I purchased a bunch of the Sharp (are they really?) branded GP2Y0A21 IR sensors via aliexpress. This is my first time purchasing from alibaba. I’ve purchased lots of stuff through ebay; most of it comes from Hong Kong.
Sharp IR sensors typically cost in the $12 to $16 range. I ordered several from China at $6.50/unit. I tested each one to make sure each was worked as was within specification. I plotted (sorry not going to publish) the returned values. I am surprised how close each sensor was to the average. I’m thinking the amount of jitter in the readings may be from dust in the air.