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Woodstock's LED display characteristics
Message #1 Posted by Vieira, Luiz C. (Brazil) on 26 Nov 2002, 9:50 p.m.


does anybody have the electrical characteristics for the LED's that compose the digit's segments for the Wodstocks displays? Are they regular LED's?

I'd like to know also the driver's operating output values (hand-scratched waveform with peak and time values are welcome, sure!), if available.

I do not have an oscilloscope that I could use for this sort of measurement (mine is a vacuum-tube scopelab without scale patterns... Please, don't laugh too loud!), so I'm asking for any information you have.

What for? I'll let you know soon... No bad stuff, believe me.

Thank you for any info.


Re: Woodstock's LED display characteristics
Message #2 Posted by Andrés C. Rodríguez (Argentina) on 28 Nov 2002, 7:18 a.m.,
in response to message #1 by Vieira, Luiz C. (Brazil)

Luiz: I think I have just some hints for your question.

Almost sure, the displays are common cathode (one cathode per digit), the maximum direct (permanent) current should be 15 to 20mA per segment.

The display is multiplexed and scanned by firmware routines; if you take a look at the HP45 emulator and related patents documentation, which includes some of the code, you will have a reference about software-refreshed displays. By the way, if a hardware segment decoder (like the TTL 7448) had been used, messages like "Error" or "OF" would have not been possible.

Asuming a 1/12 duty cycle (only one digit is turned on at any time); or eventually a 1/8 duty cycle (one segment active at a time), you may obtain a peak current value which will be averaged in time. However, I think it is safe not to exceed 40 or 50 mA for pulsed operation, as this case is.

Please take these just as not confirmed suggestions...

By the way, my trip to Brazil was suspended...

Re: Woodstock's LED display characteristics
Message #3 Posted by Vieira, Luiz C. (Brazil) on 28 Nov 2002, 12:01 p.m.,
in response to message #2 by Andrés C. Rodríguez (Argentina)

Hi, Andrés;

too bad you're not giving our Country the pleasure (and merit) to have you here. Hope you have other chances to come.

About the LED's: have you noticed that each segment of each digit is built with 4 (sometimes five) lit dots? Say, if you use a magnifying lens you'll see there are dots, not a line, for each segment.

Is it just a mask for better reading? Is each segment built with only one semiconductor? This fact is the one that lead me to ask about the displays. Even the HP97 uses these constructive blocks, having a different set of magnifying lenses.

Have anyone tried to find replacement for these displays? (I'm trying to find any)

Thank you very much.


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