote to use with my overgrown toy. The Palm add on sems to do everything I need. Macros, decent range etc. Thanks for the explanations.

Russ

Me again.
where can i find a run down on relative power of different remote. comparing and contrasting angle and distance capabilities.

Thanks
I love this site

Russ

Russ,

Unfortunately, I know of no place that publishes that kind of information. Most mfrs regard their test and perfomance specs as proprietary.

If you are looking at aftermarket remotes, as a general rule of thumb two IR LEDs are better than one. Properly designed two-diode remotes will use one narrow and one wide angle to provide both good range and good off-axis performance. (If the transmitting diode(s) are hidden behind a plastic lens, look at the unit through the viefinder of your camcorder while pressing a button on the remote. Most CCD detectors used in camcorders can "see" into the infrared part of the spectrum, the pulsing LEDs will be quite visible.)

Bottom line though, while I don't have any direct experience with any of the Palm add-ons, I suspect that one of the ones which add CE remote control functionality to the Palm will be perfectly adequate for what you want to do. Maybe someone else on this site who has one of the add-ons will be able to comment.

Alfaman

I'm assuming the same..
thanks for helping me in the pursuit of knowledge.

Russ