Woodstock Display Problem

[teenix]

(02-14-2020 11:58 AM)cjmcc Wrote:  I've attached a photo of the display showing 908172635.4

Going left to right, you can see the decimal point is ambiguous - several look possibly lit.
The 9, 0, 8, and 1 are reasonable, but the 7 has an extra segment 'almost' lit, as do the 2, (6 looks OK because that segment is supposed to be lit), 3 and 5 (which look like a 9 and a 6).


For reference, the on-line emulator HP29u gives a much cleaner look.

Only 1 LED segment is lit at any one time and are excited in order a b c d e f g h etc

It looks like segment b is lighting along with segment f, ie the 7 and 2 digits.

As Bob mentioned the only real way to check the problem is with a scope. You could then see the signals that are exciting the display with and without the display connected.

Check the [strobe] pins on the anode and cathode drivers. If that signal is "fuzzy" it might explain the ghosting.

cheers

Tony