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Zumo 32U4 IR LED's


#1

I purchased a couple of Zumo 32U4’s for our robotics group and we are having a ton of fun with them preparing for a sumo match. However, one deficiency we are seeing in the Zumo is that the side looking IR proximity sensors have considerably lower sensitivity to the front IR proximity sensor. Looking through the library functions, it doesn’t appear that the side IR sensors are treated any different than the front sensor in the software, so I am assuming that the surface mount LED on the sides either have lower emissivity, or a wider lens. Any chance I can get a part number for this LED? I’d love to possibly replace the surface mount one with either a more focused LED or even the same thru-hole LED’s that are in the front. The LED’s in question are D8 and D9 in the schematic.

Thanks,
Andy


#2

Hi.

The IR LEDs on the sides of the Zumo that you mentioned are wide-angle (120 degree) LEDs. There is generally a trade off between range and sensing area, and the through holes behind the side LEDs are there to allow users to play with different LEDs like you mentioned. Please share if you find some particularly effective LED arrangement!

-Claire


#3

Claire,

Other than the lensing, do you have any other specifications on the diode? Ideally, I’d like to drop in an equivalent LED with different lensing. A part number, or even typical current at nominal forward bias would probably tell me what I need.

Thanks,
Andy


#4

We do not disclose or commit to using a particular LED on those, but you can look at something like Digi-Key parts 754-1578-1-ND and VSMB10940CT-ND to get an idea. But none of that stuff you asked for really matters. You can see from the sensor datasheet that the peak sensitivity is to about 950nm, so you should get LEDs that emit around that wavelength, and beyond that, just play around with them. You can see from the schematic that the front and side LEDs are in series (except for the bit of current through the red LEDs), and the idea is to pulse the current well past any continuous ratings on the LEDs, anyway. You probably want to use through-hole LEDs so you can play with the angles and shielding more. Just getting brighter isn’t necessarily going to do that much for you unless you prevent excessive reflections from within your robot.

-Claire


#5

Claire,

Thanks again. So basically, a 20 mA nominal diode. I just don’t want to burn anything out.