here is a display grabbed from an old (90's) telephone...
http://i1.tinypic.com/n4td3b.jpg
How can i guess it's pinout ?
I think it has 12 character + 8 fixed messages on/off type (save,
redial,alarm, memo, lower , program , am, pm)
Any suggestions ?
---
From your description and the number of pins available, it would be
a multiplexed display and it would need seven pins for the [seven
segment] characters, 8 pins for the various annunciators, and 13
pins for the backplanes. It has 28 pins, so that's consistent with
your description, which is a good thing.
In order to find out what's what you'll need to find the backplanes
and then drive the segments and annunciators out of phase with their
respective backplanes, ideally with a 50% duty cycle square wave at
about 30Hz.
An easy way to do that would be to use a 7555 to get the 50% duty
cycle square wave at 30Hz, and then invert that signal to get the
out-of-phase signal you also need, like this:
+----[100k]---+------------->PHASE0
| +-------+ |
+--|TH OUT|--+----[INV]O--->PHASE1
| |___ _|
+-O|DIS R|O--+5
| +-------+
[0.22µF] 7555
|
GND
Then, connect PHASE0 to pin 1 of the display and probe the rest of
the pins with PHASE1. Eventually, one or more of the segments or
annunciators should become visible. If more than one becomes
visible, then PHASE0 is on a backplane, and you should be able to
identify all of the segments or annunciators with PHASE1. Once
you've identified the segments, you can connect one of the phases to
it and use the other phase to find the remaining backplanes by
watching the segment jump from one position to another when you
connect to the various backplanes.