trying to use AT&T VFD display module
ethan.dicks at gmail.com
Tue Dec 9 23:51:04 CST 2008
On 12/6/08, Jeff Jonas <jeffj at panix.com> wrote:
> I salvaged several AT&T/Lucent/Avaya
> D401A Digital Display Modules,
> apparently from a Definity phone system.
> The label says
> D401A AT&T
> 89338 series 1
> The module has 8 touch-buttons and LEDS
> and an Itron DC 405A2 VFD
> (one line of 40 characters,
> each char a 5x7 matrix)
> I'd like to use the entire module
> since it has a microcontroller and power supply,
> but I have no clue as to the interface.
> Any help would be appreciated, starting with pinout.
> I really need the internal programming document
> with all the commands :-(
I don't have any information on that particular device, but I have
fiddled with a number of text-and-button frontpanels over the years.
Does that Itron VFD look like it is "formatted" or bare? A formatted
VFD would typically have a PCB the same size or smaller permanently
affixed to the back of the glass, and that PCB would have a small
number of SMT chips on it and possibly a 14x1 or 7x2 0.1" connector
pad on it, either direct soldered to the larger board, or perhaps with
a connector. A bare VFD would just have its leads coming out of the
glass, right to the only PCB you are looking at.
If the microcontroller is an MCS51-family part (8051 and on up to
quite modern devices), it should be easy to trace out large portions
of its circuit with little effort. At 100% schematic usually takes a
long time, but there is often much you can do with some of the core
If there are obvious serial interface chips (1488/1489, or MAX232, or
perhaps a 9636/9637-type 8-pin DIP), it might be easy to see a) how to
talk and listen, and b) if you need voltages other than just +5VDC.
VFDs require something odd - perhaps 36V?, and the formatted VFDs I've
seen (and unformatted VFDs on HP printer frontpanels) have a switching
supply right there so they _do_ only need +5V. Something from a
telephone device might be able to reduce +48V down to what it needs
locally, since that's a common voltage in switch gear.
Tracing buttons to the microcontroller should be easy. If you are
lucky, pressing one would cause the MCU to send out events
spontaneously. If you are unlucky, you'd need to send the unit some
sort of init code or keypad unlock code first.
If you take a few photos (especially if they are properly focused),
it's possible to divine much from a visual inspection.
If you cannot find docs and the VFD looks formatted, it might be worth
cutting out the MCU and wiring your own in its place. There are
projects around that use PICs and AVRs to talk to LCDs and VFDs that
are HD44780-controller-compatible, and many of those also have
provisions for buttons and lights.
At some point, if you do get it working, especially if you get it
working without hardware mods, I can recommend writing an LCDproc
driver for it (http://www.lcdproc.org/). That way, you can use
existing control software and existing clients to do interesting
things with your display without resorting to writing everything from
the ground up. I've written several LCDproc drivers for a variety of
serial-interfaced devices, and debugged drivers for several other
interface types. It's not too hard to do if you know C.
I'm interested to see pictures, especially since I already do so much
with displays and LCDproc.
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