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Robot ``Easter Egg Hunt'' discussion digest
Date: Just before September 22 1999 Date: 26 August 1999 Date: 9 July 1999 Date: 23 May 1999 Date: 18 May 1999 Date: 13 May 1999 DJ: Darrell Johnson BH: Ben Hitchcock KH: Ken Huntington SB: Steven Bolt Back to the Egg Hunt home page
The use of IR receiver modules
If no objections are received before October 20, this proposal will be copied to the Contest definition:SB> The Playground will be in an ordinary room, lit by ordinary SB> natural or artificial light. Since the IR beacon is modulated, SB> it should be easy to make sure that your Egg Hunter is not SB> confused by mains modulated artificial light. But eye-challenged SB> Egg Hunters may be offered a run in diffuse daylight on request. SB> And to guarantee good beacon reception, Hunters may also ask for SB> any modulated IR emitters (like IrDA and remote control devices) SB> to be switched off. /PRE>
SB> My own Egg Hunter (Jaws) SB> ignores remote control devices and such, because they operate on SB> a much higher frequency than his 4.5KHz.SB> In earlier robot discussions, the use of those handy little IR SB> receiver modules has often come up. For reasons that will soon SB> be clear, I'm not too fond of them. But I'm currently working SB> on a little commercial project which needs a kind of IR SB> `radar'. As the available pcb area is just about zero, there SB> was no alternative. SB> As you can see in the attached diagram, component count is low. SB> The SFH506-30 (30KHz) receiver module also uses very little SB> power (less than 1mA). It is extremely sensitive; a hand at SB> 40cm distance from the emitter/receiver is easily `seen', SB> despite the 680 ohms current limiting resistor on the SFH484. SB> It does however require a 4-cell battery. SB> A more serious drawback is the fact that it shares its SB> frequency band with the large and increasing number of remote SB> control devices in the average household. I developed a few SB> lines of software which make certain that my `radar' doesn't SB> react to these other IR emitters - it even manages to get a SB> fair number of good range pulses out despite being illuminated SB> by a remote control with a stuck key. But such `jamming' is SB> effective enough to seriously reduce the number of range SB> pulses. SB> Is all this relevant to Egg Hunting? SB> It may well be if you want such reveiver modules on your Egg SB> Hunting `bot, to navigate using an IR beacon. My simple filter SB> method works because it controlls the emitter timing. A filter SB> which has to deal with just the received signals faces a much SB> harder task. SB> Imho these receiver modules do not allow you to achieve easy SB> and accurate navigation in the presence of active remote SB> control devices. The simple remedy is to use a special SB> receiver. Jaws' eyes operate on about 4.5KHz; he doesn't even SB> notice my various remote controlls. Moreover, he is able to SB> receive continuous wave signals, which makes it very easy to SB> lock on his beacon (the SFH506 demands pulses, and gives output SB> after a pulse ends). And of course Jaws' receiver works fine on SB> a 3-cell battery. SB> But I can imagine that many Egg Hunters would prefer to use SB> receiver modules anyway. So it may be wise to introduce an SB> environmental rule, prohibiting the use of IR remote control SB> devices in the contest room. How do you all feel about that? SB> One other matter: I selected the SFH484 as IR emitter because SB> of its narrow (16 degrees) beam width. Of course that makes it SB> less appropriate for a Playground beacon, which needs to SB> illuminate 90 degrees. The SFH485 looks identical to the 484, SB> but has a 40 degree beam. A couple of those might make a nice SB> beacon, perhaps aided by a narrow beam emitter to create more SB> or less equal (and just enough) intensity everywhere on the SB> Playground. Too much light increases the risk of unwanted SB> reflections. SB> Finally, if you'd like a closer look at my SFH506 application SB> software, a self-extracting package with all relevant files is SB> here.Ben Hitchcock and Ken Huntington replied:BH> Funny how things happen all at once... BH> Last night I wrote an e-mail to the group explaining my BH> progress with my IR Radar. I was almost finished, and was just BH> touching up the photo of my IR sensor when my computer crashed. BH> I had to go, so I didn't send it until now. BH> And when I open my e-mail today, what do I see but Steven BH> explaining my conundrum exactly! BH> Anyway, here's the gist of my previous (lost) message: BH> I have improved my IR radar considerably. I now have a range BH> of 7 cm for easter eggs, and a blank sheet of white paper (or BH> my hand) sets off the receiver at a distance of 0.5 cm. This BH> is acceptable, as far as I'm concerned. BH> The circuit is quite 'BEAMish' in design. I have two IR LEDs, BH> pointing the same direction, one on each side of a U-60 IR BH> receiver module. The LEDs flash alternately at 38 kHz, which BH> just so happens to be the same frequency that the IR receiver BH> module works at. Because an Easter Egg has variable BH> reflectivity, it will reflect one LED better than the other - BH> so the receiver will see a net 38 kHz signal. But if a wall or BH> other matt object is present, then both LEDs will reflect BH> equally back to the receiver, so it won't 'see' anything. BH> I'm happy with the results at the moment. I improved the BH> circuit by using different IR diodes, and by shrouding the BH> receiver. KH> Beamish? I don't know but it is seriously clever. I don't know KH> if it will work under all playground conditions so Ameba still KH> has hope :) BH> The attached jpeg is of the old setup, the new setup looks the BH> same, except that the IR diodes are further apart, and the BH> receiver has a black shroud. The new setup hasn't come off BH> the breadboard yet. It remains to be seen how well this system BH> works when actually attached to psyclone! KH> Keep it coming.I think it's great that serious work on a long range sensor is being done for the first generation of Egg Hunters. If it works, Ben's chances of winning the contest are much increased! Ameba and Jaws both rely on touch alone, so they are bound to miss a few Eggs, and/or take excessively long to find some of them. But we're keeping up our hopes. In fact, Jaws is nearly ready to start hunting...
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