HP Forum Archive 09

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LED in HP 82104A Message #1 Posted by Gunnar on 3 Dec 2002, 4:01 p.m. Hello! Do you know some things about the funktion of the LED in the HP 41 card reader? Best regards. Gunnar

Re: LED in HP 82104A Message #2 Posted by Vieira, Luiz C. (Brazil) on 3 Dec 2002, 4:14 p.m., in response to message #1 by Gunnar Hi; I have one working card reader and I have seen at least 15 of them. I have never seen a LED in any. I'm somewhat curious; does it work alright? What is the possibility it's not a card reader inside? I read in this forum that a sort of MLDL was built inside a card-reader's box. Anybody know anything about it? Is it possible that you have an MLDL (machine-language development l...(?)) instead of a card-reader? If it is indeed a card reader AND if you, one day, open it, please, take pictures so we can figure out what is this LED for./ Cheers.

Re: LED in HP 82104A Message #3 Posted by Gunnar on 3 Dec 2002, 4:48 p.m., in response to message #2 by Vieira, Luiz C. (Brazil) Hi! Iīm sure that it is a LED, but i have never seen it lighting (IR ?). I have an normaly card reader (I hope). Best regards Gunnar

Re: LED in HP 82104A Message #4 Posted by Raymond Hellstern (Germany) on 3 Dec 2002, 4:16 p.m., in response to message #1 by Gunnar Hi, I don't know exactly, but I think it's some kind of light barrier ('Lichtschranke') Regards, Raymond

Re: LED in HP 82104A Message #5 Posted by Michel Beaulieu on 3 Dec 2002, 4:53 p.m., in response to message #1 by Gunnar I think it a IR LED that, with a receptor, "sense" the presence or the card insted or a dip switch activate with the card

Re: LED in HP 82104A Message #6 Posted by Gunnar on 3 Dec 2002, 5:13 p.m., in response to message #5 by Michel Beaulieu I think, that the "sense" is a electrical contact. I donīt see a photodiode or something else. Only a stand alone LED (no colour). Gunnar

Re: LED in HP 82104A Message #7 Posted by Gunnar on 3 Dec 2002, 5:13 p.m., in response to message #5 by Michel Beaulieu I think, that the "sense" is a electrical contact. I donīt see a photodiode or something else. Only a stand alone LED (no colour). Gunnar

Re: LED in HP 82104A Message #8 Posted by David Smith on 3 Dec 2002, 5:16 p.m., in response to message #1 by Gunnar It is an IR led used to detect when the card edge has passed by. I've never had to figure out if it is for start-of-card, end-of-card, or write-protect. There is a tiny photodiode mounted on the little circuit board that forms the switch contacts. The card passes between the LED and the photodiode.

Re: LED in HP 82104A Message #9 Posted by Tony Duell (UK) on 3 Dec 2002, 5:38 p.m., in response to message #1 by Gunnar There is a photodiode (or maybe a phototransistor) on the switch contact PCB on top of the reader mechanism. This LED (which is an IR one, so you won't see it glow) forms a light barrier with that detector to sense the clipped corner of the card fro wrtie protect. Somewhat suprisingly, the card-inserted and card-at-head functions are still performed by mechanical switches. The LED is driven by the 1826-0322 sense amplifier chip -- the part of that chip that was used for motor control in (e.g.) the HP67.

Re: LED in HP 82104A Message #10 Posted by Vieira, Luiz C. (Brazil) on 3 Dec 2002, 11:54 p.m., in response to message #1 by Gunnar Hi, Gunnar. I understood the LED was outside the card reader, as you did not mention your card reader was openned. I gave my thoughts wings and they have gone far, far away... Indeed, the card reader has an inner tinny light-sensytive device. Sorry for the bad clues... Cheers.

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