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2x20 VFD

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Ben Solon

Thu Apr 25 2013, 12:34AM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

I got this awesome 2x20 dot character display from a functional cash register type commercial display, but I can't seem to be able to pull up any datasheet. The closest I could find was the unit's manual here

, and that the manufacturer is here

itron has (what i believe to be) my display, but it's the only one with no datasheet, and it's too different from the rest anyways.

The display uses 14 total pins and is able to write to every character. Can anyone point me towards some information on how I can begin determining pins without any method of driving it?

Conundrum

Thu Apr 25 2013, 09:21PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

I used to have one here, IIRC it has the voltage converter onboard.
Normally there is a large capacitor, which tells you the main Vcc and Gnd configuration.

Ben Solon

Thu Apr 25 2013, 11:18PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

what type of voltage converter? one that steps vcc up to plate voltage?

It appears that 6 are used for vcc, gnd, and filament. they each are doubled up on the header. that leaves 8 unknown pins.

I doubt that its possible to drive all the characters in any sort of parallel or multiplexed configuration with just 8 pins, so there might be some sort of built in control. the internal dc-dc supports that there's additional circuitry built in.

Conundrum, do you remember what the voltage specs are for the display? the cap is rated 16v, the original control board contained a set of 34063 IC's that ran on 5v in. Maybe 12v typical?

Conundrum

Fri Apr 26 2013, 07:16PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

IIRC the heater was 3.6V not 6.3, you want it to be barely visible in a dark room.
These tubes normally need between 8 and 25V, see

Also see

I've used the 9Vs in series method before, you should add a 1K resistor to limit current though.

...

Fri Apr 26 2013, 09:35PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

possibly a hd44780 interface? Although I have never seen a VFD with that few pins coming out of the glass. Does the control board it is (was?) connected to have any hints?

Ben Solon

Sat Apr 27 2013, 02:01AM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

thanks conundrum, that helps a lot

wouldn't want to be frying anything when I go to power it on.

... wrote ...

possibly a hd44780 interface? Although I have never seen a VFD with that few pins coming out of the glass. Does the control board it is (was?) connected to have any hints?

That's what i've been concerned about. I have yet to go through the datasheets of the ic's on the control board, but it has 2 old rare uC's plus an avr at89 series uC by the serial input, so I think it;s going to have to be some funny interface.

edit: the uC's mounted are the w78c032c40dl and the w27c512-45. The input is managed by the uart module inside of a AT89C2051-24pu. The w78c032c40dl is a 7v max device running on a 5v supply. 6 of it's pins are connected to go straight into the vfd. So now we have:
1(pwr?)
2(pwr?)
3(5v IO)
4(5v IO)
5(5v IO)
6(5v IO)
7(5v IO)
8(5v IO)
9(filliment end 1)
10(filliment end 1)
11(boost regulated voltage)
12(boost regulated voltage)
13(filliment end 2)
14(filliment end 2)

edit2: this supports your theory about some sort of 44780 interface- RS, R/W, Data1-4(or Data4-5).

Wolfram

Sat Apr 27 2013, 12:04PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

I'm pretty sure it's not a 44780-compatible interface. Cash register displays are usually quite primitive, with shift registers and drivers on the board with the display, but no memory or scanning logic, so they have to be continously updated from the driving eletronics. The low number of pins from the actual glass display probably means that the VFD has internal driver chips inside the glass package. If you want to drive it, I think the simplest approach is to use the original driver board and figure out how to communicate with it serially, or use a logic analyzer to see what kind of signals the driver board sends to the VFD board.

macona

Thu May 02 2013, 07:57AM

Registered Member #3272 Joined: Mon Oct 04 2010, 11:40PM
Location: Beaverton, OR
Posts: 101

Definitely not 44870 compatible. The register VFDs usually use a serial interface to send data to the display. Running a parallel interface to something like this would be silly if all you really needed is three wires, +5v, gnd, and data. Apparently a lot of cash registers use a protocol called AEDEX like this

Ben Solon

Thu May 02 2013, 02:35PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

Well unfortunately I managed to drop the display off of my lap the other day

So I ordered a couple Futaba VFDs with a much more standard- yet still painfull interface. It's a 5x7 16 character with underscores. so I have 36 anodes and 16 grids to drive. Much easier to implement now that I have a datasheet to work with, but there are still 52 pins to drive at >TTL levels. Is a discrete driver too absurd with this many pins, or are there IC's that are meant for the dot matrix multiplexed type of driving that this vfd requires? Otherwise I'm off to design 52 level shifting discrete buffers within a reasonably small PCB size...

macona

Sun May 05 2013, 07:52PM

Registered Member #3272 Joined: Mon Oct 04 2010, 11:40PM
Location: Beaverton, OR
Posts: 101

A friend of mine sells these Noritake displays:

They work great. I have used them in several projects connected to an teensy or arduino. They are 44870 compatible.

Says they are out but I know they have more. Just call them.

One of the ones I used:

IMGP6084 by macona, on Flickr

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