EEVblog #717 - How To Hack Vacuum Fluorescent Displays

[EEVblog]

Dave explains what Vacuum Fluorescent Displays (VFD's) are, how they work, and then hacks an interface and reverse engineers a surplus display from an industrial machine to make it work with an Arduino.

TI TL4810 VFD Driver chip: http://html.alldatasheet.com/html-pdf/156237/TI/TL4810B/84/3/TL4810B.html

[mikeselectricstuff]

Some nice info from Noritake Itron on VFD principles :
http://www.noritake-elec.com/vfd_operation.html

[dentaku]

That was quite interesting and educational.
It was more of a Mike's Electric Stuff style project/hack but closer to something a beginner could do.

[bktemp]

Great explanation of how VFDs work, without going to much into details!
There is also a reverse construction type with the anodes at the front glass and the grids and filament mounted behind.

Some notes for people who want do drive bare VFDs:
The anode/grid voltage depends on the multiplex ratio (the number of grids). For static drive displays (single grid) it can be as low as 10V or up to 70V for large displays with >50 grids.
Up to around 10 grids it is possible to use 4000 series logic (4094 as anode and grid driver) at up to 18V with decent brightness.
There is also an easy way for estimating the filament voltage:
Because the filament needs a certain temperature to emit electrons, all you need to do is measure its temperature and adjust the voltage. Since tungsten has a positive temperature coefficient it can be used as a temperature sensor: The hot resistance is typically in the range of 4x the cold resistance. This should give a dim glowing filament wire.

It is a good idea to start at a lower anode voltage and add some watchdog timer or other fail safe mechanism that shuts down the anode supply if the grid multiplexing fails. Otherwise the phosphor at the anodes burns away really fast at high voltages.

[Ketturi]

I love VFD's. Still best looking display technology excluding OLEDs. Dave got easy one to reverse engineer, those are kinda off the shelf modules that are best for own projects.

I have project of my own with much more complicated driver board, but I just hacksawed a part out where display and buffers & shift register were, and coded my own multiplexed display driver. Easier than reverse engineering old 8085 machine code from cpu that drives 3x 6 digit 7-segment and one 32 digit 14 segment alphanumeric VFD-displaydisplays. And seems to be not standard ASCII. They do not have their own power supply, so I have problem of finding 5VAC + 40V DC VFD psu module.

[firewalker]

Any chance for it to be "Hitachi" compatible?

Alexander.

[helius]

Nice video! I like these displays, too.
A note on the need to use special high-voltage driver circuits: there are some special VFDs referred to as "Chip-In-Glass" or CIG that have integrated drivers and a shift register. So when interfacing these you only need to supply the B+ anode voltage, and clock bits in at regular TTL levels.
http://www.noritake-itron.com/NewWeb/GVFD/AppNotes/CIG.asp

Any chance for it to be "Hitachi" compatible?

There are graphic VFD modules compatible with HD61202: http://www.noritake-elec.com/guu100.php
They are advertised as drop-in replacements, but the glass panel may not be exactly the same size.

[nitro2k01]

I don't know what you tried of course, but an unknown pin may be an address ("A0") pin for sending special commands. Another good bet is that it may be using ANSI escape sequences. Byte 27 (often written as oct 33 or hex 1B) followed by a command sequence.

Would have been fun to see a mini reverse engineering of the drive circuit.

[rollatorwieltje]

If you need a VFD, try to get a "customer display" for a cash register. These things seem to always use RS232 and listen to the standard ASCII commands + escape codes to define custom fonts etc. A typical controller for these things is a Samsung 20L203DA5.

[deephaven]

Interesting video.

Bad form that Dave didn't acknowledge who sent it in (it wasn't me!). Whoever it was went to the trouble and expense of sending it in so at least Dave should have mentioned who it was. Being too busy isn't an excuse, it would take no time to stash these items on a shelf with the original sender's name on them.

[dentaku]

Interesting video.

Bad form that Dave didn't acknowledge who sent it in (it wasn't me!). Whoever it was went to the trouble and expense of sending it in so at least Dave should have mentioned who it was. Being too busy isn't an excuse, it would take no time to stash these items on a shelf with the original sender's name on them.

It was from Mark Butterworth of Santa Clara California.

[Hydrawerk]

See also https://www.eevblog.com/forum/microcontrollers/itron-noritake-gu256x64-312-avr-library-needed/
http://kimboricha.blogspot.kr/2013/10/noritake-itron-gu256x64-901a-vfdvacuum.html

[Dinsdale]

Hay, what about "clear screen"?
What about "cursor position"?
Only 35 min.? You got a half hour to go!
And 25fps? I can't see anything!
 
But, really, I enjoyed it.

[deephaven]

Interesting video.

Bad form that Dave didn't acknowledge who sent it in (it wasn't me!). Whoever it was went to the trouble and expense of sending it in so at least Dave should have mentioned who it was. Being too busy isn't an excuse, it would take no time to stash these items on a shelf with the original sender's name on them.

It was from Mark Butterworth of Santa Clara California.

Well, spotted, thanks dentaku and thank you Mark if you're watching 

[gslick]

Maybe the NEC microcontroller is an MCS-48 architecture uPD80C48 / uPD80C49?

http://www.cpu-world.com/info/Pinouts/8048.html

Do the data line inputs match the DB0-DB7 I/O pins 12-19?
Is the 12MHz crystal connected to XTAL1 and XTAL2 pins 2 and 3?

