Robotics : 4585


Robotics / 4585	4584 \| 4586

Subject:	Re: Using the IR Port to simultaneously send and receive for proximity sensing
Newsgroups:	lugnet.robotics
Date:	Fri, 16 Apr 1999 07:23:13 GMT
Original-From:	Peter Hesketh <pbh@phesk.=StopSpam=demon.co.uk>
Viewed:	1029 times

In article <01BE8785.9B90A2A0.david.cuthill@home.com>, David Cuthill <david.cuthill@home.com> writes > I haven't really looked into this but can the IR port on the RCX be used to > send out a message and then flip to receive the reflected infrared light > thereby using it as a sensor and still have 3 ports left for other sensors? Unfortunately the speed of light is *** to fast. A reflection from an object 2 feet away would return in 4 nanoseconds. Each data bit of the transmission takes an enormous 417 microseconds, so the reflection is delayed by one hundred thousandth of a bit time. As even the shortest message contains 77 bits, the message length is 7,700,000 times longer than the delay time. In other words, the reflection comes back near as dammit instantaneously, and is added to the reflections inside the IR module which swamp it. After the last bit of the message has been sent, all is quiet because the reflection has finished. -- Regards - Peter Hesketh, Mynyddbach, Mon. Forty reasons why a dog is better than a woman: number 39 "Dogs aren't catty." -- Did you check the web site first?: http://www.crynwr.com/lego-robotics

Message has 2 Replies:

		Re: Using the IR Port to simultaneously send and receive for proximity sensing
(...) In fact, the IR emitters and IR receiver are in such close proximity that the receiver already receives whatever the emitters emit, using a direct path. The RCX ROM ignores messages it sends out and is thereby able to avoid getting lost in the (...) (25 years ago, 16-Apr-99, to lugnet.robotics)

		Re: Using the IR Port to simultaneously send and receive for proximity sensing
(...) Ah, this is a vital piece of information I had hitherto missed. I had been puzzling over the 30ms delay which makes the Mark R. David proximity detector work, 77 times 417us is 32ms - Mark is sampling right at the end of the transmission. My (...) (25 years ago, 16-Apr-99, to lugnet.robotics)

Message is in Reply To:

		Using the IR Port to simultaneously send and receive for proximity sensing
I haven't really looked into this but can the IR port on the RCX be used to send out a message and then flip to receive the reflected infrared light thereby using it as a sensor and still have 3 ports left for other sensors? I have read about using (...) (25 years ago, 16-Apr-99, to lugnet.robotics)

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