Long range IR signal

[Richard Hosking]

I am trying to make an IR (as in TV remore control) based gun game
Commercial ones seem to have a range of about 100m, with reasonably
tight focussing.
I have tried a conventional IR diode with a tube to limit the field.
This was receiveable over about 20m with good focus.
The receiver is a module with a photodiode/amp/AGC/BPF and logic. The
centre freq is 38KHz modulated to get rid of extraneous light sources.

Cheap optics dont seem to improve things much.
How do they achieve this sort of range?

I would be grateful for pointers

Thanks
Richard

 

[John Woodgate]

I read in sci.electronics.design that Richard Hosking
<richardh@iinet.net.au> wrote (in
<425912d7$0$8392$5a62ac22@per-qv1-newsreader-01.iinet.net.au&gt about
'Long range IR signal', on Sun, 10 Apr 2005:

I am trying to make an IR (as in TV remore control) based gun game
Commercial ones seem to have a range of about 100m, with reasonably
tight focussing.
I have tried a conventional IR diode with a tube to limit the field.
This was receiveable over about 20m with good focus.
The receiver is a module with a photodiode/amp/AGC/BPF and logic. The
centre freq is 38KHz modulated to get rid of extraneous light sources.

Cheap optics dont seem to improve things much.
How do they achieve this sort of range?

Parabolic reflectors at each end, very carefully adjusted for best
parallel beam.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Ian Stirling]

Richard Hosking <richardh@iinet.net.au> wrote:

I am trying to make an IR (as in TV remore control) based gun game
Commercial ones seem to have a range of about 100m, with reasonably
tight focussing.

What size of light source are you using?
You want the smallest possible light source you can.

Alternatively, have you considered laser diodes?
Take a 1mW laser pointer, add a diverging lens in order to make the
spot size ~1m, and modulate it.

 

[Fritz Schlunder]

"Richard Hosking" <richardh@iinet.net.au> wrote in message
news:425912d7$0$8392$5a62ac22@per-qv1-newsreader-01.iinet.net.au...

I am trying to make an IR (as in TV remore control) based gun game
Commercial ones seem to have a range of about 100m, with reasonably
tight focussing.
I have tried a conventional IR diode with a tube to limit the field.
This was receiveable over about 20m with good focus.
The receiver is a module with a photodiode/amp/AGC/BPF and logic. The
centre freq is 38KHz modulated to get rid of extraneous light sources.

Cheap optics dont seem to improve things much.
How do they achieve this sort of range?

I would be grateful for pointers

Thanks
Richard

Well I don't know how other people do this sort of thing, but if it were me
I would place a TSOP1238 receiver by Vishay (available from Mouser) on the
target, and then mount one or more SFH4503 infrared LEDs (available from
Digikey) by OSRAM on the gun inside of a non-internally IR reflecting
barrel. I would try to shade the TSOP1238 from direct sunlight, but I would
not worry about any kind of special optics.

Datasheets for the parts here:

http://www.vishay.com/docs/82013/82013.pdf

http://www.osram.convergy.de/upload/documents/2003/12/10/11/58/sfh4501.pdf

The TSOP1238 is the most sensitive/robust/well documented/readily available
receiver I am currently aware of. The SFH4503 is the most powerful/small
beam angle/readily available LED that I am aware of that is suitable for
this application.

The TSOP1238 expects the incoming light to be modulated at 38kHz, but it
also expects to see pulse packets of 10+ cycles (though not too many) for
maximum reception strength. I would use a 10 cycle packet (IE: 38kHz
carrier at 50% duty cycle, but only produce 10 complete cycles of that
carrier for each trigger pull, assuming a "semi-automatic weapon"). If you
make sure the duty cycle is kept very small (<1% overall), then it should be
allowable to pulse the IR LED with high current in the range of 1.5A to 2A
during each ten cycle packet. You will probably need some large low ESR
capacitors to provide that pulse energy, depending upon your power source
and the wiring impedance.

The datasheet is a bit sketchy about LED output at 1.5-2A, but something
maybe around 300mW typical (but much worse for low yielding LEDs) of total
radiant IR might be reasonable. Given the half power beam angle of +/-4
degrees, by my calculations at 100 meters it may be possible to achieve
something better than 1mW/m^2. Someone double check my math on this, I may
have made some error(s).

