Re: Long range IR signal

Thanks for this
At present I have a current source (PNP transistor) from + supply to diode to FET logic level switch to ground. Assuming I wanted a 1A pulse to the diode at about 5-10% duty cycle at 38 KHz, this would mean a 1-2 usec pulse. I presume you would have to use a fairly fast RF transistor with a suitable current rating as the current source with a low ESR capacitor (say ?4700uF) across the supply close to the circuit. The FET swich should handle the situation OK. I would use the PNP current source with emitter resistor of 0.6 ohm and two diodes to base from + supply - would this work or is there a better solution?
What devices would be suitable for this, and what other considerations?

Thanks for any ideas
Richard


Fritz Schlunder wrote: 
"Fritz Schlunder" <me@xxxxxxxxxxx> wrote in message
news:d3bjs9$8n6$1@xxxxxxxxxxxxxxxxxxxxx


Figure 6 of the TSOP1238 data*** leads me to believe that this 

irradiance

may be enough to function under direct sunlight at 100 meters. 


Hmm...  Maybe better modify that.  Figure 6 indicates 5900K sunlight at a
level of 8200 lux is roughly an irradiance of 10W/m^2 (at the wavelength of
interest).  But if you look at this site here on section 10 (How bright are
natural light sources):

http://www.stjarnhimlen.se/comp/radfaq.html

It would have you believe direct sunlight is 130,000 lux.  Since the
TSOP1238 quickly loses functionality past 10W/m^2 and becomes worthless at

30W/m^2, then it probably won't work at all under direct sunlight no matter 

the range.  The link suggest full daylight (not direct) is from 10k lux to
25k lux, so maybe it can still work provided the receiver is well shaded
from sunlight.  Perhaps if the receiver was mounted in its own
non-internally IR reflecting barrel...


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