Infrared data link

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Beee
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Joined: Thu Apr 03, 2003 1:01 am
Location: Ithaca, NY
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Infrared data link

Post by Beee »

I am building a fairly simple robot arm with an ultrasonic rangefinder (Daventech SRF08) at the end of the arm. I want the rangefinder to be able to spin to scan and not tangle wires. My idea is to eliminate the wires entirely and use an infrared link to transfer the TTL data. I have figured out the physical link but not the electronics. Can anyone help? I have been looking at the IrDA stuff but that seems much more involved and complicated for me to deal with. There must be tons of simple and fast circuit designs out there but I can't seem to find them. What I'm looking for is kind of like a bridge.
For my ongoing project idea look at: http://geocities.com/blovesrula/
This is oonly in the planning stage at this time. I am trying to build this by next year
I would appreciate as much help as you all can give me. Thanks, BEEE
Chris Foley
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Joined: Mon Jan 13, 2003 1:01 am
Location: Chicago IL
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Re: Infrared data link

Post by Chris Foley »

How about slip rings? That's the "classic" solution. You fashion a few rings made of spring copper or some other conductive material around the rotating shaft, and hook up wires from the rings to your electronics on the top of the shaft. Then you make pieces of spring copper which are touching and compressed against the rings, and affix them to the stationary base. These are connected to the control electronics on the base. Then, while the shaft turns, there is a constant electrical connection between the base and the rotating shaft. This sounds at first like something of a Rube Goldberg contraption, but it has been used for a century with good results. A couple of cautions, though. If you're crafty about it, you can transfer just about any signal this way from a rotating part to a stationary one. You may have trouble with electrical contact noise while the shaft is turning, especially after it's been in service for a while. Good engineering helps here. Also, you may have trouble with discontinuities if your rings have any seams. You might want transmission to occur while the shaft is stationary, and you may want to have two spring contacts for each signal and stagger the seam points on the ring so at least one spring is making good contact at any time. This may be easier and more reliable than an IR setup, and also you don't have to worry about a battery or second electrical source. Happy hunting.
Dimbulb
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Joined: Sun Oct 13, 2002 1:01 am

Re: Infrared data link

Post by Dimbulb »

The dimensional conciderations sometimes involves run-out and surface finish as performed on a lathe or seen on a dial indicator. Possibly a shaft made of a highly resistive composite casting includes brass disks (1/2" long x 3" dia), clear plexiglass (2" long x 3" dia.)and hardened hollow end shafts one side has three insulated tubes inside. The housing may be simular in design to an aluminum casting like motor alternater type with respect to the bearings. The optical ambient conciderations I will briefly describe later. The housing is retro-fitted for multiple brush and optical send and recieve assembly. <p>A purely Photo-optical coupling linking digital to the a rotary base is three part. Inside this composite shaft is a small circuit that is capable of sensing input from the end shafts and sending output through translucent disks in the composite shaft to the brush/photo-diode assembly that is stationary inside the housing. The shaft incorporates translucent disks matching dimentions to fit the brass disks. The inside of the housing needs to stay clean and free of ambient light.<p>The assembly of disks end pieces fit together by having a step cut by lathe both sides and center cut out of solid clear plexiglass and the brass has only center cut out. The hollow shaft has three cores all insulated and extend out several inches. These also are step cut and fastend to power terminal. The shaft is trued and polished.<p>If you are following this and you draw it out you may find an easier way to send light while maintaining structure during movement often times requires several proto-types to reduce size. That is relatively easy when you test it.<p>[ April 04, 2003: Message edited by: 1206DX ]</p>
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