[nitro2k01]

Maybe the NEC microcontroller is an MCS-48 architecture uPD80C48 / uPD80C49?

http://www.cpu-world.com/info/Pinouts/8048.html

Do the data line inputs match the DB0-DB7 I/O pins 12-19?
Is the 12MHz crystal connected to XTAL1 and XTAL2 pins 2 and 3?

Yes and yes.

[TheEPROM9]

I have designed my own discreet logic driver for a VFD, the clock part has never been built but the display is now fully driven.

Here's a link to my website on the subject: http://www.eprom9.comeze.com/VFD%20clock.html





If you want more info on the project just message me. Voltage is 5V for the filaments and 12V for everything else.

[EEVblog]

Bad form that Dave didn't acknowledge who sent it in (it wasn't me!). Whoever it was went to the trouble and expense of sending it in so at least Dave should have mentioned who it was. Being too busy isn't an excuse, it would take no time to stash these items on a shelf with the original sender's name on them.

I normally do that, but in this case must have forgotten the letter.

[deephaven]

Bad form that Dave didn't acknowledge who sent it in (it wasn't me!). Whoever it was went to the trouble and expense of sending it in so at least Dave should have mentioned who it was. Being too busy isn't an excuse, it would take no time to stash these items on a shelf with the original sender's name on them.

I normally do that, but in this case must have forgotten the letter.

Thanks for responding, Dave, and for not flaming me. I still gave the video a 

[dentaku]

Bad form that Dave didn't acknowledge who sent it in (it wasn't me!). Whoever it was went to the trouble and expense of sending it in so at least Dave should have mentioned who it was. Being too busy isn't an excuse, it would take no time to stash these items on a shelf with the original sender's name on them.

I normally do that, but in this case must have forgotten the letter.

I don't think it's terribly important but if you wanted to, could you use the Youtube annotation tool to add "Mark Butterworth of Santa Clara California" at the point in the video where you say you can't remember where you got the VFD from?

[twice11]

Maybe the NEC microcontroller is an MCS-48 architecture uPD80C48 / uPD80C49?

http://www.cpu-world.com/info/Pinouts/8048.html

Do the data line inputs match the DB0-DB7 I/O pins 12-19?
Is the 12MHz crystal connected to XTAL1 and XTAL2 pins 2 and 3?

Yes and yes.

Good find, but likely, it's not the master processor, the 8048, but the slave processor, the 8041/8042. The pinout is quite similar - and we get the following connector pinout:

• Arduino 2 = /CS (Pull low to activate the interface)
• Arduino 3 = /RD (Pull low to read data from the 8042)
• Arduino 4 = Address (often 0 = 'data', 1 = 'command')
• Arduino 5 = /WR (Pull low to write data to the 8032)

So what Dave is doing while he writes the letters of "H" is toggling between the invalid pattern where /RD and /WR are both low (active) and the pattern where only /WR is active. This explains why in the end the rising edge of PIN 3 activates the read, while a write is typically initiated by activating (pulling low) the write pin: Deactivating (pulling high) pin 3 results in a valid write instruction.

[EEVblog]

Found the datasheet:
http://www.eevblog.com/files/Babcock-VF0240.pdf

[gslick]

Good find, but likely, it's not the master processor, the 8048, but the slave processor, the 8041/8042. The pinout is quite similar - and we get the following connector pinout:

• Arduino 2 = /CS (Pull low to activate the interface)
• Arduino 3 = /RD (Pull low to read data from the 8042)
• Arduino 4 = Address (often 0 = 'data', 1 = 'command')
• Arduino 5 = /WR (Pull low to write data to the 8032)

Yes, that makes more sense. Taking another look at the still image of the PCB card edge connector it looks like the control signals from the card edge connector go to pins 6, 8, 9, 10 of the 40-pin microcontroller.

With the standard 8049 pinouts that would be:
Pin 6: /INT (input)
Pin 8: /RD (output)
Pin 9: /PSEN (output)
Pin 10: /WR (output).
The direction of those signals wouldn't make sense for the usage scenario here.

With the standard 8042 pinouts that would be:
Pin 6: /CS (input)
Pin 8: /RD (input)
Pin 9: A0 (input)
Pin 10: /WR (input).
The direction of those signals does make sense here.

[AlphZeta]

I did a VFD clock project a while ago, and explained from how to properly drive a VFD filament to building the driver circuit.  You can find the series below:

Filament driver:
http://www.kerrywong.com/2013/06/05/vfd-filament-driver-using-555/

VFD driver:
http://www.kerrywong.com/2013/06/13/a-diy-vacuum-fluorescent-display-driver/

And the VFD Clock:
http://www.kerrywong.com/2013/07/01/vfd-clock-putting-everything-together/

[bktemp]

I did a VFD clock project a while ago, and explained from how to properly drive a VFD filament to building the driver circuit.  You can find the series below:

Filament driver:
http://www.kerrywong.com/2013/06/05/vfd-filament-driver-using-555/

VFD driver:
http://www.kerrywong.com/2013/06/13/a-diy-vacuum-fluorescent-display-driver/

And the VFD Clock:
http://www.kerrywong.com/2013/07/01/vfd-clock-putting-everything-together/

Looks a bit too complicated. All those level shifters around the ULN2003 can be easily avoided: Since you already have a floating filament supply, connect the center tap to a negative voltage instead of +5V. Now you can use simple PNP transistors directly driven by 5V oder 3.3V logic to drive the grids and anodes to the required voltage levels. To prevent ghosting you can add pulldown resistors from each anode/grid to the cathode potential. This is how it is done in many cheap VFD drivers using a single chip microcontroller/VFD driver.