Figure 6 of the TSOP1238 datasheet leads me to believe that this irradiance
may be enough to function under direct sunlight at 100 meters. I of course
haven't experimentally verified this to be the case, but I think optimism is
justifiable. Range would be much better at night time.

 

[Fritz Schlunder]

"Fritz Schlunder" <me@privacy.net> wrote in message
news:d3bjs9$8n6$1@domitilla.aioe.org...

Figure 6 of the TSOP1238 datasheet 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...

 

[Richard Hosking]

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@privacy.net> wrote in message
news:d3bjs9$8n6$1@domitilla.aioe.org...


Figure 6 of the TSOP1238 datasheet 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...

 

[Fritz Schlunder]

"Richard Hosking" <richardh@iinet.net.au> wrote in message
news:425bc4a7$0$20399$5a62ac22@per-qv1-newsreader-01.iinet.net.au...

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.

The carrier frequency (in this case 38kHz) should always be about 50% duty
cycle. Assuming you are using a standard receiver IC, then you will not
likely get any benefit from shrinking the carrier frequency duty cycle. In
fact you may end up with less sensitivity even if you are pulsing the LED(s)
with more current.

Normal receiver ICs expect the carrier to be modulated on and off at some
lower frequency. If you continuously run the LEDs at 38kHz the receiver IC
will eventually lose sensitivity. 38kHz is around the frequency of some
compact fluorescent lamps, so they could easily interefere with your signal
if the receiver IC was sensitive to continuous 38kHz. So instead devices
like the TSOP1238 have automatic gain control elements that reduce
sensitivity if the detected 38kHz light modulation is continuous (like it
would be from fluorescent lamps).

Instead the data needs to be encoded somehow to avoid continuous
transmission. The TSOP1238 datasheet suggests that the 38kHz carrier should
be turned on for a minimum of ten 38kHz (50% duty cycle) cycles up to a
maximum of seventy cycles. After that no signal should be transmitted for
at least fourteen cycles of the carrier frequency before another pulse
packet it sent.

Since by the sounds of your situation you don't need complicated data
transfer, I suggest using ten or eleven cycle bursts of 38kHz @ 50% Duty to
minimize LED stress and power consumption. A possible implementation might
be something like follows: Have a free running continuous 38kHz +/-2%
frequency tolerance 50% duty cycle oscillator. Have a switch debounce
circuit for the trigger switch with the output feeding a one shot. The
output of the one shot is programmed to last about ten (or better eleven)
38kHz cycles or in other words about 290us. Have the output of the one shot
AND gated with the 38kHz 50% duty cycle oscillator. The output of the AND
gate drives the LED (through suitable high current LED driver).

The net result is under normal operation the LED is not driven at all. Then
when someone presses the trigger you get one set of ten or eleven LED pulses
each lasting about 13us (with 13us gaps in between), and nothing else after
that (until the trigger is manually pressed again).

This is the basic idea, but feel free to modify it to suit your needs
better.

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?

I don't understand your description of your constant current source, so I
can't make comments as to its feasibility, but using a constant current
source for driving the LED seems rather more complicated than needed.
Assuming you have a regulated supply voltage (5V or more would be nice),
what is wrong with using a simple resistor to limit the current?

What is your power supply (batteries? regulated? voltage? current
capability?)? An eleven pulse packet consisting of eleven 13us 1A pulses
requires 143 microcoulombs of charge (Q=I*t). If this is delivered entirely
from a capacitor, then you can approximate the voltage droop for various
capacitances using the formula Q=CV. For example if we allow a 250mV sag
when drawing 143 microcoulombs, then we need 0.000143 = C * 0.25, so a
capacitance C of 572uF. The ESR should be low enough that the output
voltage of the capacitor doesn't sag unreasonably at 1A peak current. If
you use a resistor to limit the current then you can simply make it smaller
to compensate for whatever ESR the capacitor has to enable 1A peak current
pulses. None of this is too precise, but neither does the LED need precise
current levels. Any standard 470uF or 680uF capacitor or so from 5V should
function quite nicely. If the power supply is particularly stiff and easily
able to cope with fast 1A+ pulses with minimal droop, then no extra
capacitance is strictly required (though a small amount may still be desired
for minimizing inductance based overvoltage effects).

Thanks for any ideas
Richard