LED in HP 82104A



#2

Hello!

Do you know some things about the funktion of the LED in the HP 41 card reader?

Best regards.

Gunnar


#3

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.


#4

Hi!

I´m 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

#5

Hi,

I don't know exactly, but I think it's some kind of light barrier ('Lichtschranke')

Regards,

Raymond

#6

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


#7

I think, that the "sense" is a electrical contact. I don´t see a photodiode or something else. Only a stand alone LED (no colour).

Gunnar

#8

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.

#9

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.

#10

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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