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Robot ``Easter Egg Hunt'' discussion digest
Previous discussion page Next discussion page Date: 26 Aug 1999 DJ: Darrell Johnson BH: Ben Hitchcock KH: Ken Huntington SB: Steven Bolt Back to the Egg Hunt home page
IR black/white floor detection
If no objections are received before September 20, this proposal will be copied to the Contest definition:SB> Gathering area: matt black surface. Paint or paper ensuring SB> maximum contrast with the matt white Playground floor, to SB> normal and IR-sensitive eyes. SB> Always this size (radius 20cm) and in a corner. The border of SB> this area is also painted matt black. SB> SB> For a contest, the gathering corner will thus be required to show SB> contrast in IR light, as checked using Ken's method: KH> A generic IR photo-transistor was used with a 22K collector load; KH> the IR source, a 60W incandescent bulb about 50cm above the KH> surface(s) to be tested. Using a 5V power supply, with the KH> photo-transistor masked to permit light to enter only through the KH> lens of the device, point it at the surface at about 60deg at 1 KH> to 2cm above it. The collector voltage should read 3V or better KH> while pointed at a low reflective surface and 0.2V or less with a KH> high reflective surface and about 4.5V with the light turned off. KH> It seems pretty rinky dinky but works well.
The procedure is indeed not critical, and neither are the materials:SB> I tried it using the detector-half of a CNY37 IR optocoupler SB> (open type, intended to see the passing of a vane between emitter SB> and detector), with a 22K bias. The results obtained fit Ken's SB> values; my low and high reflective surfaces were ordinary black and SB> white paper. KH> I have a feeling that two coats of any matt black paint would do KH> the job quite nicely. SB> So do I, and at least some black papers appear to be equally SB> acceptable.
So why bother bringing up this point? Well, An IR emitter and detector in the middle of a Hunter's underside allows very simple circuitry (like just two resistors) to give a clean one/zero output, so the `bot has no difficulty knowing whether it's on the white Playground floor or in the black gathering area. I originally thought that all matt whites and blacks would be just about equally visible to normal and infrared `eyes', but Ken discovered that aint so:KH> I may have run into a problem concerning the definition of the KH> gathering area KH> Gathering area: matt black surface (piece of black paper). Always KH> this size (radius 20cm) and in a corner. The border of this area KH> is also matt black. KH> At first glance, it all looks good but I had a problem when KH> building the commutators for Ameba. I tried to use a pattern that KH> I printed. It looked beautiful but the black ink is invisible to KH> the Infrared TXRX assembly and I ended up having to paint my KH> wheels matt black using modeling spray paint and applying the KH> pattern by hand. My problem and possibly yours is that I use the KH> same type of IR TXRX device to detect the gathering area and KH> while my playground will be no problem as I will be using the KH> same paint, there is no guarantee that the same will be true for KH> any other playground. KH> Although I could replace my current circuit with another using a KH> red LED and photo detector, the IR circuits are most common, come KH> in 99 flavours and are dirt cheap. (especially if you can find KH> them your bit bucket :) SB> Your arguments in favour of facilitating IR black/white floor SB> detection are fair enough, imho. Just one question: SB> SB> Black paper doesn't equal black ink. Are we sure that an IR SB> optocoupler has difficulty seeing the difference between matt white SB> wood and ordinary matt black paper? SB> SB> I admit that I didn't actually try to confirm that - should have, SB> sorry. (Jaws is supposed to use a simple form of distance SB> measurement relative to the IR beacon, to determine whether he's in SB> the corner.) KH> I've now done some investigation and found: KH> Canon bubble jet printer invisible to IR. KH> Black construction paper invisible to IR. KH> Laser printer toner visible to IR. KH> Data books printing visible to IR. KH> Model paint visible to IR. KH> It's not a big list and it may not be true for every laser KH> printer, model paint or construction paper. SB> To make this a practical part of the standard Playground, we need SB> to specify either the black surface treatment, or a standard test.
At this point, Ken came up with his test involving a generic IR photo-transistor. As determining IR contrast is easy enough, a contest organizer will be required to `qualify' the matt black of the contest Playground in this way, if doubts arise - and assuming no one objects to this demand before September 20. Ben commented:BH> I am planning to use the visible spectrum to determine where my BH> bot is. A simple LDR should do the job nicely, I think. I have BH> no objections to making the corner dark to IR, so long as it is BH> still reasonably black to human viewers.
Which it will be; as black as matt black can be :)
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