Re: Red LED HPs Message #2 Posted by Michael Meyer on 2 Jan 2004, 12:11 a.m., in response to message #1 by Trent Moseley
Trent,
There are many factors that determine the brightness of the LED display. Each display is a different kind: The HP-67 has (as I recall) 3 LED modules with 5 digits each soldered like chips on the circuit board. The HP-25C has a module that fits over pins, and the 31E is similar, but has pins soldered to the module, and it slides into the circuit assembly. All have magnifying lenses.
The light output is dependent on the size of the LED and how it is magnified, the darkness of the red filter lenses, the rate of "scanning" (only one digit is "lit" at a time), the lumen rating of the LED (usually expressed in micro-candle power), and many other factors. The method to adjust some resistors on the HP-67 to change the brightness is posted on old threads on this Forum. I'm sure the same can be done with the HP-25C, though with the way the 31E is made, it would seem difficult to change the display brightness.
My brightest LED calculator by far is an old TI SR-50A. Those LED's are REALLY bright.
Hope this helps.
Michael
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