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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
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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.


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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