One of the open questions about using the Wii Remote's infrared-sensitive camera has been which part of the infrared spectrum it was most sensitive to. Our plan to track retroreflective strips on the course will work best if we flood the scene with IR illumination in the right range.
There is no official word on the subject from Nintendo, but there is anecdotal evidence that the optimal wavelength is 940 nm.
I have tested IR illuminators at five different fixed wavelengths: 850, 870, 890, 940, and 950 nm. My results agree with those above - the Remote's camera seems to be most sensitive to illumination at 940 nm.
1 comment:
notes from the test:
WiiCane project
IR illuminator comparison notes
3/6/09
Need to do a quick evaluation of the Wii Remote's IR-sensitive camera's response to different IR wavelengths. The Remote's IR filter and the nature of its camera mean that there is an optimal wavelength of IR light for the Remote's computer vision system. Anectdotal evidence suggests that the ideal wavelength is around 940 nm ( http://www.wiimoteproject.com/ir-pens/what-is-the-wiimote%27s-preferred-peak-wavelength/ )
Five LEDs to evaluate - they have approximately equal radiant intensity spread across 5 wavelengths: 850, 870, 890, 940, and 950 nm
#1
Osram Opto Semiconductors part SFH4550
Digikey part 475-1200-ND
850 nm emitter in a 5 mm package
wavelength = 850 nm
forward voltage = 1.5 V
DC forward current = 100 mA
viewing angle = 6 degrees
radiant intensity = 400 mW at 100 mA
$0.60 single unit price
#2
Vishay Semiconductor part TSFF5210
Digikey part 751-1207-ND
high-efficiency 870 nm emitter in a 5 mm package
wavelength = 870 nm
forward voltage = 1.5 V
DC forward current = 100 mA
viewing angle = 20 degrees
radiant intensity = 90 mW @ 100 mA
$1.08 single unit price
#3
Vishay Semiconductor part TSHF5210
Digikey part 751-1210-ND
high-speed 890 nm emitter in a 5 mm package
wavelength = 890 nm
forward voltage = 1.6 V
DC forward current = 100 mA
viewing angle = 20 degrees
radiant intensity = 68 mW @ 100 mA
$0.76 single unit price
#4
Vishay Semiconductor part TSAL6100
Digikey part 751-1203-ND
high-efficiency 940 nm emitter in a 5 mm package
wavelength = 940 nm
forward voltage = 1.35 V
DC forward current = 100 mA
viewing angle = 20 degrees
radiant intensity = 80 mW @ 100 mA
$0.59 single unit price
#5
Osram Opto Semiconductors part SFH 4511
Digikey part 475-1461-ND
950 nm emitter in a 5 mm package
wavelength = 950 nm
forward voltage = 1.3 V
DC forward current = 100 mA
viewing angle = 8 degrees
radiant intensity = 63 mW @ 100 mA
$0.46 single unit price
test setup:
All can handle If = 100 mA, Vf ranges from 1.3 V to 1.6 V. Using simple current-limiting resistor and a 5 V source:
#1 R = (5 V - 1.5 V) / 0.1 A = 35 ohm (0.35 W)
#2 R = (5 V - 1.5 V) / 0.1 A = 35 ohm (0.35 W)
#3 R = (5 V - 1.6 V) / 0.1 A = 34 ohm (0.34 W)
#4 R = (5 V - 1.35 V) / 0.1 A = 36.5 ohm (0.365 W)
#5 R = (5 V - 1.3 V) / 0.1 A = 37 ohm (0.37 W)
For this quick, subjective comparison, I'm standardizing on one setup: a nominal 49.9 ohm, 1%, 0.4 W metal film resistor in series with each of the LEDs under test, all powered from a 5 V supply.
The LED under test is situated precisely 20" from the front of the Wii Remote and the LED is adjusted until the maximum "size" reading is achieved in Darwiin Remote's IR Info window. The maximum size is then recorded and used as the LED's score.
results:
The Remote responded to all wavelengths. The scores were:
#1 - 850 nm - size: 2
#2 - 870 nm - size: 2
#3 - 890 nm - size: 3
#4 - 940 nm - size: 4
#5 - 950 nm - size: 3
Maximum sensitivity does seem to be right at 940 nm
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