Choosing an emitter for micromouse sensors

By | December 17, 2011

Most commonly, micromouse reflective sensors use Infra Red LEDs as the emitter component. That is all very well and suits many, or most, phototransistors. the thing is, you cannot easily see where they are pointing and what kind of illumination they are providing. Here is a sample of 13 different emitters…
Each emitter is mounted 100mm away from a piece of paper overprinted in black by a laser printer. The black surface absorbs most of the light falling on it but reflects enough so that a modified webcam can see the pattern of illumination. In the following tests, each emitter is supplied from a 5V supply through a 330 Ohm current limiting resistor. No attempt was made to put a constant or predefined current through them. It may have been better to supply each form a 100mA constant current supply. Feel free to repeat the trial that way.

There were 11 Infra Red and 2 visible light LEDs tested. The spot size is the diameter of the 50% power circle at 100mm based on the published datasheet:

Part number 1/2 angle mW/Sr I (A) nm Spot Size
SFH4550-DW 3 400 0.10 850 5
OSI3NA5111A 7.5 60 0.10 850 13
SFH484-2 8 80 0.10 880 14
SFH4580 15 25 0.10 880 26
OPE5594A 10 80 0.10 940 17
TSAL5100 10 130 0.10 940 17
TSAL6100 10 130 0.10 940 17
SFH4511 4 63 0.10 950 7
SFH4503 4 63 0.10 950 7
GL514 7 950 12
SFH409 20 6.3 0.10 950 34
Part number 1/2 angle mcd I (A) nm Spot Size
TLSH180P 6 10000 0.02 623 10
HLMPEG08 6 5000 0.02 626 10

 

There is little doubt that, so long as you have a suitable detector, the SFH4550 puts out a wonderful small, bright beam. This is generally a good thing but when running down a diagonal, the beam can be so tight that you fail to see obstacles that are not directly in the path of the mouse.

The spot produced by the OSI3NA5111A seems much brighter than the datasheet figured for radiant intensity would suggest.

The SFH4511 and SFH484 both have strong annular rings which can give confusing readings when the walls are at an angle to the detector.

Although the datasheets of the TSAL5100 and TSL6100 are all but identical, it would appear that the TSL6100 beam is a little more diffuse. That could, of course, just be the sample I used.

The datasheet gives the half-angle for the OPE5594E as 20 degrees but that seems to actually be the included angle. To be consistent with other datasheets, the half angle should probably be quoted as 10 degrees.

If your detector is more sensitive at 850nm, the emitter of choice seems to be either the SFH4550 or the OSI3NA5111A. While, for 950nm detectors, the best choice is probably one of the OPE5594E, TSAL6100 or TSAL5100 with the OPE5594E having a better defined spot.

Both the red LEDs have nice spot patterns and would do very nicely for a visible light sensor. The TSLH180P is rather more efficient though.

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